Help interpreting a schematic (building a TIG foot pedal from scratch)

[Marc Dehoux]

Hello!

I want to build a foot pedal for my TIG welder. I am fairly capable with wiring and soldering, and I can do ok reading schematics when needed. The schematic provided by Miller in their manual though, doesn't show or reference any values for the components.

I'm wondering how I can best determine the value, in the absence of a working pedal.

I have attached the schematic they provide.

Through google searching, it looks like the potentiometer used is a 1k, 2 watt. I am not sure how to determine the values to use on the decoupling capacitors for C1 and C2.

Thanks for any help!

[Tony Brenke]

You can use .1uf caps for that. They are just used to take the noise ripples out that the pot makes

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[Kel]

The caps are for noise reduction, but the pot is what is important.  This conversation may help you out.....
http://weldingweb.com/showthread.php?7304-Difference-in-pedals

[Marc Dehoux]

Outstanding! Would a certain capacitor be better than another for this type of application? Ceramic vs film vs etc?

[Tony Brenke]

for switches (5V low current) and trim pots the ceramic version is fine.  your not doing anything exotic with this.

a tantalum cap will have a lower impedance but your rate of change and the ripple produced by this will be small anyway. wasted money for a tantalum.

[Mike Bushroe]

Mark, that is the exact same circuit diagram I saw Nate using to work on the Lab's TIG foot pedal. I seem to remember the DVM showing 10K on the pot at max, but it might also have been 5 K. You also need to be careful on which wire goes to the side of the pot that will be highest resistance when the foot pedal is up. I vaguely remember that it went on the reverse of what I expected, with highest resistance when the pedal is up going to brown (which looks from the wiring to be ground). But I could be wrong as it has been some time. I could not open the tread in the welding web forum, so I don't know if they answered all these points already.

I agree with the above that it appeared to all be low voltage stuff in the pedal. But I would still consider a bypass type cap for the circuit as the TIG probably induces a lot of EMF near it produce the constant current - variable voltage needed for adjusting the welding arc. But a ceramic 0.1 to 1.0 used to bypass digital chips on a circuit board provide the same function and should work well and are plentiful and cheap.

Mike