Cheap and cheerful.

Abstract: This paper presents a precision capacitive rotary encoder that integrates a shared charge amplifier, and a multi-stage offset calibration scheme. Recently, capacitive encoders have gained ...

// can be found in many places. // For example on the Arduino.cc forum. // The original author is not know. // Version 2, Juni 2012, Using Arduino 1.0.1 // Adapted to be as simple as possible by ...