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Sunday, February 14, 2021


I made a little wifi high-precision temperature sensor as part of my stalled thermostat project a while back. Here's the temperature in our bedroom with the heat pump running continuously:

The drops happen during the automated defrost cycle.... Do you see a problem? (And yeah, that's date/hours:minutes at the bottom...) It wasn't even *that* cold outside... (just a little below freezing at this time I think). This is why I need to make my own thermostat. (Clearly it shouldn't be running the heat pump at all at this point. Though I wish the heat pump provided more direct control of the defrost cycle as that whole thing is poorly done and needlessly noisy, and it's possible I could eek significantly better performance out of it with better timing.)

I wish I had installed the power tracking already because I want to see if this is with or without the heating coils engaged. If it is with, then the heat pump is behaving more like an A/C on net and not only wasting energy running but actually pumping the expensive heat coil heat outside.... (And if it's without, then my thermostat is broken.)

I already built my own thermostat (took an afternoon and $20 in parts) but was too chicken to install it heading into winter. :)

But after learning enough of how it all works to see how dumb things are, I'm increasingly keen to build an open source thermostat done right (HestiaPi doesn't have enough relays and is way more expensive than it needs to be). If any of you hardware hackers want to help me design and mass-produce populated custom PCBs, let me know.

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Simon Funk / simonfunk@gmail.com