HVAC Thermostat Dev Blog

• https://github.com/andygock/avr-uart/blob/master/uart.c

• AC Dimmer circuit

Been working on getting a wifi sensor setup and configured. Got the ALS setup pretty simply, just reading an analog value. Then started work on the BMP180 sensor. Had to write the i2c class interface and then re-writing most of someone else's implementation of a BMP180 class. Using the docs for the bmp180, it took some doing to get it right, but it's now working. Some of the issues were getting the right combination of i2c commands, start/stop/restart, working then the other issue was with the pressure value being to big for the data type they were using. So now the barometric pressure and ALS work, so does the DHT22. I need to do some work on making the DHT22 more accurate, using a kalman filter or just a simple average.

So I've created most of the HVAC Controller and I am using a Darlington Array to switch some relays. It took me a while to figure it out but I finaly realized that the Darlington Array switches to ground. I may have the IC of the array power inversely which may be causing this but once I realized that the relays needed a positive feed and then go to the Array, everything worked.

I have also added two more relays to support the use of the heater. Before I was just using the fan and adding humidity to the air. Now I have added the functionality of the gas heat to work. That took a while since I was trying to use the high gas and that is not connected apparently. Also, when I would turn on the low gas the flames would pool out of the furnace. I realized it was due to the draft fan not being turned on. Once that was on everything works like it should.

Finished building the board with all of the control relays. The obvious issue was that the microcontroller isn't supplying enough amps to power all the relays. To cheat I added a cap.

Well, I broke the HVAC controller board in the furnace because I was trying to get the humidifier to work whenever the fan was on. So, the board is now toast. I started work on the components, it's a fairly simple design in that there is a microcontroller controlling relays. That's pretty much it.