Hot tubs (again)

Hi all
This is my 1st post and I confess to being a complete novice.

We have a hot tub that works perfectly well. It’s running a Balboa M7 logic board which gives 3 operational modes
Normal - Temperature is maintained by a 4 hourly heating cycle
Economy - Temperature is maintained by an 8 hourly heating cycle
Sleep - Temperature is not maintained, except for frost protection

Temperature information is provided by 2 x temperature dependant resistors, one each side of the heater element. I have the specifications of the resistance / temperature curve.

Scenario, we mostly use the tub at weekends. I want a custom heating cycle without impacting any of the other normal processes provided by the Balboa controller.

My idea is to use an Arduino uno to ‘spoof’ the controller by replacing the tdr with fixed value resistors from Monday - Friday which will tell the Balboa that temp = ok, do not apply power to the heater.
Friday afternoon - Sunday midnight, switch the fixed value resistors out and switch the standard temperature dependant resistors back in.

This is just a very early idea, I may wish to utilise the analog inputs to read the tdr values and do something more exotic later.

I think I will need the following:

Arduino uno, relay block (latching ?), fixed value resistors, timing routine

Thoughts, comments, suggestions welcome


That sounds like a complicated way to turn the power off Monday-Friday. A timer switch would do it much more simply.

If frost protection is actually necessary in your area then I suggest you don't mess with it. Frozen pipes will cost a lot more than the electricity you might save monday to friday.

If you don't need the frost protection then just unplug the thing.

I agree that dropping the power via a timer, would be a simpler (though somewhat brutal) approach. However with the power down there is no circulation, or filtration going on. I'm also unsure of the long term effects on the existing logic circuitry of switching the mains off and on again once a week.

I was hoping for a more elegant solution that I could use as a basis for a more sophisticated system in the future

Well, if you have any questions, we're standing by to answer them. Until you have something that you can write as a sentence that ends in a question-mark, we're just being social.

As this forum is for general project guidance, I was looking for exactly that.

Is there latching relay available for the arduino ? To achieve what I want, the coil would otherwise need to be energised for around 60 hours
As I'm only switching 5v signals, is there a better way to achieve this (if so, what ?)
Is there a suitable timing routine already available ?
Has anyone done something similar ?


Please describe exactly what you want to do and how you think it should be done. So far it appears that a simple time switch would do the job. We would like to know what you are thinking.