Thermostat Software

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EDIT: I don't profess to be a programmer, even though I can make my way through a few different languages. The code I present here works fine, but it's not very pretty or efficient. I think it's still useful from an educational standpoint and has a few ideas in there that are worth looking at and it's easy to get up and running. But I will soon be ditching this software in favor for some written by Wyatt Winters for his Rubustat (though I'll try to find a way to re-implement the checking of outdoor temperature to determine heating/cooling).

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In this post I explained that I tasked my Raspberry Pi with controlling the furnace and air conditioner in my house. Here I describe the software that went into it.

The requirements I wanted were simple enough:

1. Behave similarly to a commercial thermostat
2. Schedule temperature set points
3. Automatic switching between heating and cooling based on outdoor temperature

Sous Vide Part 2: The Early Version

In part 1 of this post I talked about what sous vide is and a little about how it can transform foods. I'm not going to delve into the world of opinions on how fantastic it is, unlocking unheard of flavors, tenderness beyond belief, etc etc. I assume that if you've come this far on the internet you've already read a lot about all that, so I don't need to convince you. Instead, I'll lay out my experience tinkering with my homemade controller, how I did it, and how you can do it, too.

Raspberry Pi Thermostat Hookups

I recently replaced my thermostat with my Raspberry Pi. In this post I explain how to make the hardware connections between the Raspberry Pi and the house wiring. Check out the Makeatronics Store if you want a PCB that does the connections for you.

In my house (and the vast majority of others) the thermostat wiring runs at 24V AC. There's a live wire (or two, depending on the setup) coming into the thermostat, and several others leaving to control the different components of the HVAC system. The thermostat's job is to close the circuit between the live wire and the appropriate control wire based on the temperature. A relay is an easy way to do it, but I find relay's cumbersome with their (usually) breadboard unfriendly pin layout and larger-than-can-be-supplied-by-gpio switching current requirements.