Record potentiometer levels from a live device?

Not sure how to word the title of this correctly but I am trying to accomplish is a way to record where the potentiometers have been set on a device that is currently 'working'. I dont want to disrupt the job the pots are currently performing, just grab their values while they are doing it. Is this something that is possible to do?

It depends on what job they're doing. If they're passing DC voltage, no problem. Just measure it. If they're passing AC voltage or a signal, it will be harder.

Mark it with a pen? Take a picture? (That won't be precise so it may be no-good if the settings are critical or if the adjustments are "touchy".)

In some circuits you can measure the resistance with your multimeter (with the power off) but in other cases the connected-circuitry may affect the readings.

...If these are calibration pots or something like that (or something you don't know) you shouldn't touch them unless you have the calibration procedure.

To clarify, these pots are from a small synthesizer that I want to record the values into the arduino. In this case they would be passing a signal I am guessing.

Which "small synth"? Do we have to guess?

If it is newer than 1984 then it probably isn't passing signals through the pots.

Volca Sample. I have done numerous other mods successfully on the volca line just had an idea if I could grab the potentiometer positions.

Just measure the voltages across the pot, if they are 5V or 3.3V across the outermost pins, they are digital, and you should be able to read them with an analog input.

Pieter

If they do pass a signal, maybe you can change the potentiometer for a stereo pot if there is enough room!

PieterP: Just measure the voltages across the pot, if they are 5V or 3.3V across the outermost pins, they are digital, and you should be able to read them with an analog input.

Pieter

This is exactly what I was trying to confirm! If they do end up being digital, could i simply solder a wire to the center pin and bring it to an analog input on the Arduino to read its level?

Allordacia1: This is exactly what I was trying to confirm! If they do end up being digital, could i simply solder a wire to the center pin and bring it to an analog input on the Arduino to read its level?

I think PieterP meant to say DC not digital?

Anyway, if they are DC and not AC (a signal) then yes you could just measure the voltage across the pot. Remember to have common ground between the circuits though or you will not be able to measure anything useful.

You should probably measure the voltage over the potentiometer, with both AC and DC settings! Any AC voltage could have a DC offset, so only measuring DC voltage doesn't guarantee you anything. It could for example be something like a +/- 100mV AC signal with a 2.5V DC offset. Do you have an oscilloscope?

GeronimoDK: I think PieterP meant to say DC not digital?

I meant that the device uses an ADC to read the value of the pot, and that it is not used for analog signals.

GeronimoDK: I think PieterP meant to say DC not digital?

Anyway, if they are DC and not AC (a signal) then yes you could just measure the voltage across the pot. Remember to have common ground between the circuits though or you will not be able to measure anything useful.

You should probably measure the voltage over the potentiometer, with both AC and DC settings! Any AC voltage could have a DC offset, so only measuring DC voltage doesn't guarantee you anything. It could for example be something like a +/- 100mV AC signal with a 2.5V DC offset. Do you have an oscilloscope?

So I checked both while the device was on and while it was off. AC is getting a small current, less than a Volt. Checking DC would shut the machine off while it was off when i touched the outer pins but while it is off it measures 0 volts on the outside pins. Middle pin and negative pin measure ohms fine while the device is on if that means anything in this.

If the device shuts off, you're doing something terribly wrong. Only measure voltages, not resistance.

PieterP: If the device shuts off, you're doing something terribly wrong. Only measure voltages, not resistance.

Crap! Good call I had my multimeter set to DC mA and not DC voltage... checking again

DC Voltage reads 3.3! So If I go from center pin to arduino analog input and arduino ground to a ground point on the PCB I will be able to record the positions of the pots? Other thought, Any way I can send a digital value back?

Allordacia1:
DC Voltage reads 3.3! So If I go from center pin to arduino analog input and arduino ground to a ground point on the PCB I will be able to record the positions of the pots?

Yes. Just don’t ever use the Arduino pin as output.

Allordacia1:
Other thought, Any way I can send a digital value back?

Not without ripping out the potentiometers entirely and replacing them with a digital potentiometer.

Or use a motorized pot. That would require major surgery on the panel as motorized pots are usually large.

A stereo motorized pot can use the second track as a position sensor while AC or DC signal passes through the first. But it seems like you don't need that expense for this application.

PieterP: Yes. Just don't ever use the Arduino pin as output. Not without ripping out the potentiometers entirely and replacing them with a digital potentiometer.

Not out of the question, the solder joints on the PCB are a very decent size and Im doing the surgery on this one as a proof of concept so i am willing to take a little risk with it... Ill check reading the values first and then go from there. Thanks!