Inside is Arduino Pro Micro and a PMW 3389 optical sensor on a breakout board. [Ben] was going to use flexible 3D printed panels as mouse buttons, but then had an epiphany — why not use keyboard ...

Pinout Arduino Nano Pinout Arduino Micro Pinout Arduino Pro Micro Pinout Arduino Pro Mini Pinout ATtiny25_45_85 PlayStation 1 modchip history PM‐41 (2) diagram PM‐41 diagram Programming via ISP ...