Josh Koffman wrote:

>  When I built them, they were solid, meaning that if I
> didn't move the slider, the value stayed consistent.

Were all the unit external inputs and outputs connected and operating at=20
full currents and cable lengths?

>=20
> A few months ago I saw a few of them still in action, and the values
> were...fluttering a bit. So even if the slider was not being moved,
> the value transmitted fluctuated a bit around where it should be (say
> by about 1-2% in each direction).=20

Assuming 5v supply and 8 bits (255 count) then 1 bit is about 20mv.
If your 1 to 2% is a percentage of the FSD of 5 volts that is 50 to=20
100mV i.e about 2 to 5 bits. I would hope for +-1 bit.

>=20
> I originally had this set up as a simple voltage divider with a series
> resistor to protect the input pin if the slider was at one extreme or
> the other and the pin was accidentally set to output.

I think you have to consider the total resistance seen by the ADC input=20
is not too high when the pot is in the middle - i.e. keep the series=20
resistor as low as possible and the pot resistance as low as current=20
consumption/heating will allow.

PCB layout especially ground tracking is important.

I would work on a suspect unit and turn the pot to minimum (0v rail) -=20
any noise then should not be due to the power supply but could be series=20
mode noise - probably due to digital circuit currents in the ground=20
track between the ADC 0v pin and the pot low end.
Obviously if the noise increases as you turn the pot to the 5 volt end=20
then the supply rail is likely to be the source - again probably due to=20
digital spikes.

George Smith

--=20
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