Last month I started working on an electrical circuit project using an Arduino board. Inside a box I put an arduino board, and a breadboard for holding the wires.
There is also a relay module (2 relays – only 1 used). Sockets put on the box allow cables to be plugged in. The cables are (1) power, (2) a fan, (3) a motion sensor.

The whole project was intended to use a motion detector to sense when a cat used the litter tray. After they have left it turned on a fan for a few minutes which blows air through a carbon filter.

It took a few attempts but it works. How effective it is… well that’s open for judgement. Would be better if the fan could blow the air outside, but that’s not an option.