While newer Arduinos and Arduino compatibles (including the Hackaday.io Trinket Pro. Superliminal Advertising!) either have a chip capable of USB or rely on a V-USB implementation, the old fogies o… ...

Specifically, [ElectroBoy] uses the AT89S52. Like the ATmega microcontrollers, the AT89S52 has an 8-bit CPU with a Harvard architecture and very similar GPIO capabilities.