Multiple pots switching with a mux

So I build this tig pulser and it seems to be working fine when testing it with a scope but I can’t get my head around the workings of two of the pots. They are simple enough, one is connected to + and - and the wiper goes out to an input on a mux and also to the other pot which makes the second pot a percentage of the first.
A picture says more :laughing:

Here they are named TIG Pedal and Background Current.
I am switching the inputs on the mix with Arduino code and it actually works. The second pot gives a percentage of the first, from (roughly) zero to a hundred percent.
But when I do a little test in EveryCircuit I get completely different results since it sees the pots as serial connected ones (I guess).

I’d like to better understand what is actually happening and maybe I am looking at it the wrong way?

Do you have a real schematic available too?

I will come up with a proper schematic as well. Is the one from EveryCircuit ok?

May be handdrawn.

The schematic is correct, perhaps your understanding is wrong?
The "Background Current" 5k pot is loading the "TIG Pedal" pot.
Change the "Background Current" pot in EveryCircuit to a big value - say 1M so it wont significantly change the value from the tig pot.

A 1Meg pot near a welder is basically a noise antenna - I suspect the TIG pedal pot is quite low in value for the same reason. I'd use a much lower value like 20k for background current to reduce noise sensitivity

All those analog inputs need capacitors to short out any noise pick up from the wleder, welders put out copious noise and you need to be fanatical about shielding and screening and so forth.

I got a bit further when I made a schematic and saw what I did wrong.

However, I now discovered another issue. I have 9V coming in that I need to lower below 5V for my mux to be able to handle it. With one resistor and one pot it is straight forward as you can see in the schematic with the contact closed. But when I open it I have two pot and the resistor and then I don’t get the 4,5V to the second pot. Any ideas of how I would go about instead would be greatly appreciated :slight_smile:

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.