Here’s a massive project for you. Normally, pool automation systems cost somewhere in the region of $10k. So, an Instructables user decided to create his own using a Raspberry Pi. He hooked up all the inputs for the main swimming pool and the adjacent spa pool to relays and then had the Pi control them. He then built a web interface for it to enable him to control and set-up the two pools via his smartphone. 60 hours and a comparatively minor $1000 later, he had a fully working system. You can follow an overview of the project on Instructables and see a video of the main pool control below: