I have strange problem with 3590s 10 turns precision potentiometer. Sometimes pot readings jump during operation. When I checked resistance using multimeter (after disconnecting it from circuit), got following observations.
VCC to Wiper pins : resistance varies
VCC to GND pins : resistance varies
GND to Wiper pins : resistance stable.
My understanding was that wiper in issue can make resistance jump, since that's the moving part. But above observations says something wrong with VCC pin, but my understanding is that it's stationary pin so nothing should probably go wrong with it. Is my understanding correct?
And, if there is something really wrong with VCC pin of pot, can I bypass it altogether using a external resistor as shown in following diagram? Maybe I will not get full 0-1024 signal range on analog pin, but as long as I get signal stability, I can work with it.
You seem to confuse the pins. The stable resistance applies to the entire pot, the remaining pin is the wiper. The wiper is not necessarily the middle pin with these pots.
Resistance jumps can occur with wire wound pots, when the wiper jumps from one wire turn to the next one..
I'm assuming when you say "varies" you mean the OhmMeter reading changes when the Vcc is in the measurement but the wiper is not being used.
It appears the pot connection 1 or 3 has a loose connection. I don't know of a method to remedy this. If Vcc had been connected to the wiper at one time and the pot turned to the end an over current may have damaged the pot.
My only suggestion is to use the pot with the Gnd and wiper only, add a resistor between the wiper and Vcc. This will be very nonlinear but you can linearize it in code.
Thanks everyone for your inputs!!
Finally dismantled pot and found it to be damaged from inside, hence causing jumping resistance between vcc and gnd. During operations it was pressed too much on one side damaging it's internals.
As @JohnRob suggested, planning to add external resistor and use in non-linear way.
