I started with the hello.light.45 board, but used two optical interruptors/Photomicrosensors (Transmissive) EE-SX1103 instead of the usual phototransistor.
Became messy pretty soon -- needed a bigger board with more traces.
hello.optical.keywon board
Next, I extended the board to accommodate 2 optical interruptors, and tentatively named it hello.optical.keywon.
Mounted the sensors on a lasercut cardboard disc.
Oscilloscope reading from the collectors -- picture and a video.
I uploaded a modified version of hello.light.45.asm and plotted the readings from PB3 and PB4 pins using hello.light.45.py, but it only shows one graph for two readings.
To do next:
Further modify hello.light.45.py to show a plot like below.
Count teeth on the disc and get relative angle change
Set start angle (capacitive sensing? another optical interruptor?)