These range from building a DCC system for about $45 (see below) to a crossing signal. There are actually quite a few basic Arduino videos on the channel, although most of them are aimed at beginners.

[Johngineer] found himself in need of an I2C sniffer, but didn’t have one available. Necessity is the mother of invention, so he put together this I2C sniffer sketch for Arduino. The arduino … ...