Wireless HVAC Sensors - V3 now available

At last we have it. V3 of my wireless HVAC sensor board has been tested and the hardware is done. There were some tweaks to the board over V2, one to fix a mis-routed trace and several geometric improvements to get it to fit inside an electrical box. And now all is well.

Wireless HVAC Sensors - Part 2

Previously I introduced the idea of a battery operated wireless sensor board for sensing temperature and humidity. The intent is to get information to my Raspberry Pi (or Arduino, or any other microcontroller) so that it can intelligently control the HVAC system in my house. Today I give you an update on the project.

Wireless HVAC Sensors (temperature and humidity)

As I've been working to transition control of my HVAC systems over to my Raspberry Pi there has always been one big hurdle to overcome: how to I get the temperature reading from the room I'm interested in to the Raspberry Pi in the basement?

24V AC Solid State Relay Board

My post on the hardware connections between my Raspberry Pi and HVAC wires has become one of my higher traffic posts so far. Apparently people are searching for ways to connect Raspberry Pi's to thermostats (or Arduino or any other microcontroller for that matter). So I decided to design a circuit board to fill that space.

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

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.