Electronic Circuits - interfacing with an arcade game
Having already built a small Nintendo NES interface which I used to control Super Mario Bros. with a BASIC program running in Snowdrop OS, I thought I'd extend to the realm of arcade games.

Arcade games were almost mystical to me as a youngster - they were beautiful, imposing, captivating, and took my money.

This project involved a simple wire-up (plus experimentation) between my parallel port interface and the player input pins of my arcade cabinet. The software part was also easy, consisting of a simple Snowdrop OS BASIC program to output logical 0s and 1s to the parallel port, according to keys being pressed.

This is my "general purpose" parallel port interface board. Each parallel port pin is optically isolated from the output circuit via a 4N33 photodarlington optocoupler.

In this application, each parallel port pin acts as a switch between the arcade board's positive voltage pins for an arcade button, and the arcade board's ground pin(s).