How to find where is the pwm signal

Hi ! I am working on a DIY project for sim racing. The goal is to pull on an harness while braking. I am using a 350W DC motor, and this driver. I have an Arduino linked to the PC, able to generate a pwm signal proportionnal to the negative G’s.

The problem is that the driver is controlled by a potentiometer, not a pwm signal. I could use na RC circuit, but it doesn’t seem to work. So I disassembled the driver and start to look after the pwm signal. But the truth is : I don’t know how to find it…

How can I find it. I started to try with an LED, but I don’t now how to wire it.

More pictures of the board here : pwm driver | Flickr

PS : there is an Atmel Mega48PA on the board.

The RC circuit was probably the way to go. Motor drivers usually have a safety-interlock on
the potentiometer so you can't just remove it and inject a voltage, you have to disconnect the wiper
only and inject the signal there - with the pot (or an equivalent resistor) still in circuit.

Without such a fail-safe a broken wire could cause full-speed malfunction. A well-designed
controller will cut out if any one of the pot wires is interrupted.

But you also need to check that the pot is being used with a 5V range if you want to directly
interface a 5V Arduino to it.

If it were me I would check it with a scope and also ask the manufacturer for a schematic. I hope somebody can give you more help then I can.

The problem is that the driver is controlled by a potentiometer, not a pwm signal.

Maybe you could replace the pot with a digital potentiometer that can be controlled by an Arduino ?


Hi, thanks for your help all ! I tried to find where the pwm is sent to the mosfet.
I think I found it, but soon it didn't work anymore... Now it's full speed all the time...

Now I am thinking about using two smaller drivers...