Had a bit of fun in the shop over the last few evenings. My friend Matt who comes by for workshop wednesdays has been working on some home-built machines. This time he showed up at the shop with a DC motor and its control board from some 25 year old treadmill he found by the side of the road. (Why do I have these indelicate electronics on my metal bench? I just noticed now. I plead idiocy.)
What an ugly thing. The good news is that the motor connection is right there in the middle of the board. And it's old enough that it's probably simple to reverse engineer enough to get some signal out.
The "digital" end, such as it is, is a PWM generator - theres a chip in there that takes a voltage level and turns it into a PWM signal, which is then conditioned somehow through all the goo on left. So that means there's a power transistor somewhere switching the DC power.
And there it is, dangling on the right with its three terminals.
![1681488617829.webp 1681488617829.webp](https://canadianhobbymetalworkers.com/data/attachments/41/41283-0fa1e28d8d67512e2bb59540850935ec.jpg?hash=cVJaQawcHs)
And oddly, it's connected to this funny little island of logic. Why, there at the very bottom is that little 6-legged package that claims to be an opto-isolator! They've separated the PWM generation end of the board from the power end! That's a blessing for doing this job - I don't need to start chopping a pile of traces to isolate the PWM driving. And it means I can connect my own Arduino-based PWM signal to *just* that opto-isolator. So I wired it up with aligator clips, with a potentiometer on the Arduino to control the PWM, and...Nothing.
So more digging. Turns out, of course, there's a big relay (the big black block in the middle of the board) that needs to be controlled to turn on the DC power. And I figured this board was simple enough that one of the lines on the RJ-45 connector would control the relay, and yeah. First try poking a ground wire at the connector found the line, and there was even a handy pad to wire to ground to pull the relay open. Win. And now the motor runs, and varies speed with the potentiometer.
A bit of tidying left to do, but there's a few good places to tie the opto-isolator lines to the board, and it's getting less ugly. I was even able to power the Arduino off the 5V regulator they used for the digital end of the board.
I'll get some shots again when Matt gets all this mounted tidily in a case.