mouse encoder

Old ball-type Mice make perfect resources for rotational encoders. There are however numerous different sensors. Some have plain photodiodes, some have IC’s which do part of the converting to TTL signals. Last is the case with plain old logitech mice (the ones with encoder wheel). Simply hook up the first two wires to Vcc and Gnd. The other two are your A- and B- phase (to feed into your microcontroller)

An other resources for mouse interfacing is here
On my to-do list are trying to interface non-ball mouse sensors too (see here)