I found a used hot tub online, that's a couple of years old and I decided I can make a cool project out of it. The built-in controls were already annoying and time-consuming, so that gave me further reason to tinker with it. In order to save energy, I lower the pool temperature when not used, but if I wanted to use the hot tub, I had to turn the temperature up 4 hours in advance. As an example of what I mean by saying annoying: In order to save energy, I had to lower the pool temperature when not used, but if I wanted to use the hot tub, I had to turn the temperature up 4 hours in advance. Another thing that happened was that somehow the circulation pump decided to turn on randomly during the night - that would probably have gotten under control if I had read the manual, but as a tinker I prefer to tear out the controls and use an UniPi 1.1 instead.
With the UniPi and running nymea on it, I was able to turn on/off each pump, set the hot tub mode "Ready" or "Summer", check the temperature and switch the blower. With the remote connection I can now preheat the hot tub before I come home and get a push notification when the hot tub reaches it's target temperature.
See the full project description here: