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From: Jan Panteltje <alien@comet.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Upper limit of timing resistor value in a tropical setting
Date: Fri, 20 Sep 2024 10:15:18 GMT
Message-ID: <vcjhvn$g5g3$1@solani.org>
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On a sunny day (Fri, 20 Sep 2024 14:18:26 +0530) it happened Pimpom
<Pimpom@invalid.invalid> wrote in <vFaHO.92333$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...