pinball
This is the source code for a project that my friend and I decided to build our senior year of high school. We scrapped an old pinball machine for parts, and used an Arduino and a relay to control those parts.
Most of the code is very specific to this project, but code in button.cpp, button.h, output.cpp, and output.h could be used in other projects. Though I would suggest looking at the other file for examples of how to use them.