The Ultimate Spark Core Hot Tub Controller

Two birds

For months our 25 year old hot tub has been out of service because the 4-step stepper relay started acting up. I took the controller apart, took the relay out and diagnosed that the spring that was supposed to return plunger to the up position was worn out. I searched the interweb for a new relay and the least expensive one I found was $192. Ouch. Not to mention that I wasn’t sure if the four steps on that relay matched the four steps on my relay.

I thought about it for a while and finally came up with a brilliant idea to supplement the spring with a piece spring steel that would lift the plunger back up after the coil pulled it down. I spent the better part of a day making, testing, remaking and retesting my idea until I came up with something I thought would work.

And it did… for about three cycles. After that we were right back where we started.

In the meantime…

Last year when I found out about the Spark Core kickstarter I thought it was the coolest thing ever. I wasn’t sure what I could to do with it but I signed up and contributed as much as I could afford… and then kind of forgot about it.

Several months ago I received all the booty that I was entitled to receive from the guys/(gals?) at Spark Core and it has been sitting a corner of my office unopened while I thought about what cool project I could do with it.

The Shower

I don’t know why but all my greatest ideas come to me in the shower.

This one was epic. I’ll use the Spark Core to rebuild the hot tub controller! I have the technology. I can make it better, stronger, faster. The Bionic Hot Tub!

My original concept involved using the Spark Core and its shields to replace everything. My booty from the Spark Core guys(gals) included a relay shield so I could use that. I already had an LCD display so I would use that. I have a temperature sensor so I can use that. I have an iPhone so I can write an app for that. It will be the best hot tub controller ever!

Of course, I’m not a programmer but hey, how hard could it be? Some of my best online friends are programmers. Besides, it’s open source.

The Reality

I have the original owner’s manual and schematic of our hot tub. Or so I thought.

As I delved into the rat’s nest of wiring that is our hot tub controller and tried to reverse engineer everything. I discovered that the controller that I have has an extra relay that is not shown on my schematic.

But hey, the basic functions are the same. I’ll just trace the wires… wait. Let’s back up a dang minute here. How about we just use the Spark Core and the Relay Shield that came with it to replace the stepper relay so we can get the hot tub running again and worry about all this other stuff later? Deal? Deal. Done.

It works.

The old stepper relay

The rats nest with the Spark Core with Relay Shield mounted behind it.

Some day I will get around to adding the LCD display, the temperature sensor and the iPhone app but for now I’m gonna go relax in the hot tub.

Thanks for reading.


cmon man, you can do this! at a minimum throw in a one-wire thermometer so you can see the hot tub temp from anywhere!
its super easy, and will be awesome. im rooting for you!

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$10 and you can monitor the temp