TIG Welder Variable Amperage Torch Switch--HELP

Other Miscellaneous
1

Hi,

Looking for a little direction on how to accomplish my first Arduino project. I need help in terms of picking out electronic components and coding.

The project: I would like to make a Variable Amperage Control Switch that mounts to the Torch handle of my TIG Welder. It seems fairly simple but I don’t know much about Arduino or electronics in general. I just started watching TOP TECH BOY’s Arduino Tutorials and I’m curious to see if I’m going in the right direction.

A few details:

In essence I want to make the equivalent of a TIG Welder foot controlled variable amperage switch (looks like a sewing machine foot pedal) that is mounted on the TIG torch handle to be operated by a button that adjusts the amperage the harder you press.

The foot pedal has basically only two components: a 10 Ohm linear potentiometer (3 wires) and a momentary on/off switch (2 wires). I need to mimic this by pressing a button. I think I could accomplish this by using a Force Sensitive Resistor (FSR) #SEN-09375 ROHS and then writing code to correlate finger pressure to a 0 to 10 Ohm range. I think the on/off switch is triggered first to inform the Welder to start the High Frequency control circuit of the welder. So maybe code something that closes the switch loop once the Ohms begin to fall from 10?

I think it would also be helpful to control the sensitivity of finger pressure with maybe a rotating POT? I’m not sure if there is any real current going into the foot pedal for the two switches so I don’t think I will need a relays, but I’m not sure or even how to check the current with a meter through a POT?

As you can probably tell, I don’t know much about electronics, I started looking at the Arduino a few years ago and now I’m trying to pick it up again with this project. Any help our guidance would be greatly appreciated.

P.S. I also attached a pinout of the Foot Pedal for reference.

Thanks,

BTIDADDY

AHP AlphaTIG 2016 Foot Pedal Pinout.pdf (259 KB)

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Hi BTIDADDY.

I’m not sure an Arduino would be good for something like this. An Arduino can’t emulate a potentiometer and the potentiometer in your foot pedal might need to dissipate quite a bit of power in a welding application.

An easier way to look at this might be to build something that can turn the potentiometer you already have in the foot pedal. Possibly by using a servo motor that’s Arduino controlled with by a force sensitive resistor. A relay could be used to emulate the switch in your foot pedal. I’m not sure how well this would work in an electrically noisy environment though.

You’d need to write the code that drives both the relay and servo motor, but those parts inside the pedal could emulate a person stepping on the pedal. This tutorial might be a good starting point. The potentiometer in the circuit could be a force sensitive resistor and the servo motor would rotate your potentiometer.

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Hi TS-Chris,

Thank you very much for your thoughtful and speedy reply! Much appreciated. :slight_smile:

Hummm. I was really hoping I could make the FSR work without a servo. I’ve played with servos in the past and maybe they were cheap servos I’ve used but they didn’t seem very repeatable and as I recall they were kind of “jerky” in their movement. I need a smooth adjustment of amperage for my application–however, I will go that way if I have no other choice. I won’t be modifying the foot pedal. I want to build something new that emulates the foot pedal with all new parts. How can I check the maximum current flowing through the foot pedal potentiometer to properly size the new one? All I know is it’s a 10 Ohm linear Potentiometer. And can you recommend a servo and other components that I might use if I go that route. Also, clicking on the tutorial you referenced in your first response did not go anywhere for me.

I probably don’t know what I’m talking about, but it seems to me that an FSR and a potentiometer accomplish the same thing-- varying the flow of current by adjusting resistance? Therefore, if I could find an FSR that can handle the current for my application or somehow pass those readings to a higher current circuit of the welder then that would be my preferred method. However, I am warming up to the idea of using a servo. I see a commercial product called the TIG BUTTON that appears to use an FSR and a small black project box about the size of what an Arduino UNO would fit in. I don’t know, but it doesn’t seem like a servo is in the box. And, if the servo dies while the POT is rotated FULL ON, that would be bad. I don’t like moving parts for reliability concerns, but maybe I’m wrong?

Thanks,

BTIDADDY

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I was really hoping I could make the FSR work without a servo.

Unfortunately we don’t have any 10 ohm FSRs and the ones we do carry only have 2 terminals. It looks like you need three terminals.

How can I check the maximum current flowing through the foot pedal potentiometer to properly size the new one?

You’d need to connect an ammeter in series with the potentiometer to measure how much current is flowing through it. 10 ohms is an unusually low value for a potentiometer and you generally only see large currents flowing through potentiometers that have a value that low. The FSRs we carry only work with very small currents so I don’t think they would work in your application.

it seems to me that an FSR and a potentiometer accomplish the same thing-- varying the flow of current by adjusting resistance? Therefore, if I could find an FSR that can handle the current for my application or somehow pass those readings to a higher current circuit of the welder then that would be my preferred method. However, I am warming up to the idea of using a servo.

A FSR and potentiometer do a very similar task. A FSR simply changes it’s value where a potentiometer changes the the ratio of resistance between two resistors. (That’s why it has 3 terminals.) It sounds like your welder is expecting to see a three terminal device rather than a 2 terminal one. I don’t know enough about welders to tell you if you could adapt a 2 terminal FSR to work with your specific piece of equipment, but it might be possible by adding another fixed value resistor to one of the FSR terminals.

All I know is it’s a 10 Ohm linear Potentiometer. And can you recommend a servo and other components that I might use if I go that route. Also, clicking on the tutorial you referenced in your first response did not go anywhere for me.

It’s hard to say without knowing how big your pot is. A standard sized hobby servo would probably work but I can’t say for sure.

I see a commercial product called the TIG BUTTON that appears to use an FSR and a small black project box about the size of what an Arduino UNO would fit in. I don’t know, but it doesn’t seem like a servo is in the box. And, if the servo dies while the POT is rotated FULL ON, that would be bad. I don’t like moving parts for reliability concerns, but maybe I’m wrong?

Again, I don’t know how welders work so there could be some sort of digital trickery going on in that box. It’s possible the welder might even have a separate input for something like this that’s not a potentiometer. You’d need to contact the manufacturer of your welder to know for sure.

I wish I were able to help more, but there are too many unknowns for me to be able to give you good advice other than to construct something that emulates your foot physically moving a foot pedal.