Shaft encoders arduino - Rotary Encoder COM-09117 SparkFun
As explained in this post, rotary encoders are notoriously unreliable. Well, the cheap ones are. Why bother? But wait, could they be used at all? Most of the problems.
For the first generation of the INTRO Zumo robots, I have Pololu optical wheel encoders (see Adding Quadrature Encoder to the Zumo Chassis) which were available.
Rotary Encoder 1024 PR (Quadrature) Heres an arduino library for reading encoders that I found There is a tiny bit of notchiness as I rotate the shaft.
A Library for the Arduino environment for using a rotary encoder as an input. Here you can find an Arduino compatible library for using rotary encoders.
Most simple encoders like this only make use of 3 pins, and one of those is ground. From bildr article.
A rotary encoder, also called a shaft encoder, The output of absolute encoders indicates the current position of the shaft, plus how to use it with an Arduino.