Spa controller

I added an Imp to my outdoor spa. Originally I wanted to intercept the communications between the main board and the control board, but I have been unsuccessful at decoding the protocol (probably SPI). In the meantime I added temperature sensors for the solar heater I built, air temperature, and water temperature, and relays to increase or decrease the spa temperature from the web. Since I can now control the temperature by software, I can take advantage of inexpensive off-peak power. A HUGE thank you to Hugo and team for making this easy and cheap!

I’ll post the code after I clean it up, but it’s actually very simple.

Temperature charts

Some of us have done a complete write-up on Instructables. It’s not as easy as you think to provide part lists, schematics, and clear instructions, but I think it’s worth the time it takes. People outside of this forum community might find your project very useful for other things besides spas.

Like all of us here, you’re now addicted to the Imp. Wrap this one up and get started on your next project.

Thats a great idea… I dont even want to know what kind of power my spa is using when it’s 0 degrees out. Mine is 220V… what kind of relays did you use? I’d love to see that circuit.

I used the 5v version of this reed relay with diodes from my parts drawer across the coils for protection. Although rated at 5v they work fine at 3.3v in my testing and they are cheap. One side of the coil is connected to ground and the other to an April pin. The terminals are connected to the control panel push button switches. The April/Imp is installed inside the spa under the control panel, which is a dry area.

I purchased waterproof 1-wire sensors for this project but decided to wait until the 1-wire library is available for the Imp. Instead I encased TMP36 sensors inside JB weld and then wrapped that in thick adhesive heatshrink tubing for extra protection. These are connected to 22 AGW wire in runs of up to 3 meters (for the solar heater). The signal is noisy, and I risk damage to the April due to induced current (I think) but it works.

My spa is also 220v and draws about 10KW when heating.

Whereabouts in the world are you? Seems like it’s lovely and warm during the day!

Southern California, where the brush fires keep us warm when the sun isn’t shining

My favorite hot tub weather is when the snow is falling on my head and I can smell the wood stove burning. That with a glass of Laphroiag 18 y/o scotch is pure heaven. :slight_smile: