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.