raspberry pi
A family of single board computers. It serves as the "brain" on 3615-YouTube, wordblitz-plotter and gml2mt.
GPIO
GPIO pin numbering from pinout.xyz
The General Purpose Input/Output pins are 40 electrical connectors that allows the Pi to communicate with other devices. They can be used as digital input/output (3.3V/0V), with some pins supporting Pulse Width Modulation (PWM). There are however no analog inputs.
The RPi.GPIO Python module can be used to control each pin individually.