Do I have to build my own touchscreen thermostat?

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They have their own microcontrollers usually to manage that stuff, including defrosting

AwkwardLookMonkeyPuppet

Honestly, that's how competent programmers look at just about everything these days, especially junky-ass websites that probably couldn't violate more best practices if they tried.

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If its a cheap crappy one, the compressor is on/off depending on temperature. Decent ones will have a VFD to manage the load of the compressor so it doesn't have to turn on/off all the time but just regulates the compressor load to match heating/cooling requirement. Both have their own controls, and you generally shouldn't mess with them.

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Heat pumps are not simple at all. They are extremely efficient but can’t produce a large temperature gradient so they need to run very long cycles (potentially remaining on 24 hours straight). Modern cold weather air source heat pumps also tend to have variable output (variable speed compressor, variable speed fan). This demands a more complicated thermostat that adjusts the heat pump up and down, possibly with PWM.

And then there’s the emergency/auxiliary heating from the furnace. The thermostat needs to have some intelligent logic to decide when the heating demand exceeds the capacity of the heat pump and call for the furnace.

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If we're on this subject, do you happen to know any active esp Lemmy communities?

thanks and merry christmas

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Heat pumps are an entirely different story, and I don't have too much experience with them, most of the splits I've seen come with their own remote controls. I was talking on more traditional wall heaters, central air/furnace/forced air, etc.

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Most programmers (those doing fancy GUIs and C# programming on a PC) would be seriously out of their league if they ever actually tried to program such a thermostat. Or any other embedded system. You really need a special skillset and hardware knowledge to even get a simple embedded system running. This is what my trainee just learned the hard way in the last weeks...

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Yes, the C/blue wire is common, basically a neutral for the 24v system and necessary for more digital thermostats to keep the thermostat powered (some can work without the c wire, but it depends on the unit feeding power). The old mechanical ones work on the tilting mercury thing or copper coil for temp sensing, and only require the red wire to touch their respective wires to call whatever function, but the digital ones do the same thing on a switching level. I know there are additional wire sometimes for multistage heat and zoning, but as far as I know it's the same principle. I'll be honest I'm an electrician by trade and not an HVAC guy, and I know some of the more intricate systems can deviate from this, but your average residential system should be similar or damn near the same as my original comment (granted my experience is in Southern CA, so there are possibly regional differences with oil furnaces, radiator systems, etc).

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Everything is laugh and giggles until the thermostat is turing complete.

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"Smartknob View"

Sabata

Tape a raspberry pi to the wall with some relays and a temperature sensor dangling and call it a day. Anything else is spying on you.

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Except thermostats. You literally could do it with a Raspberry Pi, some 24V relays and a temperature sensors. Thermostats are not that hard.

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Inputs and outputs mapping sure is hard /s

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Program it in increments?

My house has a lot of thermal mass. In the morning when the temperature comes up, it tends to overshoot after working hard to heat all that thermal mass. However I found it much more comfortable to add an increment: half an hour at a degree colder than I want. Now it can heat all that thermal mass while overheating the air is just playing into my hands

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I’ve got it programmed in increments of a half a degree per hour. The thing still goes into panic mode.

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It’s actually surprising that we expect so much from a smart thermostat. Wouldn’t it be far smarter to sell a dumb thermostat on a local iot network and put the smarts in your automation hub? People who want the extra functionality would be good with that and people who don’t would appreciate saving the money

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If my choices are a z-wave/zigbee thermostat that connects to my HomeAssistant instance and a Raspberry Pi that I have to maintain, I'll pick the z-wave one (and I did, 10 years ago. It's been rock solid.)

For my smart devices I prefer devices that can't send information over the internet no matter what. I don't want to worry about my thermostat mining bitcoin for some dude in China.

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A smart thermostat is the only smart device I own (ecobee). I figure it actually is better than something I could design in a week so it seemed worth it. Do you know of an actually competitive open hardware/open source solution?

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Smart thermostats do way more than just set the temperature: that's table stakes. Off the top of my head the ecobee will:

Set the temperature also taking the room's humidity into account
Communicate with sensors throughout your house
Can change things via the Internet in case you accidentally forget to set it to a better temperature when you'll be gone for a few days
Tweak your schedule based on demand

I'm probably missing things, but they're actually pretty useful, and I'm someone who thinks most IoT is shit.

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Well that's not quite true.

I have some z-wave thermostats, which I know do not talk to the Internet, just a local system with a zwave dongle.

For a relative, recently set up a similar setup, but with a homekit thermostat. Similar deal, though it really really wanted to connect to a cloud server and you kind of had to trick it to a non apple homekit setup. The follow on model from that brand did drop homekit support, presumably because they wanted to force their cloud servers, which became required for any advanced functionally.

There are ways to get automation friendly devices without a cloud connected requirement, though admittedly you have to be paying pretty close attention. Generally offerings for business are more likely to be locally workable, but that's hardly a given either