Desperatly seeking low temperature or power failure alarm for hot-tub. Any ideas on DIY or hacked comercial product?

I have a serious need for a sensor that either detects when my hot-tub temperature drops below a certain point, or when the electricity supplied to my hot tub is disconnected. A wireless remote alarm would be the best, but wired would also work. I found this need when the power to my hot tub failed and some of its plumbing froze. I am willing to use any microprocessor or even modify an existing device to fit my needs. The commercial versions are a little pricy for my budget. Any help would be greatly appreciated.  Is this a great place or what?

Burf6 years ago
I know Sper Scientific makes a low temp alarm perfect for a hot tub that runs around $20-$25 dollars U.S. You don't really need the power failure alarm in combination with a low temp alarm because you will know of the power failure if the temperature drops and sounds the alarm.
I believe you can get them from Amazon and directly from Sper Scientific.
Wire it all up with an arduino and some leds.
iPodGuy6 years ago
I have an oven thermometer that would do that very thing.
orksecurity6 years ago
Wired power-failure is easy. Use the power to keep a relay open; use the relay to control a low-voltage circuit for the alarm. The hard part is weatherproofing it.

Another alternative would be to put an induction sensor around the in-house portion of that power circuit, to detect current flowing through it and trigger an alarm when that stops. A bit more complicated; you're essentially building an induction ammeter. But it does avoid the weather.

Both of these are assuming that you're concerned about complete power loss. Detecting if just the heater fails would cover more failure cases. Temperature sensors certainly exist -- usually responding by changing resistance -- and you could set up a circuit which detects when that goes out of acceptable range. Again, this could be analog circuitry.

Wireless requires adding the transmitter-receiver pair, of course. I haven't played with that recently enough to have opinions about what's currently available/cheap/effective/suitable. Range between transmitter and receiver, and what materials will be between the two, affects some of those answers.