Check out itub’s write up on GitHub for a Raspberry Pi controlled hot tub controller:
Raspberry Pi web enabled hot tub controller, supporting a heater (on/off or pool/spa control), air and water temperature thermistors, one two-speed pump, a second pump, (with hardware schematic). Includes freeze protection setting (run pump based on low air temperature) and daily filtering. Can continue to run pump (cool-down) for 15 minutes after heater is turned off.
Some design/development notes…
I built this project first years ago with an Arduino and WiFi (WiFly) shield. It worked well, as the Arduino has plenty of GPIO pins and enough analog pins to deal with everything. The most painful part was the Wi-Fi shield, and it’s (very) beta supporting code. I originally build the controller so that it polled an external service (the cloud!) to get it’s settings, and built an iOS application.
For various reasons (avoiding hosting fees among them), I decided to try this again, but change a few things to see if it worked out better: 1) Use a Raspberry Pi instead, and build everything in Python 2) Don’t use a cloud service — just host a web server on the Raspberry Pi itself. This requires forwarding a port and using dynamic DNS services to get it working, but that turns out to be Not a Big Deal.
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Each Friday is PiDay here at Adafruit! Be sure to check out our posts, tutorials and new Raspberry Pi related products. Adafruit has the largest and best selection of Raspberry Pi accessories and all the code & tutorials to get you up and running in no time!