This is was an experiment I played with back in 2016, to put a reclaimed 230V traffic light onto the Internet. Allowing a user to connect to a web page, click a colour on the user interface and the command would be sent via a websocket to a Raspberry Pi, which is interfaced over I2C to an Arduino, via a level shifter to account for the Pi's 3V3 and Arduino's 5V logic levels. The Arduino in turn is connected a set of relays and turns on the appropriate lamp.
This repo contains the source code of the Raspberry Pi nodejs program, the Arduino sketch and a fritzing schematic of how to wire it all up.
Below is a photograph of the experiment in action with an additional Raspberry Pi touchscreen display highlighting its multi-user functionality.
