I have a couple optical joysticks that Ill be porting over using a teensy2.The comments here are on track. The joystick has 2 lights on the bottom of it. and 2 photodetectors, one is directly below the lights, and the other is at a 75 degree offset, and slight offset from center. I think the lights are the same colour, and they are in series. moving the joystick in any particular direction will cause a variation in intensity. center is brightest on e1 and 50% luminous on e2. hard right is e1, dark, e2 dark, hard left is e1 dark, e2 bight. full forward, and full back, are varying intensities, on e1,e2. The teensy2 has 10 bit analog. I should be able to make 1024 unique comparisons pretty easily. The 2nd eye being offset from center was a good observation for my use. it means the circular motions of the joystick produce an elliptical illumination pattern.