a turntable embedded on a PCB, a silkscreen on a round PCB to encode the position using gray_code

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github repository

tools used

inkscape
extensions

kicad

Layout

digital

analog

a few guides and approaches

Gray code

wikipedia

“to get a gray number only change one bit”

http://datagenetics.com/blog/november32014/

components


other methods

the following are for reference

LED as light Sensor

no word regarding detection speed

magnetic

Magnetic_vs_optical

DC motor

simply connecting a dc motor to the spinning disk
by rotating the disk you convert the energy to analog input for MCU or whatever
problem with this approach it will not give enough output at slow speeds. so probably scratch that.

Stepper motor

same as with the DC motor, you connect the motor to the disks center, then hook the stepper winding A1/2,B1/2 to an MCU, you get a nice stepping encoder.

following links are actually to use the sinusoidal wave of the stepper, a bit of a different approach
also a problem at low speeds.