I recently got a few of those rotary encoders – I was planning to make them into a follow-focus system. It’s a two part process: 1 – make a USB interface for them; 2 – make software that uses Canon’s EDSDK to interface with my camera.
So I decided to start on 1, then I got a bit carried away and got this monstrosity made – an Etch-A-Sketch for computers, because everything deserves rotary encoders.
If you look very closely, each of the encoders has it’s own plug, since each is a independent USB HID device.
Next step for the monstrosity, given that I now have two computer-connected knobs side-by-side, is Pong. And then I can return to the original plan of making a camera accessory.
Yifan Gu's Blog 