# How to use Lynxmotion FSR-01 Force Sensing Resistor Kit to make a variable amperage controller

I’d like to make a remote amperage controller for my welder and wanted to get some more information on my options to go from the Lynxmotion fsr kit to an 8 pin male aviation plug. The board in my welder only uses 5 wires Configured like in the pic

The force sensing resistor is effectively as its name indicates - it’s a resistor whose resistance changes based on the force being applied to the pad. It seems like pins 5,6,7 are for a variable input from the foot switch (check out the pinout of a potentiometer to get an idea). Unfortunately it does not indicate the voltage being applied. As such, cannot give an exact way to connect, but can give you a bit of terms to look up to guide you in the right direction:

• Potentiometer
• Voltage divider

Take note of:

• Voltage input
• Connector length

Thanks for the reply, yes pins 4,5, and 6 are the variable Input and pins 2, and 3 are the signal wires that connect to a mini limit switch. As for voltage the welder produces 12v-26v but the signal voltage is 5v.

What I aim to accomplish is to use the fsr in combination with a Arduino mini pro board, want to use the fsr under the trigger switch so that the more I push the trigger down the more amperage the welder puts out.

If the signal is 0-5V, and you’re effectively replacing a 0-5V potentiometer, there’s a chance you might be able to use a single voltage divider circuit to do that - without the need for a microcontroller.

There are several FSRs here (the Lynxmotion one might be a bit small for human input):

Be sure to do the calculation to find the right equivalent resistance.

Thats what I needed help with, I’ve seen and tinkered with pleantly of foot pedal wiring and stuff but I haven’t done alot when it comes to using boards and the components evolved, I’ve wired up guitars with dual pick up’s but that’s just a matter of connecting the pots in different arrangements and connecting the pickups to the output jack and pots.

I need a fsr that’s small like a video game controller button, the end goal is to fit everything inside of a shell like the trigger switch in the pictures.

I will send a picture of the innards of a rotary style amperage controller this will give an idea of what I hope to achieve using the fsr instead of the rotary system.

The circuit looks relatively simple, with one potentiometer and two capacitors (perhaps to smooth out the signal). Ideally, you’d verify each pin with a multimeter (set to voltage) and rotate the potentiometer to verify the voltage output. Ideally you’ll find that one is GND, the other remains 5V and the third varies from 0V to 5V as you rotate the pot. If so, you can create a simple voltage divider circuit using the FSR.

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Ok so in the diagram it showes brown, blue, and red wires designated to the potentiometer and the black and white wires are designated to the limit switch. What I am seeing is that the white wire appears to be the power (Common terminal ) and the black wire is power (N/O terminal) and energizes the brown wire (signal/wiper terminal) on the potentiometer, the blue and red wires are min and max resistance.

If I were to use the fsr with the Arduino board like I planned would I just need to solder in a 5 pin header and something to connect the fsr and that’s it? The fsr replaces the potentiometer correct?

Not sure what purpose the Arduino board would serve in that case given the simplicity of the circuit.

A voltage divider circuit would replace the three-pin potentiometer, and the FSR would act as one of the two resistors in the circuit.

Sorry I meant to say if I used the fsr with one of the dividers INSTEAD of the Arduino mini.

oooh ok I was thinking that the fsr replaced the potentiometer being that it essentially does the same thing. So I would wire it with the brown blue and red wires to the signal, ground, and N/C terminals and connect the fsr and the white and black wires to the ground and vcc correct?

I hadn’t taken a close look at the voltage dividers and I assumed it would be set up similar to the board like the one in the pictures I sent recently.

Gotcha - no Arduino.

A basic voltage divider doesn’t include the two blue boxes (marked as C1 and C2, so possibly capacitors). You might want to use a multimeter to probe those, or see if you can find text printed on them to see what they are. Likely to smoothen the signal (a good thing).

As for wiring, it’s important that you know what a voltage divider circuit is and how to calculate the value for the second resistor. You can then compare it to how a rotary pot works to know which connections go where.

Oh that board with the 2 capacitors isn’t involved in this other then a depiction of the size of board I want to end up with. Sorry I should have clarified that. The first pictures of the wiring diagram and the connector plug (8 pin) that’s the circuit I need to match with. And that’s for the foot pedal.

The cable from the foot petal which is the cable I’ll be using to make this fsr switch with, on the potentiometer the red wire is on the first (left terminal ) which is max resistance the brown wire on on the second (middle terminal ) which is Signal and the blue wire is on the third (right terminal ) which is min resistance. There are no capacitors just the micro switch and a 10kohm potentiometer

One last question, what kind of connector will I need to plug into the voltage divider? Is it a female 3 pin jst?

Given the two products above? The first is a standard 0.1" spaced connector, while the second includes an adapter cable which also terminates in a 3-pin 0.1" spaced connector.

I ordered the gravity voltage divider from the options you had linked earlier. Also ordered a jst jumper, didn’t know it came with