Wyostat: Open Source Thermostat Pt. 1




Does the world need another connected thermostat?

When my thermostat went on the blink last winter, I looked at Nest, and Ecobee, and the other me-too thermostats, and I decided I would rather build my own.

  1. If Nest goes out of business (or even more likely, Google decides to go a different direction),  all that cool connected functionality pffft!
  2. If I want to control it just inside my house, I don’t really have that option.
  3. Some of the connected thermostats also offer remote sensors, behavior learning, etc. but they are expensive, and you have no control.
  4. I have a two wire system. While some of the connected thermostats do power stealing (Nest), I wanted more powering options.
  5. I’ve been playing with ESP32’s and I’ve found them powerful and cheap!

Prototyping

Most home hvac systems run on 24VAC. When I moved in to my house, it had one of those classic round bun thermostats that tilt a mercury switch with a bimetallic spiral. More modern systems have an additional C wire for power (and separate fan  and cool wire). This meant that I would be powering the thermostat externally. A little googling and I found this info on thermostat wiring:

I found a triac board offered by another maker and open source enthusiast:
http://makeatronics.blogspot.com/2013/06/24v-ac-solid-state-relay-board.html

Wyostat Open Source Thermostat Pt. 1

It features three triac channels with Opto-isolated inputs. The control signals seem to work at 5V or 3.3V.

For the controller I found a dev board with an ESP32 module, SiLabs usb controller, and a small monochrome OLED display. It’s sold as Wemos Lolin, and it has a Wemos-like logo on the back. it’s actually a clone of a D-Duino-32 by Travis Lin.

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Wyostat Open Source Thermostat Pt. 1,




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