I got an old keiser stationary bike (M3) and I am not using it much.
I’m going to try to mod it up a notch and install some esp based computer on it that can do Peloton-ish things, maybe implement a standard data feed for some existing biking apps. Maybe it’s going to motivate me to exercise some more.
This is work in progress, just recording it here in case someone wants to independently tinker around.
The good new is that the keiser is built like a tank. It’s relatively easy to take apart and put together again. However, there are some screws that are hard to put back (e.g. bolts around the pedals - I had to do some remedial dremeling to access the space to put the counternuts back in place. I also got a leftover bolt which I couldn’t place).
The bad news is that the bike computer is bit of a mystery. I couldn’t make much of it with an oscilloscope (because I’m crap at using one). However, after taking the bike apart, I came onto the little board that gives data to the bike computer, and the sensors could not be simpler.
THere’s a reed switch that triggers once a resolution, and wakes up the bike computer. This is obviously required for cadence.
There’s a pot (looks like a 10KOhm pot) that is moved with the resistance (low resistance = low gear).
the bike computer has 2 AA batteries, so runs at about 3V.
the board is connected to the computer with a data cable that has 4 strands, black, red, yellow, green with plugs at either end incredibly helpfully named “black”, “red”, “yellow”, “green” on the PCBs.
it looks like that the pot is between the yellow and red strand, the reed switch between green and yellow.
More details as I get more time to tinker. In the meantime, there’s more detail in the “Keiser M3 User And Service Manual” which can be found online using a search engine.
Also interesting: This project to instrument the same bike model with a motor to automatically adjust difficulty level.
Written on August 17, 2020