This 8051 microcontroller-based control circuit adjusts the speed of a small permanent-magnet dc motor via photosensors (see the figure).

To program these chips, [Aaron] first had to wire up the microcontroller into a circuit. This was just a bit of perf board, a resistor, a few caps, and a USB A plug.

He had previously created a simple communications system using his sound card that allowed him to send data to a microcontroller from his PC, but he thought that doing the same thing with light ...