Dave Hunt’s bathroom didn’t have extractor fans fitted when the house was originally built. He decided to overkill the problem by having a Raspberry Pi control some new fans he fitted. He uses AM2302 humidity sensors to detect the moisture levels in the air. The readings get fed back to a Raspberry Pi in his attic which then controls the extractor fans via relays. In the picture above you can see the perspex plate the electronics are fixed to for mounting above the bathroom ceiling. Read more here.