A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code. (from wikipedia)
There are a few of these rotary encoders available in the space for use with your project. It's electrical rating is 5V 0.5mA (very low, not even a LED driver!)
Here is the  The pinout is, viewing the encoder from the top, 2 pins up, 3 pins down: A C B. The 2 terminals on the up size are push-to-make.
Terminal A-C leads, i.e., when rotating clock-wise, A-C will go 'on' first, then B-C will go on, A-C goes off, then B-C goes off. Counter clockwise means: A-C goes on, followed by B-C which goes off.
|rest (0°)||~3.75°||~7.5°||~11.25°||rest (15°CW)|
In short: on falling edge interrupt A-C (which is the dented position, in a 15±3° step), B-C high means a clockwise step; 24 steps make a circle.
Location: Somewhere (probably somewhere in the racks on top of the soldering table)