• IR detector again

    From Hul Tytus@21:1/5 to All on Mon Nov 11 16:31:56 2024
    Klaus, you might mount the tubes at a slight outward angle. When one is saturated steer toward the other.
    R V Jones' "Most Secret War", which Phil mentioned, describes a German navigational aide that quided aircraft on landing. Two beams were lined
    up with the runway but diverging a few degrees. The pilot approached
    keeping the reception of the beams equal.
    Your approach has a higher frequency with reciever/transmiter
    altered some. All in all though, suprisingly similar.

    Hul


    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:
    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:
    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:
    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?

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  • From Wanderer@21:1/5 to All on Mon Nov 11 04:48:33 2024
    On Mon, 11 Nov 2024, Hul Tytus wrote.

    Klaus, you might mount the tubes at a slight outward angle. >When one is
    saturated steer toward the other.
    R V Jones' "Most Secret War", which Phil mentioned, describes >a German
    navigational aide that quided aircraft on landing. Two beams were >lined
    up with the runway but diverging a few degrees. The pilot >approached
    keeping the reception of the beams equal.
    Your approach has a higher frequency with reciever/transmiter
    altered some. All in all though, suprisingly similar.

    Hul

    It's the fly's ear problem. The fly's ear does this mechanically. You take
    the sum and the difference of two signals. If the sum is high enough you
    have signal. Then the difference tells you the direction. You try to zero
    the difference while maintaining the sum to fly straight at the signal.

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  • From Joe Gwinn@21:1/5 to Wanderer on Mon Nov 11 17:25:05 2024
    On Mon, 11 Nov 2024 04:48:33, Wanderer<dont@emailme.com> wrote:

    On Mon, 11 Nov 2024, Hul Tytus wrote.

    Klaus, you might mount the tubes at a slight outward angle. >When one is >>saturated steer toward the other.
    R V Jones' "Most Secret War", which Phil mentioned, describes >a German >>navigational aide that quided aircraft on landing. Two beams were >lined
    up with the runway but diverging a few degrees. The pilot >approached >>keeping the reception of the beams equal.
    Your approach has a higher frequency with reciever/transmiter
    altered some. All in all though, suprisingly similar.

    Hul

    It's the fly's ear problem. The fly's ear does this mechanically. You take >the sum and the difference of two signals. If the sum is high enough you
    have signal. Then the difference tells you the direction. You try to zero
    the difference while maintaining the sum to fly straight at the signal.

    In radar, this is called Monopulse.

    .<https://en.wikipedia.org/wiki/Monopulse_radar>

    Joe Gwinn

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