POT jitter on ADC???

[Harry Bissell]

Yessir. One thing is to decouple the ends of the pot with a bypass cap. This did
the trick on my Prophet V (RIP) six months before the factory found out what was
going on.

2) How big of a cap ??? You should be able to attach it right to the wiper if you
like... the supply will ramp up at whatever speed and the cap should follow without
complaint without worry about wiper position (this aint 1000uF now is it ???) The
Pot would form a RC filter but the time constant would vary a little.

3) How fast can the supply ramp down... this is the problem. The diodes up and down
would protect the ADC here, the voltage can never go more than one drop above
whatever the rail is... a series resistor to the ADC might be extra insurance.
Shottky diodes have even lower forward voltage 1N5817 is about .35-.40 volts.

Most times the ramp issue is for big caps with power supplies that can fall
suddenly, like those with Crowbar circuits, or subject to short circuits (drop a
screwdriver in it...) I think
you are pretty safe here...

H^) Harry

Batz Goodfortune wrote:

> Y-ellow y'all.
>         The question: If I stuck a suitably sized cap across the wiper of a POT
> and ground, which feeds the input to an A-D converter, would it...
> (a) Stop the occasional jitter from the pot?
> (b) Cause damage to the input of the A-D on power up/down?
>
> The problem: I have an A-D converter reading a POT. That's all it has to
> do. It works OK but occasionally the pot positions it self where it
> jitters. Like it's a switch bouncing. It reeks havoc sometimes. Especially
> on bootup. I was thinking that maybe a cap on the input of the A-D with a
> small series resistor from the wiper of the pot might do the trick. But
> then I thought that the charge on the cap might fry the input as the
> voltage falls on power down. Taking the input beyond it's safe operating area.
>
> I thought that maybe if I also placed a pair of diodes across the input,
> Cathodes pointing up to Vcc might protect it?
>
> Anyone have experience with this kind of thing?
>
> Thanks in advance.
>
> be absolutely Icebox.
>
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