# Reading pot from other circuit

Fault currents will find their way through the signal wires once ground differential is more than a few volts, blowing up the muxer and/or the Arduino.
Leo..

Not only do the same electrons not stick to the same circuit, they do not even move that fast on average! They just sort of wander from one atom to the next, kicking the next one along as they go. The actual speed is tiny!

I never thought much about the speed of electron flow (at least not since college). But I believe an ampere is:

Current is a measure of the rate of electron flow through a material. Electrical current is measured in units of amperes or "amps" for short. This flow of electrical current develops when electrons are forced from one atom to another. One amp is defined as 6.28 x 10^18 electrons per second .

There is however "Drift Velocity" resulting from an EM wave. Drift Velocity is tiny, in the order of 1 mm /second.

I only researched this because I though electrons moved pretty quickly, but its been a long time. I didn't ever remember "Drift Velocity"

I’m getting the hang of it and I got it to work in the test setup
One thing I noticed when I was about to hook it up to the welder is that the input that I thought was 3,3V was actually 9V. That’s manageable but the 9V does not get turned on until the welding has started. Is it somehow possible to read the potentiometers setting without a voltage applied to it? I know this is kind of a stupid question but what I really want to do is just to display the setting in percent, from 0-100 basically.

Yes and no.

You could run a low current through the welder pot and read its value. This would assume (a pretty safe assumption) that when the 9v is energized it will overcome the low value current you were adding.

For instance, from 5V, connect a 10k in series with the welder control.

I considered suggesting a relay between the welder pot and the welder that would be closed as soon as the 9V appears, however I fear this may be sensed by the welder as a fault.

Thanks, that’s interesting suggestions