So you have a nice little motor and maybe you want to turn it into a robotic project but, alas, it doesn’t have an encoder built into it cause it’s a cheapy thing you found at a swapmeet. Prof. Mason has a nice and simple solution that you can make for $5 and retrofit yourself: a magnet and two hall effect sensors. I bet if you used a Schmitt trigger’d comparator on the outputs you would have a pretty effective encoder that can go straight to your robot brain. I imagine this design is less finicky than optointerrupts + disc. Don’t forget to plug the signals into the microcontroller interrupt pins because they’ll be flying by rather fast!
Is there such a thing as a magnetic set-screw shaft collar? That might avoid the uneven weight problems of gluing a big magnet on.
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.