The quadrature encoder with acceleration would seem easiest, but it still needs coding. My bright (I claim…) idea is to use two potentiometers connected to two analogue arduino inputs (method below), ...

I needed a rotary encoder — I pulled a cheap one out of one of those “49 boards for Arduino” kits you see around. Not the finest encoder in the land, I’m sure, but it should do the job.

Review of quadrature-encoder signals Aug. 1, 2004 The sensing mechanism in an incremental optical rotary encoder consists primarily of a light source, code wheel, and optical detector.

Quadrature encoder wisdom If you are a novice to rotary encoders for human-machine interface, there is a potential pit-fall. Otherwise called quadrature encoders, they deliver two-bit gray-scale ...