Cheap Wifi Thermostat with a JSON API
I updated my thermostat to one of these. It’s made by Homewerks (Home depot sells a filtrete branded version.) It’s not as cool as the NEST, but it’ll do the job of controlling a furnace/AC. The interesting part of this device is that the wifi interface can be cloud managed, making it possible to control the thermostat via my iPhone, iPad (or android) from anywhere with data connectivity.
It’s actually a fairly decent device for the money. It has a JSON api that allows you to get and set variables via web interface. There’s a fantastic PDF on the API that shows examples using curl (available on linux, mac, etc). What’s really interesting is that with a JSON interface, you could easily write your own application for mobile phones or just script up some commands from your choice of computing platform.
Wiring was interesting. On my ancient furnace (built by chrystler) I discovered some new details. The fan wire wasn’t connected at all! At some point, some A/C tech had installed a honeywell fan controller and the fan is activated by either the cooling or heating wires being engaged. (there is a manual switch inside the furnace. Argh!) However, I was able to re-use the fan wire as a C wire to deliver both sides of the 24v a/c transformer power to the thermostat. Wifi eats more power, and you need an external supply to feed that radio.
Setup is pretty neat. I loaded the radio thermostat App on my iPad, and once it discovered the thermostat, I had to join the ‘stats wifi network. Then I could configure my WPA2 network (excellent! Thanks for supporting proper protocols!) as well as a dynamic or static ip address. I opted for static the last time I configured it. –I reconfigured it a few times while I played around with wiring options.
The hardware in the device is rather interesting. It’s the first one I’ve seen with a wifi USNAP module. I’d expect to see more of these devices on the market. The price point is fairly low and the curl api is ideal. Hmm, arduino USNAP shield, anyone?
Resources:
Wiki (unknown owner) for developing: http://central.isaroach.com/wiki/index.php/Main_Page
PDF Documenting the Thermostat API. (local copy here) This is the interesting one.