I made some (good) experiments not with optical encoders, but with Hall magnetic sensors and magnets from old HD drives. The Hall sensors are sufficiently linear with respect to the magnetic field, their output is from nearly 0 to nearly +5V. I connect them to th M-JOY16 (Mindaug Mindauskas project), and they are working fine. But - I used it in my home construction of rudder pedals, not as a direct replacement of existing pots in existing joy.Petr