• IR detector system, biasing of photo diode

    From Klaus Vestergaard Kragelund@21:1/5 to All on Sun Oct 27 02:19:14 2024
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 02:05:26 2024
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy,
    not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise, specifically the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as baffles, tubes, and so on.

    Check out the Hamamatsu S6968–super good medicine.

    Cheers

    Phil Hobbs




    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Sat Oct 26 19:26:32 2024
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.

    Just don't fry the photodiode in high light.

    An optical bandpass filter would hugely improve things, take out most
    of the sunlight.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to Phil Hobbs on Sun Oct 27 14:50:54 2024
    On 27/10/2024 1:05 pm, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the buried signal in the DC from sunlight.

    If the sunlight signal doesn't just saturate the signal chain, which
    wrecks the gain.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    Bias doesn't really matter unless you are looking for avalanche
    multiplication of the charge carriers - if there there's enough bias to
    let you collect all of them. Single photon avalanche diodes are a
    different can of worms, but you should have plenty of photons, so why
    would you bother?

    More bias does reduce the capacitance across the detection diode, making
    it a bit faster, but the reduction is a hyperbolic function of bias, so
    each extra volt makes progressively less difference.

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy, not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise, specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as baffles, tubes, and so on.

    In a vaguely similar sort of situation I got my mechanical colleagues to
    put a graphite liner inside the tube, and cut a screw thread into the
    liner. They thought I was nuts, until they skipped cutting the screw
    thread and I promptly complained about the loss of performance.

    Check out the Hamamatsu S6968–super good medicine.

    Hamamatsu do seem to have good products.

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to john larkin on Sun Oct 27 08:41:51 2024
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.

    Just don't fry the photodiode in high light.

    An optical bandpass filter would hugely improve things, take out most
    of the sunlight.





    Yes, the classic solution was to operate PD into an inductor so DC didn’t overload.


    --
    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to Kragelund on Sun Oct 27 09:03:20 2024
    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>:

    Hi

    I am working on an IR detector that will guide a robot into a docking >station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat. Cheap electret mikes? or modify some ebay 1 dolalr distance sensors...
    can be used for anti-collision too.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Phil Hobbs on Sun Oct 27 13:20:32 2024
    On 27-10-2024 03:05, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy, not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise, specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as baffles, tubes, and so on.


    I have tried to search for optical filters. Where would one get those?

    Baffles and tubes, we can do ourselves, any guideline on the best
    surface of the inner tube?

    Check out the Hamamatsu S6968–super good medicine.


    Looks like a very big die. Is that the main reason to use that one, to
    get better sensitivity?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Jan Panteltje on Sun Oct 27 13:29:19 2024
    On 27-10-2024 10:03, Jan Panteltje wrote:
    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard
    Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat. Cheap electret mikes? or modify some ebay 1 dolalr distance sensors...
    can be used for anti-collision too.


    I have looked into both ultrasonics and also magnetic coil pickup. I
    suggested ultrasound since we could do object detection as you mention,
    but the client really likes the IR concept, so need to follow that path
    for now.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to john larkin on Sun Oct 27 13:26:40 2024
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Bill Sloman on Sun Oct 27 13:21:48 2024
    On 27-10-2024 04:50, Bill Sloman wrote:
    On 27/10/2024 1:05 pm, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the buried signal in the DC from sunlight.

    If the sunlight signal doesn't just saturate the signal chain, which
    wrecks the gain.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    Bias doesn't really matter unless you are looking for avalanche multiplication of the charge carriers - if there there's enough bias to
    let you collect all of them. Single photon avalanche diodes are a
    different can of worms, but you should have plenty of photons, so why
    would you bother?

    More bias does reduce the capacitance across the detection diode, making
    it a bit faster, but the reduction is a hyperbolic function of bias, so
    each extra volt makes progressively less difference.


    Ok, noted :-)
    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy, >> not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise,
    specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as
    baffles,
    tubes, and so on.

    In a vaguely similar sort of situation I got my mechanical colleagues to
    put a graphite liner inside the tube, and cut a screw thread into the
    liner. They thought I was nuts, until they skipped cutting the screw
    thread and I promptly complained about the loss of performance.

    Check out the Hamamatsu S6968–super good medicine.

    Hamamatsu do seem to have good products.


    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 13:40:18 2024
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 13:42:27 2024
    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:

    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 23:53:36 2024
    On 27/10/2024 11:20 pm, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:05, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy, >> not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise,
    specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as
    baffles,
    tubes, and so on.


    I have tried to search for optical filters. Where would one get those?

    You could try Edmund Optics

    https://www.edmundoptics.com/

    I've got their 2023 catalogue on my bookshelf, and they offer a bunch of
    narrow band interference filter, at least some designed to pick out
    specific diode laser lines. They aren't cheap.

    <snip>

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 06:05:02 2024
    On 10/26/2024 5:19 PM, Klaus Vestergaard Kragelund wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking station.

    A IR transmitter on the docking station transmits a beam, and 2 IR detectors on
    the robot detects the beam and lets the robot navigate towards the target. The
    working distance is a couple of meters.

    Can the robot ALWAYS see the docking station? What happens if an
    obstacle (wall?) comes between the two?

    Can either device (robot/dock) ever slip out of the shared plane?

    Can the docking station be moved, from day to day, site to site, etc.?

    Is the arena indoors?

    I have become particularly fond of using cameras to interface with
    the real world. Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to piglet on Sun Oct 27 14:06:43 2024
    piglet <erichpwagner@hotmail.com> wrote:

    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datashee
    t/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absor
    ption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.

    Just don't fry the photodiode in high light.

    An optical bandpass filter would hugely improve things, take out most
    of the sunlight.





    Yes, the classic solution was to operate PD into an inductor so DC didn’t overload.

    Go one step further and make the indusctor part of a parallel resonant
    circuit tuned to the modulation frequency.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Don Y on Sun Oct 27 15:33:53 2024
    On 27-10-2024 14:05, Don Y wrote:
    On 10/26/2024 5:19 PM, Klaus Vestergaard Kragelund wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    Can the robot ALWAYS see the docking station?  What happens if an
    obstacle (wall?) comes between the two?


    Yes, we have RTK GPS to position it within a cm at a location right in
    front of the docking, 2 meters away.

    Can either device (robot/dock) ever slip out of the shared plane?

    No, should be locked


    Can the docking station be moved, from day to day, site to site, etc.?

    That is fixed


    Is the arena indoors?

    Outdoors

    I have become particularly fond of using cameras to interface with
    the real world.  Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...


    That's also a solution we have been working on. The Worx Vision uses that

    https://eu.worx.com/da-dk/landroid/vision-technology/

    That is for a future version. Cameras can also be blinded, lenses needs
    to be cleaned etc

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Liz Tuddenham on Sun Oct 27 15:35:45 2024
    On 27-10-2024 15:06, Liz Tuddenham wrote:
    piglet <erichpwagner@hotmail.com> wrote:

    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datashee >>>> t/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absor >>>> ption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.

    Just don't fry the photodiode in high light.

    An optical bandpass filter would hugely improve things, take out most
    of the sunlight.





    Yes, the classic solution was to operate PD into an inductor so DC didn’t
    overload.

    Go one step further and make the indusctor part of a parallel resonant circuit tuned to the modulation frequency.

    Yes, like Larkin wrote. Like this:

    https://www.electro-tech-online.com/threads/lc-tuned-circuit-using-parasitic-cs-photodiode-preamp.99230/

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Sun Oct 27 10:49:27 2024
    On Sun, 27 Oct 2024 13:42:27 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    A photodiode won't saturate as long as it has a few volts of DC across
    it. It might melt if there's no current limiting.


    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:

    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    The LC tank combines background light rejection and bandpass filtering
    and has high signal gain, with two parts.

    I think there are photodiodes with colored plastic, essentially a
    cheap optical bandpass filter. Used in TV remote receivers.

    The windows in TVs may be optical bandpass filters too. They work with
    very little signal from the remote, in high room light.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Sun Oct 27 11:08:10 2024
    On Sun, 27 Oct 2024 13:20:32 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 03:05, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy,
    not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise, specifically >> the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as baffles, >> tubes, and so on.


    I have tried to search for optical filters. Where would one get those?

    Google has lots of hits. One square foot of plastic-film BP stuff
    could be choped up into maybe 10,000 little filters.

    Ask for samples!


    Baffles and tubes, we can do ourselves, any guideline on the best
    surface of the inner tube?

    Check out the Hamamatsu S6968–super good medicine.


    Looks like a very big die. Is that the main reason to use that one, to
    get better sensitivity?

    At 10 KHz, gain is cheap.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to All on Sun Oct 27 10:56:42 2024
    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard >Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat. >Cheap electret mikes? or modify some ebay 1 dolalr distance sensors...
    can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could
    be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Cheap electret mikes have gain inside, a jfet or an IC, so there would
    be lots of signal to go straight into a uP ADC pin.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 12:06:30 2024
    On 10/27/2024 7:33 AM, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 14:05, Don Y wrote:
    On 10/26/2024 5:19 PM, Klaus Vestergaard Kragelund wrote:
    I am working on an IR detector that will guide a robot into a docking station.

    A IR transmitter on the docking station transmits a beam, and 2 IR detectors
    on the robot detects the beam and lets the robot navigate towards the
    target. The working distance is a couple of meters.

    Can the robot ALWAYS see the docking station?  What happens if an
    obstacle (wall?) comes between the two?

    Yes, we have RTK GPS to position it within a cm at a location right in front of
    the docking, 2 meters away.

    Then why can't you move to the GPS location of the dock with the
    same degree of accuracy?

    Can either device (robot/dock) ever slip out of the shared plane?

    No, should be locked

    "Outdoors" (from below). Presumably on pavement/concrete (not a "lawn")
    that wouldn't have dips and bumps?

    Can the docking station be moved, from day to day, site to site, etc.?

    That is fixed

    Is the arena indoors?

    Outdoors

    I have become particularly fond of using cameras to interface with
    the real world.  Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...

    That's also a solution we have been working on. The Worx Vision uses that

    https://eu.worx.com/da-dk/landroid/vision-technology/

    That is for a future version. Cameras can also be blinded, lenses needs to be cleaned etc

    Yes, but a camera can be "queried" to verify that it is functioning
    correctly: "What do you see? Is it THIS?"

    I test my cameras by storing previously viewed scenes to verify they
    are still "reasonably" intact. Ideally, I would move something into
    the field of view but that requires additional capabilities.

    You, however, could move the robot (assuming IT has the eyes) and
    verify that the scene changes accordingly.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to john larkin on Sun Oct 27 16:39:24 2024
    On Sun, 27 Oct 2024 10:49:27 -0700, john larkin <JL@gct.com> wrote:

    On Sun, 27 Oct 2024 13:42:27 +0100, Klaus Vestergaard Kragelund ><klauskvik@hotmail.com> wrote:

    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>> lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    A photodiode won't saturate as long as it has a few volts of DC across
    it. It might melt if there's no current limiting.


    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:
    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    The LC tank combines background light rejection and bandpass filtering
    and has high signal gain, with two parts.

    I think there are photodiodes with colored plastic, essentially a
    cheap optical bandpass filter. Used in TV remote receivers.

    The windows in TVs may be optical bandpass filters too. They work with
    very little signal from the remote, in high room light.

    To this I would add a trick. We know something very useful about the
    10 KHz modulation, its exact frequency, given that it is (or can be)
    generated electronically, and thus its frequency is ultimately
    controlled by a logic-clock crystal oscillator.

    So feed the amplified signal from the 10 KHz LC tank to a I+Q homodyne
    circuit, filter to pass signals from DC to a 10 Hz and compute the
    magnitude of the received signal - this is used for figuring out the
    direction to the docking station.

    The phase of the received signal is discarded, as it is effectively
    random because the TX oscillator phase with respect to the RX
    oscillator phases is uncontrolled and unknown.

    The advantage over a high-Q LC tank is that the resonant frequency of
    the tank need not be that precise.


    Joe Gwinn

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to john larkin on Sun Oct 27 21:16:11 2024
    john larkin <JL@gct.com> wrote:

    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus >Vestergaard Kragelund <klauskvik@hotmail.com> wrote in ><vfk0u0$3u9en$1@dont-email.me>:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>detectors on the robot detects the beam and lets the robot navigate >>towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, >and just a simple Microchip PIC : for processing It can, with some added >code, track object forms too, like a cross or maybe a big character. >panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi those camara >modulea are IR sensitive to some extend, sometimes you can remove the IR >filter from such modules. It may be a bit of overkill for your
    application, but OTOH it can do a lot more. Mainly designed to detect and >follow jet exhaust.. You could uee utrasonics too, maybe even simpler, no >sun problem, like a bat. Cheap electret mikes? or modify some ebay 1
    dolalr distance sensors... can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could
    be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Terrible problems with acoustic reflections.


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to Klaus Vestergaard Kragelund on Sun Oct 27 22:59:59 2024
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single transistor or op amp could take the role of inductor.

    --
    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to erichpwagner@hotmail.com on Sun Oct 27 19:34:25 2024
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single >transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to Liz Tuddenham on Mon Oct 28 07:03:34 2024
    On a sunny day (Sun, 27 Oct 2024 21:16:11 +0000) it happened liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote in <1r23uzl.g0c7e315xtehyN%liz@poppyrecords.invalid.invalid>:

    john larkin <JL@gct.com> wrote:

    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus
    Vestergaard Kragelund <klauskvik@hotmail.com> wrote in
    <vfk0u0$3u9en$1@dont-email.me>:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, >> >and just a simple Microchip PIC : for processing It can, with some added
    code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi those camara
    modulea are IR sensitive to some extend, sometimes you can remove the IR
    filter from such modules. It may be a bit of overkill for your
    application, but OTOH it can do a lot more. Mainly designed to detect and >> >follow jet exhaust.. You could uee utrasonics too, maybe even simpler, no >> >sun problem, like a bat. Cheap electret mikes? or modify some ebay 1
    dolalr distance sensors... can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could
    be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Terrible problems with acoustic reflections.

    Could be a problem, depends on the situation
    I once build a 44 kHz Doppler radar that would even detect if I blinked an eye..
    https://panteltje.nl/pub/experiment_with_44kHz_doppler_from_philips_remote_control_IXIMG_0758.JPG
    I also have so RF Doppler motion sensors in use... Tsting:
    https://panteltje.nl/pub/wrapped_RF_doppler_motion_sensor_IXIMG_0797.JPG
    those are REALLY sensitive.
    Thats is the type of sensor that opens the doors in the shop for you if you want to enter / leave.
    Also just a few dollar on ebay, and very small.

    And you can combine sensors...

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to john larkin on Mon Oct 28 20:46:05 2024
    On 28/10/2024 4:49 am, john larkin wrote:
    On Sun, 27 Oct 2024 13:42:27 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>> lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    A photodiode won't saturate as long as it has a few volts of DC across
    it. It might melt if there's no current limiting.


    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:

    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    The LC tank combines background light rejection and bandpass filtering
    and has high signal gain, with two parts.

    It also shifts the phase of the output voltage quite rapidly as the
    modulation frequency moves across the resonant frequency, or as the temperature dependent resonant frequency drifts across the modulation frequency.

    I think there are photodiodes with colored plastic, essentially a
    cheap optical bandpass filter. Used in TV remote receivers.

    The windows in TVs may be optical bandpass filters too. They work with
    very little signal from the remote, in high room light.

    If you want serious filtering, look for multilayer interference filters.
    they aren't cheap but they can be quite narrowband.

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Joe Gwinn on Mon Oct 28 11:08:50 2024
    On 27-10-2024 21:39, Joe Gwinn wrote:
    On Sun, 27 Oct 2024 10:49:27 -0700, john larkin <JL@gct.com> wrote:

    On Sun, 27 Oct 2024 13:42:27 +0100, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>> current, frequency modulated so that the receiver can ignore the effect >>>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>> lower, but does reduced the effective range of the system during >>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>> photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>> the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light. >>
    A photodiode won't saturate as long as it has a few volts of DC across
    it. It might melt if there's no current limiting.


    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:

    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    The LC tank combines background light rejection and bandpass filtering
    and has high signal gain, with two parts.

    I think there are photodiodes with colored plastic, essentially a
    cheap optical bandpass filter. Used in TV remote receivers.

    The windows in TVs may be optical bandpass filters too. They work with
    very little signal from the remote, in high room light.

    To this I would add a trick. We know something very useful about the
    10 KHz modulation, its exact frequency, given that it is (or can be) generated electronically, and thus its frequency is ultimately
    controlled by a logic-clock crystal oscillator.

    So feed the amplified signal from the 10 KHz LC tank to a I+Q homodyne circuit, filter to pass signals from DC to a 10 Hz and compute the
    magnitude of the received signal - this is used for figuring out the direction to the docking station.

    Very nice, sort of like for lock-in detection, I have done that before,
    works great. Would take the tolerances out of the passive components.


    The phase of the received signal is discarded, as it is effectively
    random because the TX oscillator phase with respect to the RX
    oscillator phases is uncontrolled and unknown.

    The advantage over a high-Q LC tank is that the resonant frequency of
    the tank need not be that precise.


    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to john larkin on Mon Oct 28 11:11:38 2024
    On 27-10-2024 18:56, john larkin wrote:
    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard
    Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>: >>
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat.
    Cheap electret mikes? or modify some ebay 1 dolalr distance sensors...
    can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could
    be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Could also be done with a chirp and auto-correlation, although this does
    not use the phase, but a beacon reference instead

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Don Y on Mon Oct 28 11:17:56 2024
    On 27-10-2024 20:06, Don Y wrote:
    On 10/27/2024 7:33 AM, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 14:05, Don Y wrote:
    On 10/26/2024 5:19 PM, Klaus Vestergaard Kragelund wrote:
    I am working on an IR detector that will guide a robot into a
    docking station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    Can the robot ALWAYS see the docking station?  What happens if an
    obstacle (wall?) comes between the two?

    Yes, we have RTK GPS to position it within a cm at a location right in
    front of the docking, 2 meters away.

    Then why can't you move to the GPS location of the dock with the
    same degree of accuracy?


    The docking station is typically in a shed, or close to a building where
    the GPS signal disappears.

    Can either device (robot/dock) ever slip out of the shared plane?

    No, should be locked

    "Outdoors" (from below).  Presumably on pavement/concrete (not a "lawn") that wouldn't have dips and bumps?


    It's moving on grass, and can have bumps etc, so for IR the lope needs
    to be perhaps 20degrees to avoid loss of signal

    Can the docking station be moved, from day to day, site to site, etc.?

    That is fixed

    Is the arena indoors?

    Outdoors

    I have become particularly fond of using cameras to interface with
    the real world.  Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...

    That's also a solution we have been working on. The Worx Vision uses that

    https://eu.worx.com/da-dk/landroid/vision-technology/

    That is for a future version. Cameras can also be blinded, lenses
    needs to be cleaned etc

    Yes, but a camera can be "queried" to verify that it is functioning correctly:  "What do you see?  Is it THIS?"

    I test my cameras by storing previously viewed scenes to verify they
    are still "reasonably" intact.  Ideally, I would move something into
    the field of view but that requires additional capabilities.

    You, however, could move the robot (assuming IT has the eyes) and
    verify that the scene changes accordingly.


    Could be done. The guys in charge are worried with change of
    environment, so what happens when it snows heavily, fog or other
    surroundings changing effects.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 05:01:16 2024
    On 10/28/2024 3:17 AM, Klaus Vestergaard Kragelund wrote:
    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    Can the robot ALWAYS see the docking station?  What happens if an
    obstacle (wall?) comes between the two?

    Yes, we have RTK GPS to position it within a cm at a location right in front
    of the docking, 2 meters away.

    Then why can't you move to the GPS location of the dock with the
    same degree of accuracy?

    The docking station is typically in a shed, or close to a building where the GPS signal disappears.

    Ah, OK.

    Can either device (robot/dock) ever slip out of the shared plane?

    No, should be locked

    "Outdoors" (from below).  Presumably on pavement/concrete (not a "lawn")
    that wouldn't have dips and bumps?

    It's moving on grass, and can have bumps etc, so for IR the lope needs to be perhaps 20degrees to avoid loss of signal

    And, presumably, they are short (time and space) transients? *Faster*
    than the response time of the robots controls?

    I have become particularly fond of using cameras to interface with
    the real world.  Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...

    That's also a solution we have been working on. The Worx Vision uses that >>>
    https://eu.worx.com/da-dk/landroid/vision-technology/

    That is for a future version. Cameras can also be blinded, lenses needs to >>> be cleaned etc

    Yes, but a camera can be "queried" to verify that it is functioning
    correctly:  "What do you see?  Is it THIS?"

    I test my cameras by storing previously viewed scenes to verify they
    are still "reasonably" intact.  Ideally, I would move something into
    the field of view but that requires additional capabilities.

    You, however, could move the robot (assuming IT has the eyes) and
    verify that the scene changes accordingly.

    Could be done. The guys in charge are worried with change of environment, so what happens when it snows heavily, fog or other surroundings changing effects.

    You extract salient "features" from the scene and use them.
    The robot doesn't need to be concerned about whether the ground is
    green, brown or white. Or, if the shed is in shade, blanketed
    with snow, etc.

    E.g., I use them to "watch" the garage door rails (which have a specific
    shape) to see if any objects have come between the camera and the rails.
    (The rails define the plane that the garage door will occupy as
    it closes) Of course, everything around the rails is highly variable
    as garages are notorious for clutter and dynamism.

    Another camera "watches" the mailbox by the road. In addition to
    the surroundings changing, there can be pedestrian and vehicular
    traffic passing at any time. In our case, it is illegal to
    drive while using a phone so folks often pull over to answer
    phone calls -- our mailbox is in a shaded area that seems to be
    highly desirable to such motorists-in-need. But, *their*
    vehicles don't look like "mail trucks" so no chance of thinking that
    *they* are delivering our mail...

    As I said before, it is a really great "sensor"! The downside is
    that you need resources to use it (your optical approach is likely
    possible with far less resources -- think of how robot vaccuum cleaners
    operate wrt their charging docks)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to Kragelund on Mon Oct 28 11:22:10 2024
    On a sunny day (Mon, 28 Oct 2024 11:17:56 +0100) it happened Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote in <vfnocj$uluj$3@dont-email.me>:

    On 27-10-2024 20:06, Don Y wrote:
    On 10/27/2024 7:33 AM, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 14:05, Don Y wrote:
    On 10/26/2024 5:19 PM, Klaus Vestergaard Kragelund wrote:
    I am working on an IR detector that will guide a robot into a
    docking station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    Can the robot ALWAYS see the docking station?  What happens if an
    obstacle (wall?) comes between the two?

    Yes, we have RTK GPS to position it within a cm at a location right in
    front of the docking, 2 meters away.

    Then why can't you move to the GPS location of the dock with the
    same degree of accuracy?


    The docking station is typically in a shed, or close to a building where
    the GPS signal disappears.

    Can either device (robot/dock) ever slip out of the shared plane?

    No, should be locked

    "Outdoors" (from below).  Presumably on pavement/concrete (not a "lawn")
    that wouldn't have dips and bumps?


    It's moving on grass, and can have bumps etc, so for IR the lope needs
    to be perhaps 20degrees to avoid loss of signal

    Can the docking station be moved, from day to day, site to site, etc.?

    That is fixed

    Is the arena indoors?

    Outdoors

    I have become particularly fond of using cameras to interface with
    the real world.  Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...

    That's also a solution we have been working on. The Worx Vision uses that >>>
    https://eu.worx.com/da-dk/landroid/vision-technology/

    That is for a future version. Cameras can also be blinded, lenses
    needs to be cleaned etc

    Yes, but a camera can be "queried" to verify that it is functioning
    correctly:  "What do you see?  Is it THIS?"

    I test my cameras by storing previously viewed scenes to verify they
    are still "reasonably" intact.  Ideally, I would move something into
    the field of view but that requires additional capabilities.

    You, however, could move the robot (assuming IT has the eyes) and
    verify that the scene changes accordingly.


    Could be done. The guys in charge are worried with change of
    environment, so what happens when it snows heavily, fog or other
    surroundings changing effects.

    You could put a RF transmitter in the thing,
    and measure for maximum signal with 2 separated receivers, like ham radio fox hunt,
    https://en.wikipedia.org/wiki/Transmitter_hunting
    then send the steering signal to the mobile thing via radio.
    Or use 2 transmitters and steerable antenna on the moving thing.,
    Bit of luck and yuo could use local radio stations...
    And at night use the stars.... :-) If it is not cloudy..
    My camera modules are Sony super HADs, ultra low light ones....
    https://www.ebay.com/itm/166096040231?
    analog video out, makes it very easy to process with with a Microchip PIC 18F14K22
    but I grew up with analog video.....

    There is lot more to it..
    These days with a simple Raspberry and a digital camara module in daylight object recognition is possible:
    https://core-electronics.com.au/guides/object-identify-raspberry-pi/
    Have not triad that.
    Seems fun :-)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From piglet@21:1/5 to john larkin on Mon Oct 28 12:14:52 2024
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>> lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still >>>> need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single
    transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver
    on the robot and two emitters on the docking station, a bit like aircraft
    VOR


    --
    piglet

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Don Y on Mon Oct 28 05:59:21 2024
    On 10/28/2024 5:01 AM, Don Y wrote:
    E.g., I use them to "watch" the garage door rails (which have a specific shape) to see if any objects have come between the camera and the rails.
    (The rails define the plane that the garage door will occupy as
    it closes)  Of course, everything around the rails is highly variable
    as garages are notorious for clutter and dynamism.

    "Track" would be a better term than "rail".

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Wanderer@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 11:24:36 2024
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)


    I believe you are looking for a daylight filter circuit.

    https://imgbox.com/MOri8WaP

    The photodiode converts light into current. The current either comes from the TIA
    feedback or the low pass feedback. The low pass feedback keeps the DC photodiode current
    out of the TIA feedback loop. So only the high frequency in the photodiode gets amplified
    a lot and trigger the comparator. TI used to make a part with all this built in. If
    you can find that datasheet, there is more detail in there.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to erichpwagner@hotmail.com on Mon Oct 28 08:21:56 2024
    On Mon, 28 Oct 2024 12:14:52 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>> current, frequency modulated so that the receiver can ignore the effect >>>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>> lower, but does reduced the effective range of the system during >>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>> photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>> the gain would be close to zero for the stage after. I would then still >>>>> need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single
    transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver
    on the robot and two emitters on the docking station, a bit like aircraft
    VOR

    A single combo microphone/loudspeaker on the robot would be
    interesting. Ranging is one obvious use.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Wanderer@21:1/5 to All on Mon Oct 28 11:39:57 2024
    It's Burr-Brown(I'm old) OPT201.

    https://electronix.org.ru/datasheet/Burr-Brown/AB-061%20-%20OPT201%20to%20reject%20ambient%20light.pdf

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Mon Oct 28 12:05:36 2024
    On Mon, 28 Oct 2024 11:11:38 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 18:56, john larkin wrote:
    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard
    Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>: >>>
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat.
    Cheap electret mikes? or modify some ebay 1 dolalr distance sensors...
    can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could
    be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Could also be done with a chirp and auto-correlation, although this does
    not use the phase, but a beacon reference instead

    Could that tell the direction of the mother ship?

    Three or four omni mems microphones could tell the robot which
    direction to go with full 360 degree coverage.

    Maybe even estimate range.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 15:16:50 2024
    On 2024-10-27 08:20, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:05, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too noisy, >> not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise,
    specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as
    baffles,
    tubes, and so on.


    I have tried to search for optical filters. Where would one get those?

    700-nm plastic longpass filter material comes in sheets. You can get
    smallish chunks of it on the jungle website and various other emporia.

    Fancier things, such as narrowish bandpasses and custom wavelengths,
    tend to be glass and quite a lot more expensive. I usually get those
    from Omega Optical, but there are European suppliers as well.

    For this use, a regular 700-nmm plastic longpass will get rid of most of
    the daylight, which is what you want. You can also get photodiodes with
    the filter material included, e.g. the ever-popular BPW34F.


    Baffles and tubes, we can do ourselves, any guideline on the best
    surface of the inner tube?

    Regular old flat black paint. But a lens on the transmitter will be the biggest win.


    Check out the Hamamatsu S6968–super good medicine.


    Looks like a very big die. Is that the main reason to use that one, to
    get better sensitivity?

    It has very low capacitance for its area, it has a lens to increase the detection area, and (crucially for my uses, which are generally at
    higher frequency) it has very very low series resistance.

    The series resistance of the diode contributes Johnson noise that can't
    be removed by bootstrapping. You don't care too much at 10 kHz, but at
    higher frequency the 50-300 ohms' worth of Rseries in most diodes will
    trash the SNR--there's not much use in a 300-pV/sqrt(Hz) TIA if the
    diode itself contributes way over a nanovolt.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 15:49:30 2024
    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak. I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    You don't need a bootstrap at 10 kHz, but a sufficiently carefully
    designed DC restore loop can help sometimes. A badly designed one will
    trash the SNR. At low frequency, the only way to make a quiet current
    source is to put a large voltage across a large resistor. I usually do
    that in the emitter circuit of a BJT, to get higher Zout, but you can
    also do it barefoot.

    The thing is, you're going to be dominated by the shot noise of the DC
    restore current unless its resistor is much larger than the feedback
    resistor of the TIA. (At high frequency you can use filtering tricks,
    but not easily at 10 kHz.) Since the DC restore is going to have the
    same supply headroom as the TIA, it really doesn't help.

    If you pick the TIA's feedback resistance so that the IR signal produces
    50 mV of output, you're in the shot noise limit, at least in the dark.
    However, since the sunlight's shot noise is going to be the limit most
    of the time, just pick a feedback resistor so the TIA nearly rails at
    the worst-case background light level, and see if that gives you enough
    SNR to be going on with. If so, AC-couple it into the second stage and
    you're done.

    If not, you need to reduce the background with a better filter, or
    (better) reduce the field of view by using a lens on the receiver, and
    increase the signal by using one on the transmitter. You win by the
    square of the angular magnification, which can be a fairly startling number.

    Either way, you need to control your detection bandwidth to something reasonable, and remember that LP filter to get rid of the noise peak!

    Cheers

    Phil Hobbs


    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Mon Oct 28 14:10:59 2024
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak. I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low >component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    Put the two inductors close together. They will see mostly the same
    mag fields, so a couple of resistors added somewhere will cancel the
    pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    TV remotes work if you bounce the light off the ceiling in a well-lit
    room.

    But the acoustic approach would be better. Omni MEMS microphones have
    built-in amps and cost 20 cents.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Phil Hobbs on Tue Oct 29 00:31:41 2024
    On 28-10-2024 20:16, Phil Hobbs wrote:
    On 2024-10-27 08:20, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:05, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too
    noisy,
    not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise,
    specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will
    help more. The real win is reducing the FOV with lenses as well as
    baffles,
    tubes, and so on.


    I have tried to search for optical filters. Where would one get those?

    700-nm plastic longpass filter material comes in sheets.  You can get smallish chunks of it on the jungle website and various other emporia.

    Fancier things, such as narrowish bandpasses and custom wavelengths,
    tend to be glass and quite a lot more expensive.  I usually get those
    from Omega Optical, but there are European suppliers as well.

    For this use, a regular 700-nmm plastic longpass will get rid of most of
    the daylight, which is what you want.  You can also get photodiodes with
    the filter material included, e.g. the ever-popular BPW34F.


    Great recommendations, thanks. I have purchased a bunch of the BPW34F.


    Baffles and tubes, we can do ourselves, any guideline on the best
    surface of the inner tube?

    Regular old flat black paint.  But a lens on the transmitter will be the biggest win.


    Check out the Hamamatsu S6968–super good medicine.


    Looks like a very big die. Is that the main reason to use that one, to
    get better sensitivity?

    It has very low capacitance for its area, it has a lens to increase the detection area, and (crucially for my uses, which are generally at
    higher frequency) it has very very low series resistance.

    The series resistance of the diode contributes Johnson noise that can't
    be removed by bootstrapping.  You don't care too much at 10 kHz, but at higher frequency the 50-300 ohms' worth of Rseries in most diodes will
    trash the SNR--there's not much use in a 300-pV/sqrt(Hz) TIA if the
    diode itself contributes way over a nanovolt.

    So in fact the devil is in the detail. I have not done higher
    performance optics before, so riding on the learning curve.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to piglet on Tue Oct 29 00:39:03 2024
    On 28-10-2024 13:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>> current, frequency modulated so that the receiver can ignore the effect >>>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>> lower, but does reduced the effective range of the system during >>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>> photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>> the gain would be close to zero for the stage after. I would then still >>>>> need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single
    transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver
    on the robot and two emitters on the docking station, a bit like aircraft
    VOR



    Yeah, that is better. Then alternating switching between the two
    emitters at separate frequencies makes it easier to do detection on the reciever side. Separate envelope detection finds the midpoint when the
    two lopes are equal. Requires matching of the emitter diodes. Can be
    done in production or adding a receiver/monitor photodiode at the
    location of the 2 emitters

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to klauskvik@hotmail.com on Mon Oct 28 19:29:00 2024
    On Mon, 28 Oct 2024 11:08:50 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 21:39, Joe Gwinn wrote:
    On Sun, 27 Oct 2024 10:49:27 -0700, john larkin <JL@gct.com> wrote:

    On Sun, 27 Oct 2024 13:42:27 +0100, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/ >>>>>>>> Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>> the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    A photodiode won't saturate as long as it has a few volts of DC across
    it. It might melt if there's no current limiting.


    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:

    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    The LC tank combines background light rejection and bandpass filtering
    and has high signal gain, with two parts.

    I think there are photodiodes with colored plastic, essentially a
    cheap optical bandpass filter. Used in TV remote receivers.

    The windows in TVs may be optical bandpass filters too. They work with
    very little signal from the remote, in high room light.

    To this I would add a trick. We know something very useful about the
    10 KHz modulation, its exact frequency, given that it is (or can be)
    generated electronically, and thus its frequency is ultimately
    controlled by a logic-clock crystal oscillator.

    So feed the amplified signal from the 10 KHz LC tank to a I+Q homodyne
    circuit, filter to pass signals from DC to a 10 Hz and compute the
    magnitude of the received signal - this is used for figuring out the
    direction to the docking station.

    Very nice, sort of like for lock-in detection, I have done that before,
    works great. Would take the tolerances out of the passive components.

    Yes, it is a form of lock-in detection, adapted to the lack of phase
    data, other than to know that it changes slowly.

    But there is another issue, interference from artificial light, such
    as streetlamps, at dawn and dusk. Many streetlamps are strongly
    modulated at a harmonic of the local prime power frequency, 50 Hz or
    60 Hz. Also, the receiver itself will have a noise floor that is
    essentially constant random noise.

    A classic remedy is correlated double sampling (CDS), where the sample
    period is exactly one tenth of a second in duration, into which an
    integral number of power cycles will fit exactly, and so will
    integrate to zero.

    Originally, CDS modulated the transmitter to alternate between on and
    off, so external light would fall in both odd and even numbered
    samples, while real data would only fall in one set of samples. Here
    the TX runs continuously, and it would be a nuisance to synchronize
    it, so we need a way to do the same in the RX units.

    The simplest approach would be to receive at two modulation
    frequencies, 10 KHz and say 11 KHz, alternating between them. Only
    the 10 KHz will have data, while both frequencies will have system
    noise and power-frequency modulated stray light.

    There are two identical integrators and a switch. The odd-numbered
    cycles go into the first integrator and the even-numbered cycles go to
    the second integrator. These integrator are leaky. One reports their difference as the 10 KHz modulation strength.

    There are many schemes like this that could work.

    Joe Gwinn

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Joe Gwinn on Tue Oct 29 00:34:49 2024
    On 29-10-2024 00:29, Joe Gwinn wrote:
    On Mon, 28 Oct 2024 11:08:50 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 21:39, Joe Gwinn wrote:
    On Sun, 27 Oct 2024 10:49:27 -0700, john larkin <JL@gct.com> wrote:

    On Sun, 27 Oct 2024 13:42:27 +0100, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    On 27-10-2024 13:40, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/ >>>>>>>>> Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The >>>>>>>>> spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>> the gain would be close to zero for the stage after. I would then >>>>>>> still need to be sure the photodiode is never saturated by ambient light.

    A photodiode won't saturate as long as it has a few volts of DC across >>>> it. It might melt if there's no current limiting.


    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....

    Like this:

    https://electronics.stackexchange.com/questions/416184/how-does-this-op-amp-photodiode-circuit-behave

    The LC tank combines background light rejection and bandpass filtering >>>> and has high signal gain, with two parts.

    I think there are photodiodes with colored plastic, essentially a
    cheap optical bandpass filter. Used in TV remote receivers.

    The windows in TVs may be optical bandpass filters too. They work with >>>> very little signal from the remote, in high room light.

    To this I would add a trick. We know something very useful about the
    10 KHz modulation, its exact frequency, given that it is (or can be)
    generated electronically, and thus its frequency is ultimately
    controlled by a logic-clock crystal oscillator.

    So feed the amplified signal from the 10 KHz LC tank to a I+Q homodyne
    circuit, filter to pass signals from DC to a 10 Hz and compute the
    magnitude of the received signal - this is used for figuring out the
    direction to the docking station.

    Very nice, sort of like for lock-in detection, I have done that before,
    works great. Would take the tolerances out of the passive components.

    Yes, it is a form of lock-in detection, adapted to the lack of phase
    data, other than to know that it changes slowly.

    But there is another issue, interference from artificial light, such
    as streetlamps, at dawn and dusk. Many streetlamps are strongly
    modulated at a harmonic of the local prime power frequency, 50 Hz or
    60 Hz. Also, the receiver itself will have a noise floor that is
    essentially constant random noise.

    A classic remedy is correlated double sampling (CDS), where the sample
    period is exactly one tenth of a second in duration, into which an
    integral number of power cycles will fit exactly, and so will
    integrate to zero.


    The Keysight DMM had/has n powercycles filter, same idea.

    Originally, CDS modulated the transmitter to alternate between on and
    off, so external light would fall in both odd and even numbered
    samples, while real data would only fall in one set of samples. Here
    the TX runs continuously, and it would be a nuisance to synchronize
    it, so we need a way to do the same in the RX units.

    The simplest approach would be to receive at two modulation
    frequencies, 10 KHz and say 11 KHz, alternating between them. Only
    the 10 KHz will have data, while both frequencies will have system
    noise and power-frequency modulated stray light.

    There are two identical integrators and a switch. The odd-numbered
    cycles go into the first integrator and the even-numbered cycles go to
    the second integrator. These integrator are leaky. One reports their difference as the 10 KHz modulation strength.

    There are many schemes like this that could work.

    Joe Gwinn

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Phil Hobbs on Tue Oct 29 00:44:18 2024
    On 28-10-2024 20:49, Phil Hobbs wrote:
    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you.  It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak.  I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering.  A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    You don't need a bootstrap at 10 kHz, but a sufficiently carefully
    designed DC restore loop can help sometimes.  A badly designed one will trash the SNR. At low frequency, the only way to make a quiet current
    source is to put a large voltage across a large resistor.  I usually do
    that in the emitter circuit of a BJT, to get higher Zout, but you can
    also do it barefoot.

    The thing is, you're going to be dominated by the shot noise of the DC restore current unless its resistor is much larger than the feedback
    resistor of the TIA.  (At high frequency you can use filtering tricks,
    but not easily at 10 kHz.)  Since the DC restore is going to have the
    same supply headroom as the TIA, it really doesn't help.

    If you pick the TIA's feedback resistance so that the IR signal produces
    50 mV of output, you're in the shot noise limit, at least in the dark. However, since the sunlight's shot noise is going to be the limit most
    of the time, just pick a feedback resistor so the TIA nearly rails at
    the worst-case background light level, and see if that gives you enough
    SNR to be going on with.  If so, AC-couple it into the second stage and you're done.

    If not, you need to reduce the background with a better filter, or
    (better) reduce the field of view by using a lens on the receiver, and increase the signal by using one on the transmitter.  You win by the
    square of the angular magnification, which can be a fairly startling
    number.

    Either way, you need to control your detection bandwidth to something reasonable, and remember that LP filter to get rid of the noise peak!


    Sounds like I should hire you in a reviewer, if I get stuck :-)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to john larkin on Tue Oct 29 00:49:00 2024
    On 28-10-2024 20:05, john larkin wrote:
    On Mon, 28 Oct 2024 11:11:38 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 27-10-2024 18:56, john larkin wrote:
    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard
    Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>: >>>>
    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat.
    Cheap electret mikes? or modify some ebay 1 dolalr distance sensors... >>>> can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could
    be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Could also be done with a chirp and auto-correlation, although this does
    not use the phase, but a beacon reference instead

    Could that tell the direction of the mother ship?


    If the chirp arrives at the same time at each mike, the robot is on the
    right path, If one is delayed, the robot eases into the that direction

    Three or four omni mems microphones could tell the robot which
    direction to go with full 360 degree coverage.

    Maybe even estimate range.

    I did a design based on a rectangular wire loop, with 4 pickup coils in
    a star formation. That configuration could tell the robot how much it
    was off directly without using a search pattern.

    But, they do not want that, all though it performance very good.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Don Y on Tue Oct 29 00:52:43 2024
    On 28-10-2024 13:01, Don Y wrote:
    On 10/28/2024 3:17 AM, Klaus Vestergaard Kragelund wrote:
    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>> detectors on the robot detects the beam and lets the robot
    navigate towards the target. The working distance is a couple of
    meters.

    Can the robot ALWAYS see the docking station?  What happens if an
    obstacle (wall?) comes between the two?

    Yes, we have RTK GPS to position it within a cm at a location right
    in front of the docking, 2 meters away.

    Then why can't you move to the GPS location of the dock with the
    same degree of accuracy?

    The docking station is typically in a shed, or close to a building
    where the GPS signal disappears.

    Ah, OK.

    Can either device (robot/dock) ever slip out of the shared plane?

    No, should be locked

    "Outdoors" (from below).  Presumably on pavement/concrete (not a "lawn") >>> that wouldn't have dips and bumps?

    It's moving on grass, and can have bumps etc, so for IR the lope needs
    to be perhaps 20degrees to avoid loss of signal

    And, presumably, they are short (time and space) transients?  *Faster*
    than the response time of the robots controls?


    Yes, the inner loop must be a lot faster than the control time of the
    robot, or it will oscillate ;-)

    I have become particularly fond of using cameras to interface with
    the real world.  Of course, it requires a bit more horsepower but
    seems to be able to overcome all of the issues that have crept up...

    That's also a solution we have been working on. The Worx Vision uses
    that

    https://eu.worx.com/da-dk/landroid/vision-technology/

    That is for a future version. Cameras can also be blinded, lenses
    needs to be cleaned etc

    Yes, but a camera can be "queried" to verify that it is functioning
    correctly:  "What do you see?  Is it THIS?"

    I test my cameras by storing previously viewed scenes to verify they
    are still "reasonably" intact.  Ideally, I would move something into
    the field of view but that requires additional capabilities.

    You, however, could move the robot (assuming IT has the eyes) and
    verify that the scene changes accordingly.

    Could be done. The guys in charge are worried with change of
    environment, so what happens when it snows heavily, fog or other
    surroundings changing effects.

    You extract salient "features" from the scene and use them.
    The robot doesn't need to be concerned about whether the ground is
    green, brown or white.  Or, if the shed is in shade, blanketed
    with snow, etc.

    E.g., I use them to "watch" the garage door rails (which have a specific shape) to see if any objects have come between the camera and the rails.
    (The rails define the plane that the garage door will occupy as
    it closes)  Of course, everything around the rails is highly variable
    as garages are notorious for clutter and dynamism.

    Another camera "watches" the mailbox by the road.  In addition to
    the surroundings changing, there can be pedestrian and vehicular
    traffic passing at any time.  In our case, it is illegal to
    drive while using a phone so folks often pull over to answer
    phone calls -- our mailbox is in a shaded area that seems to be
    highly desirable to such motorists-in-need.  But, *their*
    vehicles don't look like "mail trucks" so no chance of thinking that
    *they* are delivering our mail...

    As I said before, it is a really great "sensor"!  The downside is
    that you need resources to use it (your optical approach is likely
    possible with far less resources -- think of how robot vaccuum cleaners operate wrt their charging docks)


    Correct, all though high resolutionn cameraes are very cheap nowadays.
    And they have a Linux maching running the application SW, so adding a
    camera does not add much extra cost, just a camera interface IC.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 19:54:27 2024
    On 2024-10-28 19:31, Klaus Vestergaard Kragelund wrote:
    On 28-10-2024 20:16, Phil Hobbs wrote:
    On 2024-10-27 08:20, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:05, Phil Hobbs wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the
    effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>> point of the robot (2 meters away) than possible IR from sunlight,
    then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to
    zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?


    Phototransistors are horrible for that sort of job— too small, too
    noisy,
    not repeatable, for a start.

    It’s not signal/background you care about, it’s signal/noise,
    specifically
    the shot noise of the sunlight.

    An optical filter will help reject sunlight, and a bigger detector will >>>> help more. The real win is reducing the FOV with lenses as well as
    baffles,
    tubes, and so on.


    I have tried to search for optical filters. Where would one get those?

    700-nm plastic longpass filter material comes in sheets.  You can get
    smallish chunks of it on the jungle website and various other emporia.

    Fancier things, such as narrowish bandpasses and custom wavelengths,
    tend to be glass and quite a lot more expensive.  I usually get those
    from Omega Optical, but there are European suppliers as well.

    For this use, a regular 700-nmm plastic longpass will get rid of most
    of the daylight, which is what you want.  You can also get photodiodes
    with the filter material included, e.g. the ever-popular BPW34F.


    Great recommendations, thanks. I have purchased a bunch of the BPW34F.


    Baffles and tubes, we can do ourselves, any guideline on the best
    surface of the inner tube?

    Regular old flat black paint.  But a lens on the transmitter will be
    the biggest win.


    Check out the Hamamatsu S6968–super good medicine.


    Looks like a very big die. Is that the main reason to use that one,
    to get better sensitivity?

    It has very low capacitance for its area, it has a lens to increase
    the detection area, and (crucially for my uses, which are generally at
    higher frequency) it has very very low series resistance.

    The series resistance of the diode contributes Johnson noise that
    can't be removed by bootstrapping.  You don't care too much at 10 kHz,
    but at higher frequency the 50-300 ohms' worth of Rseries in most
    diodes will trash the SNR--there's not much use in a 300-pV/sqrt(Hz)
    TIA if the diode itself contributes way over a nanovolt.

    So in fact the devil is in the detail. I have not done higher
    performance optics before, so riding on the learning curve.

    It's a good ride. ;)

    The really good thing is that all the relevant noise sources can be
    calculated really easily from first principles.

    If you calculate using just the shot noise and Johnson noise formulas,
    you'll get the right SNR answer to within a fraction of a dB. So if you
    figure out what the low- and high-background limits are, you can figure
    out what the performance will be in a few minutes.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to piglet on Mon Oct 28 20:08:45 2024
    On 2024-10-27 18:59, piglet wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single transistor or op amp could take the role of inductor.

    Hard to do without trashing the noise, at least in dim light. (In
    really bright light the shot noise of the sunlight photocurrent can
    easily swamp everything.)

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 17:12:54 2024
    On 10/28/2024 4:52 PM, Klaus Vestergaard Kragelund wrote:
    As I said before, it is a really great "sensor"!  The downside is
    that you need resources to use it (your optical approach is likely
    possible with far less resources -- think of how robot vaccuum cleaners
    operate wrt their charging docks)

    Correct, all though high resolutionn cameraes are very cheap nowadays. And they
    have a Linux maching running the application SW, so adding a camera does not add much extra cost, just a camera interface IC.

    But, you need enough MIPS to process the video!

    As for cameras, you have three options, there:
    - RS170-ish
    - USB
    - Network

    I prefer the last (though likely most costly) as there is less
    likelihood of hidden protocol gotchas.

    I have a (toy?) robot application where the robots are controlled
    externally based on observations from sensors in their environment.
    It was considerably easier than equipping the robots with the
    sensors and processing ability (how do you reliably sense that
    you are navigating as intended in a given arena?)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Wanderer on Tue Oct 29 00:55:02 2024
    On 28-10-2024 11:39, Wanderer wrote:
    It's Burr-Brown(I'm old) OPT201.

    https://electronix.org.ru/datasheet/Burr-Brown/AB-061%20-%20OPT201%20to%20reject%20ambient%20light.pdf

    Nice

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to piglet on Mon Oct 28 20:19:25 2024
    On 2024-10-28 08:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>> current, frequency modulated so that the receiver can ignore the effect >>>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>> lower, but does reduced the effective range of the system during >>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>> photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>> the gain would be close to zero for the stage after. I would then still >>>>> need to be sure the photodiode is never saturated by ambient light.

    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single
    transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver
    on the robot and two emitters on the docking station, a bit like aircraft
    VOR

    Or like certain radio navigation systems popular in Western Europe, 80
    or so years ago. ;)

    That's a good example of Horace Darwin's maxim, "Always try it the other
    way round", quoted in "Instruments and Experiences" by R. V. Jones.

    Jones is one of my technical heroes, and was instrumental in defeating a
    couple of the aforementioned navigation systems, specifically
    "Knickebein" and "X-Geraet", as explained in his book, "The Wizard War" (entitled "Most Secret War" in the UK). Horace Darwin was a grandson of Charles Darwin, and a colleague of Jones's at Aberdeen after the war.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Mon Oct 28 20:31:14 2024
    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak. I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low
    component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap >>from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz
    on up. I saw your VFD EMI filters at your Otis St shop. ;)


    Put the two inductors close together. They will see mostly the same
    mag fields, so a couple of resistors added somewhere will cancel the
    pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC
    couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit
    room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make
    the apparent direction of the acoustic source move by 3 mrad.

    Cheers

    Phil Hobbs



    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to Klaus Vestergaard Kragelund on Mon Oct 28 20:33:53 2024
    On 2024-10-28 19:44, Klaus Vestergaard Kragelund wrote:
    On 28-10-2024 20:49, Phil Hobbs wrote:
    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the
    effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>> point of the robot (2 meters away) than possible IR from sunlight,
    then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/
    Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to
    zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long
    as DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient
    light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you.  It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak.  I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low
    component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such
    as LC or *especially* gyrator filtering.  A large inductor is a
    disaster in a TIA, because if it doesn't cause instability, it'll
    still pick up crap from every VF motor drive on the block, and deposit
    it right into the summing junction, where you really really don't want
    it.

    You don't need a bootstrap at 10 kHz, but a sufficiently carefully
    designed DC restore loop can help sometimes.  A badly designed one
    will trash the SNR. At low frequency, the only way to make a quiet
    current source is to put a large voltage across a large resistor.  I
    usually do that in the emitter circuit of a BJT, to get higher Zout,
    but you can also do it barefoot.

    The thing is, you're going to be dominated by the shot noise of the DC
    restore current unless its resistor is much larger than the feedback
    resistor of the TIA.  (At high frequency you can use filtering tricks,
    but not easily at 10 kHz.)  Since the DC restore is going to have the
    same supply headroom as the TIA, it really doesn't help.

    If you pick the TIA's feedback resistance so that the IR signal
    produces 50 mV of output, you're in the shot noise limit, at least in
    the dark. However, since the sunlight's shot noise is going to be the
    limit most of the time, just pick a feedback resistor so the TIA
    nearly rails at the worst-case background light level, and see if that
    gives you enough SNR to be going on with.  If so, AC-couple it into
    the second stage and you're done.

    If not, you need to reduce the background with a better filter, or
    (better) reduce the field of view by using a lens on the receiver, and
    increase the signal by using one on the transmitter.  You win by the
    square of the angular magnification, which can be a fairly startling
    number.

    Either way, you need to control your detection bandwidth to something
    reasonable, and remember that LP filter to get rid of the noise peak!


    Sounds like I should hire you in a reviewer, if I get stuck :-)

    ;)

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC / Hobbs ElectroOptics
    Optics, Electro-optics, Photonics, Analog Electronics
    Briarcliff Manor NY 10510

    http://electrooptical.net
    http://hobbs-eo.com

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to Phil Hobbs on Tue Oct 29 15:20:58 2024
    On 29/10/2024 11:19 am, Phil Hobbs wrote:
    On 2024-10-28 08:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    <snip>

    Of course they might be able to reverse the process and have one receiver
    on the robot and two emitters on the docking station, a bit like aircraft
    VOR

    Or like certain radio navigation systems popular in Western Europe, 80
    or so years ago. ;)

    That's a good example of Horace Darwin's maxim, "Always try it the other
    way round", quoted in "Instruments and Experiences" by R. V. Jones.

    Jones is one of my technical heroes, and was instrumental in defeating a couple of the aforementioned navigation systems, specifically
    "Knickebein" and "X-Geraet", as explained in his book, "The Wizard War" (entitled "Most Secret War" in the UK).  Horace Darwin was a grandson of Charles Darwin, and a colleague of Jones's at Aberdeen after the war.

    Horace Darwin - Charles Darwin's youngest son - founded Cambridge
    Instruments where I worked from 1982 to 1991. He died in 1928.

    https://en.wikipedia.org/wiki/Horace_Darwin

    One of the people I worked with had seen his WW1 patent applications,
    most of which involved a lot of string, when the company history files
    were being moved to a new site.

    I actually knew one of Charles Darwin's grandsons, when he was a
    professor at Sussex University. If there was a Horace Darwin in his
    generation, Google doesn't know about it.

    https://www.sussex.ac.uk/profiles/652

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Bill Sloman@21:1/5 to Phil Hobbs on Tue Oct 29 15:31:11 2024
    On 29/10/2024 6:49 am, Phil Hobbs wrote:
    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR
    detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>> to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then >>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up >>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The
    spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then
    still need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you.  It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak.  I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low component-value sensitivity, and is super simple.

    If you can afford a little gain in the two pole Sallen-Key filter stage,
    you can use the gain to tune for a critically damped response with equal
    value capacitors, which can be from the same batch, which makes
    procurement a lot easier.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering.  A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    You don't need a bootstrap at 10 kHz, but a sufficiently carefully
    designed DC restore loop can help sometimes.  A badly designed one will trash the SNR. At low frequency, the only way to make a quiet current
    source is to put a large voltage across a large resistor.  I usually do
    that in the emitter circuit of a BJT, to get higher Zout, but you can
    also do it barefoot.

    The thing is, you're going to be dominated by the shot noise of the DC restore current unless its resistor is much larger than the feedback
    resistor of the TIA.  (At high frequency you can use filtering tricks,
    but not easily at 10 kHz.)  Since the DC restore is going to have the
    same supply headroom as the TIA, it really doesn't help.

    If you pick the TIA's feedback resistance so that the IR signal produces
    50 mV of output, you're in the shot noise limit, at least in the dark. However, since the sunlight's shot noise is going to be the limit most
    of the time, just pick a feedback resistor so the TIA nearly rails at
    the worst-case background light level, and see if that gives you enough
    SNR to be going on with.  If so, AC-couple it into the second stage and you're done.

    Or spend around a thousand dollars on a really narrow band interference
    filter that only lets through your laser wavelength, and blocks sunlight.

    An expensive solution, but hard to beat.

    If not, you need to reduce the background with a better filter, or
    (better) reduce the field of view by using a lens on the receiver, and increase the signal by using one on the transmitter.  You win by the
    square of the angular magnification, which can be a fairly startling
    number.

    Either way, you need to control your detection bandwidth to something reasonable, and remember that LP filter to get rid of the noise peak!

    --
    Bill Sloman, Sydney

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to Klaus Vestergaard Kragelund on Tue Oct 29 11:20:23 2024
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    [...]

    If the chirp arrives at the same time at each mike, the robot is on the
    right path, If one is delayed, the robot eases into the that direction

    If one of the chirps has been reflected from a distant hard surface the
    long delay could interfere with the next pulse. Something like that
    happened to an early-warning radar sytem when the moon rose and
    reflected long-delayed pulses.

    A slow pulse rate or a variable one would overcome this.


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Liz Tuddenham on Tue Oct 29 05:02:33 2024
    On 10/29/2024 4:20 AM, Liz Tuddenham wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    [...]

    If the chirp arrives at the same time at each mike, the robot is on the
    right path, If one is delayed, the robot eases into the that direction

    If one of the chirps has been reflected from a distant hard surface the
    long delay could interfere with the next pulse. Something like that
    happened to an early-warning radar sytem when the moon rose and
    reflected long-delayed pulses.

    A slow pulse rate or a variable one would overcome this.

    ISTR Polaroid's ultrasonic ranging kit; the transducer was driven
    with pulses in a fixed pattern at four distinct frequencies.
    This helped the receiver determine the "envelope" for a single burst.

    In LORAN, the carrier was modulated with a specific envelope
    (as well as a pulse code pattern) to let the receiver identify
    a specific reference point on the carrier. (because multiple
    signal sources could be present in a given geographical area)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Don Y@21:1/5 to Don Y on Tue Oct 29 06:04:30 2024
    On 10/29/2024 5:02 AM, Don Y wrote:
    In LORAN, the carrier was modulated with a specific envelope
    (as well as a pulse code pattern) to let the receiver identify
    a specific reference point on the carrier.  (because multiple
    signal sources could be present in a given geographical area)

    Actually, an audio frequency version of LORAN could work in this
    application! But, would require more "set up" of the arena.

    Three transmitters would be placed at fixed locations (there are
    some concerns over the optimal geometry but there is also a lot
    of variability tolerated). The "robot" would have a single
    omnidirectional receiver (microphone/ultrasonic transducer, etc).

    The location of the base would be known a priori (along with the
    locations of the three transmitters).

    One transmitter would be designated as the "Master". It would
    emit an omnidirectional pulse "periodically". Each of the remaining
    two transmitters would emit pulses at fixed delays from that master
    pulse. In LORAN, this is done by *receiving* the master's pulse
    (which takes time to arrive proportional to the distance from the
    master) and adding a fixed "coding delay". But, on a small physical
    scale, this could be accomplished with any other synchronization
    mechanism (including hard-wired).

    [Each of the other (two) stations ("slaves") has a different coding
    delay so the signals from the master and slaves arrive separated
    in time from each other.]

    The robot detects the master's pulse at a particular time. And, the
    pulses from the two slaves at some time after that.

    The difference, in time, between master and each slave defines
    a hyperbolic curve in 2D space. The intersection of the two
    curves (master-to-slave-1 and master-to-slave-2) defines the
    position of the robot in that space.

    At 1100ft/sec, one could resolve a foot with a crude timebase of
    1KHz. If you can count 10KHz, you can resolve an inch. 100KHz
    and you're at an eighth of an inch. (there is some hand-waving, here,
    as there is a geometric dilution of precision, depending on
    where on each hyperbola the robot happens to be)

    With positional information, you could actually describe a *specific*
    path to be followed to the base to avoid fixed obstacles in the
    arena.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Tue Oct 29 07:45:48 2024
    On Tue, 29 Oct 2024 00:49:00 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 28-10-2024 20:05, john larkin wrote:
    On Mon, 28 Oct 2024 11:11:38 +0100, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    On 27-10-2024 18:56, john larkin wrote:
    On Sun, 27 Oct 2024 09:03:20 GMT, Jan Panteltje <alien@comet.invalid>
    wrote:

    On a sunny day (Sun, 27 Oct 2024 02:19:14 +0200) it happened Klaus Vestergaard
    Kragelund <klauskvik@hotmail.com> wrote in <vfk0u0$3u9en$1@dont-email.me>:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.


    I use a cheap camera module to track a light source in H and V direction, and just a simple Microchip PIC : for processing
    It can, with some added code, track object forms too, like a cross or maybe a big character.
    panteltje.nl/pub/horizontal_IR_target_tracking_4686.avi
    those camara modulea are IR sensitive to some extend, sometimes you can remove the IR filter from such modules.
    It may be a bit of overkill for your application, but OTOH it can do a lot more.
    Mainly designed to detect and follow jet exhaust..
    You could uee utrasonics too, maybe even simpler, no sun problem, like a bat.
    Cheap electret mikes? or modify some ebay 1 dolalr distance sensors... >>>>> can be used for anti-collision too.



    Right. A sonic scheme could measure the phase between two mikes to
    determine the direction of the source with high resolution. That could >>>> be an analog multiplier or a bit of code. The amplitudes would be
    useful too.

    One could compute direction, distance, and velocity almost for free.

    No problem with sunlight!

    Could also be done with a chirp and auto-correlation, although this does >>> not use the phase, but a beacon reference instead

    Could that tell the direction of the mother ship?


    If the chirp arrives at the same time at each mike, the robot is on the
    right path, If one is delayed, the robot eases into the that direction

    Three or four omni mems microphones could tell the robot which
    direction to go with full 360 degree coverage.

    Maybe even estimate range.

    I did a design based on a rectangular wire loop, with 4 pickup coils in
    a star formation. That configuration could tell the robot how much it
    was off directly without using a search pattern.

    But, they do not want that, all though it performance very good.

    Life would be so much better without customers.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Tue Oct 29 07:43:55 2024
    On Mon, 28 Oct 2024 20:19:25 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 08:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/ >>>>>>>> Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>> the gain would be close to zero for the stage after. I would then still >>>>>> need to be sure the photodiode is never saturated by ambient light. >>>>>>
    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single >>>> transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver
    on the robot and two emitters on the docking station, a bit like aircraft
    VOR

    Or like certain radio navigation systems popular in Western Europe, 80
    or so years ago. ;)

    That's a good example of Horace Darwin's maxim, "Always try it the other
    way round", quoted in "Instruments and Experiences" by R. V. Jones.

    Jones is one of my technical heroes, and was instrumental in defeating a >couple of the aforementioned navigation systems, specifically
    "Knickebein" and "X-Geraet", as explained in his book, "The Wizard War" >(entitled "Most Secret War" in the UK). Horace Darwin was a grandson of >Charles Darwin, and a colleague of Jones's at Aberdeen after the war.

    Cheers

    Phil Hobbs

    https://www.amazon.com/Instruments-Experiences-Measurement-Instrument-Technology/dp/047191763X

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Tue Oct 29 16:03:12 2024
    john larkin <JL@gct.com> wrote:
    On Mon, 28 Oct 2024 20:19:25 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 08:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/ >>>>>>>>> Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>> the gain would be close to zero for the stage after. I would then still >>>>>>> need to be sure the photodiode is never saturated by ambient light. >>>>>>>
    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single >>>>> transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver >>> on the robot and two emitters on the docking station, a bit like aircraft >>> VOR

    Or like certain radio navigation systems popular in Western Europe, 80
    or so years ago. ;)

    That's a good example of Horace Darwin's maxim, "Always try it the other
    way round", quoted in "Instruments and Experiences" by R. V. Jones.

    Jones is one of my technical heroes, and was instrumental in defeating a
    couple of the aforementioned navigation systems, specifically
    "Knickebein" and "X-Geraet", as explained in his book, "The Wizard War"
    (entitled "Most Secret War" in the UK). Horace Darwin was a grandson of
    Charles Darwin, and a colleague of Jones's at Aberdeen after the war.

    Cheers

    Phil Hobbs

    https://www.amazon.com/Instruments-Experiences-Measurement-Instrument-Technology/dp/047191763X




    Cheap at twice the price!

    It’s a unique book—a collection of Jones’s groundbreaking papers on things
    like measuring the ether drag on light in a moving dielectric, which would
    be a niche interest except that each one is paired with an essay of about
    equal length explaining how the measurement was done.

    Those pieces are of lasting value—they’re confidential in tone, including the inventions required, the blind alleys, and very often, how somebody
    made a big difference with a piece of hard-won advice, like that remark of Darwin’s.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Tue Oct 29 09:44:47 2024
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>> duty cycle. Low duty cycle to be able to drive the LED with high
    current, frequency modulated so that the receiver can ignore the effect >>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at >>>>>> sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>> lower, but does reduced the effective range of the system during
    fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The
    photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still >>>> need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak. I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low
    component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in >>> a TIA, because if it doesn't cause instability, it'll still pick up crap >>>from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz
    on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same
    mag fields, so a couple of resistors added somewhere will cancel the
    pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit
    room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have
    built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make
    the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve
    the path.

    You're an optics guy, so maybe don't like the sound thing.


    Cheers

    Phil Hobbs

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Tue Oct 29 17:02:02 2024
    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>> towards the target. The working distance is a couple of meters.

    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>> current, frequency modulated so that the receiver can ignore the effect >>>>>>> of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then >>>>>>> that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this:

    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero >>>>>>> in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>> lower, but does reduced the effective range of the system during >>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>> photodiode could have +DC on one end and the other end can hit a
    parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>> the gain would be close to zero for the stage after. I would then still >>>>> need to be sure the photodiode is never saturated by ambient light.

    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that.
    You only need enough bias to ensure linear operation at high current,
    maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak. I usually use a two-pole Sallen-Key
    with equal resistor values, which has predictable gain (1.00) and low
    component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as >>>> LC or *especially* gyrator filtering. A large inductor is a disaster in >>>> a TIA, because if it doesn't cause instability, it'll still pick up crap >>>> from every VF motor drive on the block, and deposit it right into the
    summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz
    on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same
    mag fields, so a couple of resistors added somewhere will cancel the
    pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC
    couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit
    room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have
    built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make
    the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve
    the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science project than the LED approach. )


    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Tue Oct 29 10:26:05 2024
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and >>>>>>>> to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the >>>>>>>> signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up >>>>>>>> the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>> the gain would be close to zero for the stage after. I would then still >>>>>> need to be sure the photodiode is never saturated by ambient light. >>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or
    measure the photocurrent from direct sunlight and design around that. >>>>> You only need enough bias to ensure linear operation at high current, >>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the
    nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as >>>>> LC or *especially* gyrator filtering. A large inductor is a disaster in >>>>> a TIA, because if it doesn't cause instability, it'll still pick up crap >>>>> from every VF motor drive on the block, and deposit it right into the >>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz
    on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same
    mag fields, so a couple of resistors added somewhere will cancel the
    pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC
    couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit
    room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have
    built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make
    the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve
    the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science >project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to jrwalliker@gmail.com on Tue Oct 29 11:27:31 2024
    On Tue, 29 Oct 2024 17:31:03 +0000, John R Walliker
    <jrwalliker@gmail.com> wrote:

    On 29/10/2024 17:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as >>>>>>> LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>>>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve
    the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science
    project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    You would need more than two microphones to get unambiguous results.

    John

    It would be better than two photodiodes in black tubes.

    Three or four mikes would give 360 degree sensing.

    As I understood the problem, the robot is probably pointing at the
    mother ship, and just needs to be guided the final few feet.

    So simple. Some engineers don't like simple.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Tue Oct 29 20:00:32 2024
    john larkin <jl@glen--canyon.com> wrote:
    On Tue, 29 Oct 2024 17:31:03 +0000, John R Walliker
    <jrwalliker@gmail.com> wrote:

    On 29/10/2024 17:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>>>>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I donÂ’t necessarily dislike the sound idea, but itÂ’s more of a science >>>> project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    You would need more than two microphones to get unambiguous results.

    John

    It would be better than two photodiodes in black tubes.

    Maybe so. Depends on the numbers.


    Three or four mikes would give 360 degree sensing.

    As I understood the problem, the robot is probably pointing at the
    mother ship, and just needs to be guided the final few feet.

    So simple. Some engineers don't like simple.

    Some of them actually have to build the gizmo that we’re all busily opining about.
    ;)

    Cheers

    Phil Hobbs


    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to Klaus Vestergaard Kragelund on Tue Oct 29 19:59:10 2024
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking station.

    It sounds as though the problem could be solved easily and reliably with
    a VLF magnetic field, rather than light. Something along the lines of
    the Lorenz blind landing beacon. By using dot-dash modulation, the
    receiver would know which side of the centre line it was on.

    The only problem would be convincing your client that it wasn't radio -
    but that sounds like a much easier problem than all the solutions so far suggested.

    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Tue Oct 29 15:45:42 2024
    On Tue, 29 Oct 2024 20:00:32 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Tue, 29 Oct 2024 17:31:03 +0000, John R Walliker
    <jrwalliker@gmail.com> wrote:

    On 29/10/2024 17:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters. >>>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight. >>>>>>>>>>>>
    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during >>>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common >>>>>>>> switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor. >>>>>> Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again >>>>>>>> canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don?t necessarily dislike the sound idea, but it?s more of a science >>>>> project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    You would need more than two microphones to get unambiguous results.

    John

    It would be better than two photodiodes in black tubes.

    Maybe so. Depends on the numbers.


    Three or four mikes would give 360 degree sensing.

    As I understood the problem, the robot is probably pointing at the
    mother ship, and just needs to be guided the final few feet.

    So simple. Some engineers don't like simple.

    Some of them actually have to build the gizmo that we’re all busily opining >about.
    ;)

    Cheers

    Phil Hobbs

    It's simple: Just do what I say.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to john larkin on Tue Oct 29 23:55:04 2024
    On 29-10-2024 19:27, john larkin wrote:
    On Tue, 29 Oct 2024 17:31:03 +0000, John R Walliker
    <jrwalliker@gmail.com> wrote:

    On 29/10/2024 17:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>>>>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science
    project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    You would need more than two microphones to get unambiguous results.

    John

    It would be better than two photodiodes in black tubes.

    Three or four mikes would give 360 degree sensing.

    As I understood the problem, the robot is probably pointing at the
    mother ship, and just needs to be guided the final few feet.

    So simple. Some engineers don't like simple.

    This one cost just less than 2USD, goes to 80kHz:

    https://www.st.com/resource/en/datasheet/imp23absu.pdf

    But, the S/N is only 64dB. I don't see how you can do averaging, no
    access to the source. It would need to acquire continuously, doing FFT
    to detect the chirp. Would need to add filter to remove noise from surroundings, and it's own motors.

    Adding them on a PCB would could be tricky, since reflections still is a
    major hassle.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to Liz Tuddenham on Tue Oct 29 23:59:21 2024
    On 29-10-2024 20:59, Liz Tuddenham wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    It sounds as though the problem could be solved easily and reliably with
    a VLF magnetic field, rather than light. Something along the lines of
    the Lorenz blind landing beacon. By using dot-dash modulation, the
    receiver would know which side of the centre line it was on.

    The only problem would be convincing your client that it wasn't radio -
    but that sounds like a much easier problem than all the solutions so far suggested.

    I did look into that, but did not go deeper.

    The Lorenz beacon was very ingenious.

    The solution with a rectangular loop in the base of the docking station
    worked well, but the client doesn't want that.

    Maybe it's time to convince him to look at other solutions again :-)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to john larkin on Wed Oct 30 00:02:34 2024
    On 29-10-2024 18:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking >>>>>>>>> station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in >>>>>>>>> the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the >>>>>>>>> point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam, >>>>>>>>> shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz >>>>>>>>> signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>> fog/rain. Probably that's why these system do not use 750nm

    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>> the gain would be close to zero for the stage after. I would then still >>>>>>> need to be sure the photodiode is never saturated by ambient light. >>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>> You only need enough bias to ensure linear operation at high current, >>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as >>>>>> LC or *especially* gyrator filtering. A large inductor is a disaster in >>>>>> a TIA, because if it doesn't cause instability, it'll still pick up crap >>>>>> from every VF motor drive on the block, and deposit it right into the >>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same
    mag fields, so a couple of resistors added somewhere will cancel the >>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make
    the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve
    the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science >> project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of surface-mout MEMS mikes on a PC board.

    The advantage of the photo diode solution, is that it's all analog, so
    can be build and tested quickly, without ordering a PCB

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Tue Oct 29 16:31:46 2024
    On Wed, 30 Oct 2024 00:02:34 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 29-10-2024 18:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as >>>>>>> LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light,
    which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>>>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve
    the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science
    project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    The advantage of the photo diode solution, is that it's all analog, so
    can be build and tested quickly, without ordering a PCB

    You can solder some wires onto a MEMS microphone.

    Optical: imagine that the docking station has a small vertical wall
    inside a cavity or equivalent. There's an LED set back on each side,
    so the robot sees one LED or the other as it moves side to side. The
    robot has a single photodiode staring ahead.

    Drive the two LEDs at different frequencies. Too far left, you will
    hear BEEP. Too far right, hear BOOP. Sort of like the old airplane
    landing thing.

    Looks promising with two LEDs and a business card.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Tue Oct 29 19:56:44 2024
    On Tue, 29 Oct 2024 23:55:04 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 29-10-2024 19:27, john larkin wrote:
    On Tue, 29 Oct 2024 17:31:03 +0000, John R Walliker
    <jrwalliker@gmail.com> wrote:

    On 29/10/2024 17:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters. >>>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight. >>>>>>>>>>>>
    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during >>>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common >>>>>>>> switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor. >>>>>> Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again >>>>>>>> canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science >>>>> project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    You would need more than two microphones to get unambiguous results.

    John

    It would be better than two photodiodes in black tubes.

    Three or four mikes would give 360 degree sensing.

    As I understood the problem, the robot is probably pointing at the
    mother ship, and just needs to be guided the final few feet.

    So simple. Some engineers don't like simple.

    This one cost just less than 2USD, goes to 80kHz:

    https://www.st.com/resource/en/datasheet/imp23absu.pdf

    But, the S/N is only 64dB. I don't see how you can do averaging, no
    access to the source. It would need to acquire continuously, doing FFT
    to detect the chirp. Would need to add filter to remove noise from >surroundings, and it's own motors.

    Digikey has mems mikes for 20 cents. They are pretty flat to 20 KHz.

    One would bandpass filter, same as you would with a photodiode.


    Adding them on a PCB would could be tricky, since reflections still is a >major hassle.

    Shouldn't be too difficult. Even reflections travel at the speed of
    sound.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Wed Oct 30 06:49:16 2024
    On a sunny day (Tue, 29 Oct 2024 20:00:32 -0000 (UTC)) it happened Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in <vfresv$1mp8a$1@dont-email.me>:

    john larkin <jl@glen--canyon.com> wrote:
    On Tue, 29 Oct 2024 17:31:03 +0000, John R Walliker
    <jrwalliker@gmail.com> wrote:

    On 29/10/2024 17:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters. >>>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight. >>>>>>>>>>>>
    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during >>>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common >>>>>>>> switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor. >>>>>> Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again >>>>>>>> canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I donÂ’t necessarily dislike the sound idea, but itÂ’s more of a science >>>>> project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    You would need more than two microphones to get unambiguous results.

    John

    It would be better than two photodiodes in black tubes.

    Maybe so. Depends on the numbers.


    Three or four mikes would give 360 degree sensing.

    As I understood the problem, the robot is probably pointing at the
    mother ship, and just needs to be guided the final few feet.

    So simple. Some engineers don't like simple.

    Some of them actually have to build the gizmo that we’re all busily opining >about.
    ;)


    Anybody made one yet that uses smell?

    Piece of pizza at the target (for humans),
    butterflies use the smell of honey
    Dogs? etc etc

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Vestergaard Kragelund@21:1/5 to john larkin on Wed Oct 30 09:45:42 2024
    On 30-10-2024 00:31, john larkin wrote:
    On Wed, 30 Oct 2024 00:02:34 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 29-10-2024 18:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common
    switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor.
    Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again
    canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account >>>>>> of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science
    project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    The advantage of the photo diode solution, is that it's all analog, so
    can be build and tested quickly, without ordering a PCB

    You can solder some wires onto a MEMS microphone.

    Optical: imagine that the docking station has a small vertical wall
    inside a cavity or equivalent. There's an LED set back on each side,
    so the robot sees one LED or the other as it moves side to side. The
    robot has a single photodiode staring ahead.

    Drive the two LEDs at different frequencies. Too far left, you will
    hear BEEP. Too far right, hear BOOP. Sort of like the old airplane
    landing thing.

    Looks promising with two LEDs and a business card.

    Yes, that's how the Luba does it:

    https://youtu.be/tKSR9LqHPDI?si=0V9nWtexG4yKP_wO&t=110

    I have shifted to that too, then only a single receiver is needed.

    On the topic of optics, some LIDAR system uses 940nm, since water
    absorption removes most of the sunlight interference:

    https://www.e-motec.net/wp-content/uploads/2022/02/10.png

    But, for this IR system, the power output is close to a million times
    lower than a LIDAR, and water absorbtion could reduce the beam strength
    from emitter to receiver if there's fog or rain.

    Would 940nm be a good choice for a IR system?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Liz Tuddenham@21:1/5 to Klaus Vestergaard Kragelund on Wed Oct 30 10:22:30 2024
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 29-10-2024 20:59, Liz Tuddenham wrote:
    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    It sounds as though the problem could be solved easily and reliably with
    a VLF magnetic field, rather than light. Something along the lines of
    the Lorenz blind landing beacon. By using dot-dash modulation, the receiver would know which side of the centre line it was on.

    The only problem would be convincing your client that it wasn't radio -
    but that sounds like a much easier problem than all the solutions so far suggested.

    I did look into that, but did not go deeper.

    The Lorenz beacon was very ingenious.

    The solution with a rectangular loop in the base of the docking station worked well, but the client doesn't want that.


    A ferrite rod aerial could be mounted so that it discriminated very
    clearly betweeen two transmitting loops and it could be located on the
    board with the electronics. You could wrap it in a cardboard tube to
    disguise it as a capacitor or something and tell the customer the system
    works by a newly-discovered magic principle.

    [I have made fake pre-war German capacitors to restore an historic Pathé projector and they were almost indistinguishable from the genuine
    article.]


    Maybe it's time to convince him to look at other solutions again :-)

    He is more of a problem than the electronics.


    --
    ~ Liz Tuddenham ~
    (Remove the ".invalid"s and add ".co.uk" to reply)
    www.poppyrecords.co.uk

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to klauskvik@hotmail.com on Wed Oct 30 08:09:58 2024
    On Wed, 30 Oct 2024 09:45:42 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 30-10-2024 00:31, john larkin wrote:
    On Wed, 30 Oct 2024 00:02:34 +0100, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    On 29-10-2024 18:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate
    towards the target. The working distance is a couple of meters. >>>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight. >>>>>>>>>>>>
    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Datasheet/OP505-506-535-705.pdf


    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/Spectrum%20with_out%20absorption.png


    Seems like 750nm would be better, since then the IR from the sun is
    lower, but does reduced the effective range of the system during >>>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but
    the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>>
    Just don't fry the photodiode in high light.


    So adding a resistance in series with the diode?

    Nah, the Johnson noise kills you. It's easier to just calculate or >>>>>>>>> measure the photocurrent from direct sunlight and design around that. >>>>>>>>> You only need enough bias to ensure linear operation at high current, >>>>>>>>> maybe a volt or so.

    You will want to put a filter in the second stage to get rid of the >>>>>>>>> nasty high-frequency noise peak. I usually use a two-pole Sallen-Key >>>>>>>>> with equal resistor values, which has predictable gain (1.00) and low >>>>>>>>> component-value sensitivity, and is super simple.

    Resist the temptation to do anything floral with the TIA stage, such as
    LC or *especially* gyrator filtering. A large inductor is a disaster in
    a TIA, because if it doesn't cause instability, it'll still pick up crap
    from every VF motor drive on the block, and deposit it right into the >>>>>>>>> summing junction, where you really really don't want it.

    Small shielded inductors are cheap, and 10 KHz is not a common >>>>>>>> switching frequency.

    VFDs put out large amounts of magnetic crap from the hundreds of hertz >>>>>>> on up. I saw your VFD EMI filters at your Otis St shop. ;)

    That was conducted EMI. 20 volt spikes everywhere on the top floor. >>>>>> Mag fields drop rapidly with distance, 3rd power or something.



    Put the two inductors close together. They will see mostly the same >>>>>>>> mag fields, so a couple of resistors added somewhere will cancel the >>>>>>>> pickup.

    Or add a third, between them, to drive their bottom ends, again >>>>>>>> canceling mag field pickup.

    Or make each L from a pair, arranged so the pickups cancel.

    Or just do three lines of algebra to pick the right resistor value, AC >>>>>>> couple, and be done.


    TV remotes work if you bounce the light off the ceiling in a well-lit >>>>>>>> room.

    "Well-lit", as in probably 1000 lumens of LED or fluorescent light, >>>>>>> which has very little output in the >700 nm region.

    But the acoustic approach would be better. Omni MEMS microphones have >>>>>>>> built-in amps and cost 20 cents.

    There are lots of imponderables there, though. For instance, on account
    of the slow speed of sound in air, a 1 m/s breeze (2.2 mph) will make >>>>>>> the apparent direction of the acoustic source move by 3 mrad.

    It's homing into the mother ship so a breeze will very slightly curve >>>>>> the path.

    You're an optics guy, so maybe don't like the sound thing.


    Hidebound prejudice is the only possible explanation. ;)

    Cheers

    Phil Hobbs

    (I don’t necessarily dislike the sound idea, but it’s more of a science >>>>> project than the LED approach. )

    Think so? A quick experiment would be easy. Two MEMS mikes would feed
    an oscilloscope directly. No inductors or TIAs or filters needed. One
    could trigger the scope from the source and signal average for extra
    fun.

    The phase difference between two microphones would be a great
    direction sensor. This would be so easy in production, a couple of
    surface-mout MEMS mikes on a PC board.

    The advantage of the photo diode solution, is that it's all analog, so
    can be build and tested quickly, without ordering a PCB

    You can solder some wires onto a MEMS microphone.

    Optical: imagine that the docking station has a small vertical wall
    inside a cavity or equivalent. There's an LED set back on each side,
    so the robot sees one LED or the other as it moves side to side. The
    robot has a single photodiode staring ahead.

    Drive the two LEDs at different frequencies. Too far left, you will
    hear BEEP. Too far right, hear BOOP. Sort of like the old airplane
    landing thing.

    Looks promising with two LEDs and a business card.

    Yes, that's how the Luba does it:

    https://youtu.be/tKSR9LqHPDI?si=0V9nWtexG4yKP_wO&t=110

    I have shifted to that too, then only a single receiver is needed.

    On the topic of optics, some LIDAR system uses 940nm, since water
    absorption removes most of the sunlight interference:

    https://www.e-motec.net/wp-content/uploads/2022/02/10.png

    But, for this IR system, the power output is close to a million times
    lower than a LIDAR, and water absorbtion could reduce the beam strength
    from emitter to receiver if there's fog or rain.

    Would 940nm be a good choice for a IR system?




    The credit card experiment is morally equivalent to using two square
    tubes stuck together. Now mount two LEDS, red and green, to the common
    wall, at the back of the tubes. Shine that at a wall. It should
    project two fuzzy squares, red and green, barely overlapping, with a
    fuzzy orange stripe between them.

    That could actually be two IR LEDs modulated at different frequencies,
    or two photodiodes.

    TV remotes work very well, so I wouldn't expect s/n problems with the
    emitter and detector staring at one another a few feet apart.

    Use multiple LEDs stacked vertically along both sides of that back
    wall (which should actually be a PCB) and apply a lot of square-wave
    current.

    We like the Osram right-angle surface-mount LEDs, but there are lots
    of parts like that around.

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  • From Bill Sloman@21:1/5 to john larkin on Thu Oct 31 14:17:57 2024
    On 31/10/2024 2:09 am, john larkin wrote:
    On Wed, 30 Oct 2024 09:45:42 +0100, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    On 30-10-2024 00:31, john larkin wrote:
    On Wed, 30 Oct 2024 00:02:34 +0100, Klaus Vestergaard Kragelund
    <klauskvik@hotmail.com> wrote:

    On 29-10-2024 18:26, john larkin wrote:
    On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <jl@glen--canyon.com> wrote:
    On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 17:10, john larkin wrote:
    On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>>>> <klauskvik@hotmail.com> wrote:

    <snip>

    The credit card experiment is morally equivalent to using two square
    tubes stuck together.

    He meant conceptually equivalent. Components don't have morals.

    Now mount two LEDS, red and green, to the common
    wall, at the back of the tubes. Shine that at a wall. It should
    project two fuzzy squares, red and green, barely overlapping, with a
    fuzzy orange stripe between them.

    It will look orange to a human being because our optical frequency discrimination system sucks.

    That could actually be two IR LEDs modulated at different frequencies,
    or two photodiodes.

    TV remotes work very well, so I wouldn't expect s/n problems with the
    emitter and detector staring at one another a few feet apart.

    TV remotes are doing a rather different job.

    Use multiple LEDs stacked vertically along both sides of that back
    wall (which should actually be a PCB) and apply a lot of square-wave
    current.

    Why square wave? It's just the sum of the sine wave fundamental, and all
    the odd harmonics of that fundamental. A triangular wave is just as easy
    to generate, and while it has the same harmonics,the amplitudes drop off
    as the square of the frequency. Generating a sine wave isn't all that difficult.

    We like the Osram right-angle surface-mount LEDs, but there are lots
    of parts like that around.

    Scarcely the right part for this particular job.

    --
    Bill Sloman, Sydney

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  • From Jasen Betts@21:1/5 to Klaus Vestergaard Kragelund on Sat Nov 2 00:03:55 2024
    On 2024-10-27, Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:

    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    Perhaps amplitude modulate the signal and look at pulse-width in the
    receiver? Or maybe you can modulate the receiver supply voltage to mess with the
    sensitivity? Or look for a side channel to read the AGC setting, perhaps supply current?
    Or have the robot yaw to do a physical search to find the edges of the digital signal.


    If you do decide to go analogue, maybe you can run at 32.768kHz and
    use a crystal in the filter?

    --
    Jasen.
    🇺🇦 Слава Україні

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  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Mon Nov 4 09:53:55 2024
    On Tue, 29 Oct 2024 16:03:12 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <JL@gct.com> wrote:
    On Mon, 28 Oct 2024 20:19:25 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 08:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low >>>>>>>>>> duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam >>>>>>>>>> that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/ >>>>>>>>>> Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not >>>>>>>>>> just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I >>>>>>>>>> would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering. >>>>>>>>>

    That's a very nice idea. The Q should not matter much, just as long as >>>>>>>> DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>
    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single >>>>>> transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor.

    But the dual microphone thing, electret or mems, sounds like a much
    better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli
    henries.

    Of course they might be able to reverse the process and have one receiver >>>> on the robot and two emitters on the docking station, a bit like aircraft >>>> VOR

    Or like certain radio navigation systems popular in Western Europe, 80
    or so years ago. ;)

    That's a good example of Horace Darwin's maxim, "Always try it the other >>> way round", quoted in "Instruments and Experiences" by R. V. Jones.

    Jones is one of my technical heroes, and was instrumental in defeating a >>> couple of the aforementioned navigation systems, specifically
    "Knickebein" and "X-Geraet", as explained in his book, "The Wizard War"
    (entitled "Most Secret War" in the UK). Horace Darwin was a grandson of >>> Charles Darwin, and a colleague of Jones's at Aberdeen after the war.

    Cheers

    Phil Hobbs

    https://www.amazon.com/Instruments-Experiences-Measurement-Instrument-Technology/dp/047191763X




    Cheap at twice the price!

    It’s a unique book—a collection of Jones’s groundbreaking papers on things >like measuring the ether drag on light in a moving dielectric, which would
    be a niche interest except that each one is paired with an essay of about >equal length explaining how the measurement was done.

    Those pieces are of lasting value—they’re confidential in tone, including
    the inventions required, the blind alleys, and very often, how somebody
    made a big difference with a piece of hard-won advice, like that remark of >Darwin’s.

    Cheers

    Phil Hobbs

    One of my summer jobs in high school was working in the electronics
    shop of the physics depertment of a local university. They registered
    me as a fake student so they could pay me 70 cents per hour. I learned
    a lot.

    I designed some stuff for Mössbauer spectroscopy, which is astounding
    physics. Gamma-ray absorption lines turn out to be pretty high Q.

    https://en.wikipedia.org/wiki/M%C3%B6ssbauer_spectroscopy

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Mon Nov 4 18:57:55 2024
    john larkin <jl@glen--canyon.com> wrote:
    On Tue, 29 Oct 2024 16:03:12 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

    john larkin <JL@gct.com> wrote:
    On Mon, 28 Oct 2024 20:19:25 -0400, Phil Hobbs
    <pcdhSpamMeSenseless@electrooptical.net> wrote:

    On 2024-10-28 08:14, piglet wrote:
    john larkin <JL@gct.com> wrote:
    On Sun, 27 Oct 2024 22:59:59 -0000 (UTC), piglet
    <erichpwagner@hotmail.com> wrote:

    Klaus Vestergaard Kragelund <klauskvik@hotmail.com> wrote:
    On 27-10-2024 13:26, Klaus Vestergaard Kragelund wrote:
    On 27-10-2024 03:26, john larkin wrote:
    On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund >>>>>>>>>> <klauskvik@hotmail.com> wrote:

    Hi

    I am working on an IR detector that will guide a robot into a docking
    station.

    A IR transmitter on the docking station transmits a beam, and 2 IR >>>>>>>>>>> detectors on the robot detects the beam and lets the robot navigate >>>>>>>>>>> towards the target. The working distance is a couple of meters. >>>>>>>>>>>
    I need it to be insensitive to ambient light/sunlight.

    The IR detectors are placed in a tube, to narrow in the beam angle and
    to avoid sunlight (since it is seldom the sun is actually that low in
    the horizon)

    The IR transmitter will be modulated with 10kHz (TBD) frequency, low
    duty cycle. Low duty cycle to be able to drive the LED with high >>>>>>>>>>> current, frequency modulated so that the receiver can ignore the effect
    of daylight (DC)

    If the LED on the docking station has higher radiant intensity at the
    point of the robot (2 meters away) than possible IR from sunlight, then
    that would be perfect.

    Example of transmitter:

    https://www.vishay.com/docs/83398/vsmy2850.pdf

    Has up to 1000mW/sr. Seems my basic calculation for a 15 degree beam,
    shows less than 10nW/m2, while sunlight has 1W/m2. So driving a beam
    that has higher output than sunlight seems unlikely.

    I would use a IR phototransistor at 850nm, something like this: >>>>>>>>>>>
    https://www.ttelectronics.com/TTElectronics/media/ProductFiles/ >>>>>>>>>>> Datasheet/OP505-506-535-705.pdf

    Or a photo diode:

    https://docs.rs-online.com/9f58/0900766b816d8a09.pdf

    Fed from reverse 3.3V and into a transimpedance amplifier to boost the
    signal with bandpass filter.

    One can get digital IR detector used in a remote control systems: >>>>>>>>>>>
    https://www.vishay.com/docs/82491/tsop382.pdf

    It has AGC, but digital output. I need analog output to be able to zero
    in on the transmitter beam.

    I have been looking for IR detectors that has the analog output, not
    just the digital, but have not found any.

    If the photodiode detector is subjected to sunlight, I am guessing I
    would need very high gain on the 10kHz modulation frequency to pick up
    the burried signal in the DC from sunlight.

    How do I best bias the photo diode for optimum detection of the 10kHz
    signal while being immune to the ambient sunlight?

    I have chosen 850nm which seems to be a good wavelength. The spectrum at
    sea level has some dips due to water absorption.

    https://sciencetech-inc.com/web/image/49169/
    Spectrum%20with_out%20absorption.png

    Seems like 750nm would be better, since then the IR from the sun is >>>>>>>>>>> lower, but does reduced the effective range of the system during >>>>>>>>>>> fog/rain. Probably that's why these system do not use 750nm >>>>>>>>>>>
    Other considerations?

    You could drive the LED with a square wave, 10 KHz or whatever. The >>>>>>>>>> photodiode could have +DC on one end and the other end can hit a >>>>>>>>>> parallel LC to ground, resonant at 10K.

    That takes out the sunlight DC component and adds bandpass filtering.


    That's a very nice idea. The Q should not matter much, just as long as
    DC is removed.

    The photodiode will still be subjected to the high ambient light, but >>>>>>>>> the gain would be close to zero for the stage after. I would then still
    need to be sure the photodiode is never saturated by ambient light. >>>>>>>>>
    Actually, wont a simple high pass filter work equally well?

    Photo diode with bias -> capacitor to gain block....


    If you make it part of the bias network yes, a gyrator either a single >>>>>>> transistor or op amp could take the role of inductor.

    When you need an inductor, an inductor makes an excellent inductor. >>>>>>
    But the dual microphone thing, electret or mems, sounds like a much >>>>>> better way to go.



    Some folk are scared of inductors. 10kHz does mean quite a few milli >>>>> henries.

    Of course they might be able to reverse the process and have one receiver >>>>> on the robot and two emitters on the docking station, a bit like aircraft >>>>> VOR

    Or like certain radio navigation systems popular in Western Europe, 80 >>>> or so years ago. ;)

    That's a good example of Horace Darwin's maxim, "Always try it the other >>>> way round", quoted in "Instruments and Experiences" by R. V. Jones.

    Jones is one of my technical heroes, and was instrumental in defeating a >>>> couple of the aforementioned navigation systems, specifically
    "Knickebein" and "X-Geraet", as explained in his book, "The Wizard War" >>>> (entitled "Most Secret War" in the UK). Horace Darwin was a grandson of >>>> Charles Darwin, and a colleague of Jones's at Aberdeen after the war.

    Cheers

    Phil Hobbs

    https://www.amazon.com/Instruments-Experiences-Measurement-Instrument-Technology/dp/047191763X




    Cheap at twice the price!

    It’s a unique book—a collection of Jones’s groundbreaking papers on things
    like measuring the ether drag on light in a moving dielectric, which would >> be a niche interest except that each one is paired with an essay of about
    equal length explaining how the measurement was done.

    Those pieces are of lasting value—they’re confidential in tone, including >> the inventions required, the blind alleys, and very often, how somebody
    made a big difference with a piece of hard-won advice, like that remark of >> DarwinÂ’s.

    Cheers

    Phil Hobbs

    One of my summer jobs in high school was working in the electronics
    shop of the physics depertment of a local university. They registered
    me as a fake student so they could pay me 70 cents per hour. I learned
    a lot.

    I designed some stuff for Mössbauer spectroscopy, which is astounding physics. Gamma-ray absorption lines turn out to be pretty high Q.

    https://en.wikipedia.org/wiki/M%C3%B6ssbauer_spectroscopy





    Yeah, Mössbauer was the basis of the GR time dilation (redshift)
    measurement at the Harvard clock tower (Pound & Rebka, 1960).

    Fun stuff.

    Cheers

    Phil Hobbs
    --
    Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics

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