If counterclockwise, the DOWN signal is registered at each step. Luckily, using the mouse scroll wheel encoder with an Arduino Uno proved to be easy after I made a slight modification (see below).

Every single (non-optical) mouse comes with a pair built in. On either side of the encoder wheel are some little boxes. One side is an IR emitter, and the other side is a pair of IR detectors.

Start with a standard optical mouse with a fairly small footprint. ? Take a photo of the pcb layout to trace the tracks if needed. ? Remove the microswitches and the wheel encoder. ? The ring from ...