andrewmccluskey, hynni2,
12/25/18 - Ok, here's my treadmill project....... The details may provide some insight - I have a Spirit Esprit ET-8 Treadmill, and the top board that runs the console is fried. The bottom board:
https://www.amazon.com/Sole-Fitness-Controller-Transformer-Treadmill/dp/B07K5K1YK9 - that controls the belt speed and incline works just fine.
There's a 12 pin cable that runs from the lower board up to the upper board console. Coincidentally, and what I expect is fairly typical, the pin layout referenced in this thread above is *identical* to the pin layout of the 12 pin cable in my treadmill and may be similar or identical to what you have:
1 - S/W - 17 Volt
2 - Dwn -.086volt
3 - Up -.086 volt
4 - VCC - 18 Volt
5 - Fast - 5 Volt
6 - Slow 5 volt
7 - Grnd -.098
8 - Spd - 5 Volt
9 - Spd - 0 Volt
10 - Vr1 - 5 Volt
11 - Vr2 - 5 volt
12 - Vr 3 - 0 Volt
Now, to control the treadmill - jump 1 and 4 together for power. Then A) Make Break 5 and 7 over and over to increase speed in .1 mph increments. B) Make Break 6 and 7 over and over to decrease speed by .1 mph increments. C) Make 3 and 4 together to incline the treadmill. D) Make 2 and 4 to decline the treadmill.
I have put 4 push buttons on the treadmill console that perform those four A-D functions.
Now, I'm going to do that A-D with Arduino Uno along with adding additional functions. Instead of speed increments/decrement of .1 mph, I'll make that .5 mph. Also, will add 5 buttons to take speed right to 2, 4, 6, 8, 10 mph. Will also add 7 segment leds to display speed and incline amount.
I'll post more as this progresses, but hopefully, there's something here you may be able to move forward with.
12/26/18 - One note from reading through the thread - a pot is *not* used for any of above. Just Make Break the circuit of pins 5-7 to increase speed, and Make Break the circuit of pins 6-7 to decrease speed. The intro arduino push button solution for that is pretty basic. Connect pins 1 and 4 to the magnetic emergency switch of the treadmill.
I believe that pins 8 and 9 are used for pwm speed control. In normal operation, this is how speed would be adjusted, and pins 5 and 6 would be used internally by treadmill to adjust speed in small increments when magnetic belt sensor reading does not match user selected speed. I will need to test in a day or so.