• Upper limit of timing resistor value in a tropical setting

    From Pimpom@21:1/5 to All on Fri Sep 20 14:18:26 2024
    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not
    critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

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  • From Liz Tuddenham@21:1/5 to Pimpom on Fri Sep 20 10:21:52 2024
    Pimpom <Pimpom@invalid.invalid> wrote:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    I've experienced damp getting into the laminated structure of a printed
    circuit board and causing tracking in all directions. Under those
    conditions it would be better to ignore all the usual advice and use 10k
    or less and an electrolytic capacitor.

    Remember the capacitors and ICs have exposed terminals which can
    track-across, so the resistor might not be the only limiting factor. In
    really damp circumstances, or with high voltages, I would consider using
    PTFE standoffs with wire-ended components - they should be good up to
    about a Megohm.


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

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  • From Jan Panteltje@21:1/5 to Pimpom@invalid.invalid on Fri Sep 20 10:15:18 2024
    On a sunny day (Fri, 20 Sep 2024 14:18:26 +0530) it happened Pimpom <Pimpom@invalid.invalid> wrote in <vFaHO.92333$lZG8.68980@fx09.ams1>:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not >critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    100 k would be a high limit
    10k 22k better
    But s Microchip PIC with internal clock is slightly temperature sensitive
    but can create any timer, uses almost no power, and can do many more things. Requires some programming though.
    No timing caps and resistors needed...

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  • From Pimpom@21:1/5 to Jan Panteltje on Fri Sep 20 19:13:32 2024
    On 20-09-2024 03:45 pm, Jan Panteltje wrote:
    On a sunny day (Fri, 20 Sep 2024 14:18:26 +0530) it happened Pimpom <Pimpom@invalid.invalid> wrote in <vFaHO.92333$lZG8.68980@fx09.ams1>:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not
    critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    100 k would be a high limit
    10k 22k better
    But s Microchip PIC with internal clock is slightly temperature sensitive
    but can create any timer, uses almost no power, and can do many more things. Requires some programming though.
    No timing caps and resistors needed...


    Yes, I suppose I could use one of the simpler ATTiny MCUs or an Arduino
    Nano. But the whole thing uses a common 12V supply and using an MCU will require a buck regulator and scaling of the input and output.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Pimpom@21:1/5 to Liz Tuddenham on Fri Sep 20 19:12:44 2024
    On 20-09-2024 02:51 pm, Liz Tuddenham wrote:
    Pimpom <Pimpom@invalid.invalid> wrote:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not
    critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    I've experienced damp getting into the laminated structure of a printed circuit board and causing tracking in all directions. Under those conditions it would be better to ignore all the usual advice and use 10k
    or less and an electrolytic capacitor.

    Remember the capacitors and ICs have exposed terminals which can track-across, so the resistor might not be the only limiting factor. In really damp circumstances, or with high voltages, I would consider using
    PTFE standoffs with wire-ended components - they should be good up to
    about a Megohm.


    I made a gadget with a similar purpose back in 2008 and it's still in
    use in a video studio, although this one is of a completely different
    design.

    I used an opamp as a Schmitt trigger as the timer in that earlier one
    with the timing set by a 100k resistor and an electrolytic cap. The
    current one is to be used with CMOS gates.

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  • From john larkin@21:1/5 to All on Fri Sep 20 08:17:07 2024
    On Fri, 20 Sep 2024 14:18:26 +0530, Pimpom <Pimpom@invalid.invalid>
    wrote:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not >critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    Without condensation, literal drops of water on the board, 1 Meg might
    be fine. Some attention to the board layout would help... extra
    clearances on the critical node, maybe two resistors in series, small
    R and giant C, maybe use an RC oscillator and divide down.

    Why not use a uP? An RP2040 is 70 cents in any quantity, and has an
    oscillator on-chip. ADCs and temperature sensing too.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Joe Gwinn@21:1/5 to All on Fri Sep 20 12:32:25 2024
    On Fri, 20 Sep 2024 14:18:26 +0530, Pimpom <Pimpom@invalid.invalid>
    wrote:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not >critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    Maybe 1 Kohm. Others have said 10K and 100K.

    But why not dip the board in hot wax, to seal the surface? One can
    repair the board without removing the wax, and just re-wax when done.

    Back in the dead-bug era (late 1960s), we would put the vectorboard
    with wired and ICs in a shallow tray of molten wax, and let it cool
    and solidify, protecting the circuitry both physically and
    electrically from damp and salty dust. If repairs or upgrades are
    needed, melt wax, pull board out, make changes, return to wax tray.

    Joe Gwinn

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  • From bp@www.zefox.net@21:1/5 to john larkin on Fri Sep 20 16:31:37 2024
    john larkin <JL@gct.com> wrote:

    Why not use a uP? An RP2040 is 70 cents in any quantity, and has an oscillator on-chip. ADCs and temperature sensing too.


    What is the time-keeping mechanism?

    bob prohaska

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  • From Lasse Langwadt@21:1/5 to john larkin on Sat Sep 21 02:07:30 2024
    On 9/20/24 17:17, john larkin wrote:
    On Fri, 20 Sep 2024 14:18:26 +0530, Pimpom <Pimpom@invalid.invalid>
    wrote:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not
    critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    Without condensation, literal drops of water on the board, 1 Meg might
    be fine. Some attention to the board layout would help... extra
    clearances on the critical node, maybe two resistors in series, small
    R and giant C, maybe use an RC oscillator and divide down.

    Why not use a uP? An RP2040 is 70 cents in any quantity, and has an oscillator on-chip. ADCs and temperature sensing too.


    an AVRtiny would do the job for ~30cents, and you can get mcus much
    cheaper than that

    https://cpldcpu.wordpress.com/wp-content/uploads/2019/08/3-cent-mcu-1.png

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to llc@fonz.dk on Sat Sep 21 09:15:36 2024
    On a sunny day (Sat, 21 Sep 2024 02:07:30 +0200) it happened Lasse Langwadt <llc@fonz.dk> wrote in <vcl2o3$19sta$1@dont-email.me>:

    On 9/20/24 17:17, john larkin wrote:
    On Fri, 20 Sep 2024 14:18:26 +0530, Pimpom <Pimpom@invalid.invalid>
    wrote:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not
    critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    Without condensation, literal drops of water on the board, 1 Meg might
    be fine. Some attention to the board layout would help... extra
    clearances on the critical node, maybe two resistors in series, small
    R and giant C, maybe use an RC oscillator and divide down.

    Why not use a uP? An RP2040 is 70 cents in any quantity, and has an
    oscillator on-chip. ADCs and temperature sensing too.


    an AVRtiny would do the job for ~30cents, and you can get mcus much
    cheaper than that

    https://cpldcpu.wordpress.com/wp-content/uploads/2019/08/3-cent-mcu-1.png


    Nice overview thank you
    even a PIC12C509 clone!

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jasen Betts@21:1/5 to Pimpom on Fri Sep 27 08:43:08 2024
    On 2024-09-20, Pimpom <Pimpom@invalid.invalid> wrote:
    On 20-09-2024 03:45 pm, Jan Panteltje wrote:
    On a sunny day (Fri, 20 Sep 2024 14:18:26 +0530) it happened Pimpom
    <Pimpom@invalid.invalid> wrote in <vFaHO.92333$lZG8.68980@fx09.ams1>:

    Take a typical domestic environment in a tropical region, rather humid
    at times. Assembled board is not conformal coated and some dust is
    expected to seep into the box over the years and settle on the PCB. The
    unit is low voltage and low power with just a few watts dissipated when
    on, and left unpowered for days on end.

    An R-C combination is used to set timing of around 1 sec. which is not
    critical (long-term variation of up to 10% is tolerable). If it gets
    very bad, the board can be cleaned but this should not be required as
    regular maintenance.

    Under these circumstances, what's the highest timing resistor value
    you'd feel comfortable with?

    100 k would be a high limit
    10k 22k better
    But s Microchip PIC with internal clock is slightly temperature sensitive
    but can create any timer, uses almost no power, and can do many more things. >> Requires some programming though.
    No timing caps and resistors needed...


    Yes, I suppose I could use one of the simpler ATTiny MCUs or an Arduino
    Nano. But the whole thing uses a common 12V supply and using an MCU will require a buck regulator and scaling of the input and output.

    CD4060 ? (combine oscillator with divider) this is what the automatic
    room perfumers use SFAICT

    --
    Jasen.
    🇺🇦 Слава Україні

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