In my last post, I briefly wrote about the “Base Station” portion of this project. It will function both as a thermostat and a central point where multiple sensors report their data to. So I came up with a quick list of things this station needs:
- Display data to an LCD screen.
- Interface with a touch screen for user input.
- Use an nRF24L01 radio to communicate to remote sensors.
- Have WiFi capability (for internet connectivity).
- Turn the furnace or A/C on and off.
- Needs to fit into a box the size of the screen.
Way back, I bought a Raspberry Pi Zero to tinker with (who can’t resist a $10 board). It satisfies most of the points above with the exception of (1) being able to drive an LCD screen and (4) not having WiFi. For that, you need to use a Display Board to drive the LCD screen, which is rather big, and a separate ESP8266 for connectivity (or a Pi Zero W). This will not do.
So, after many hours of googling, I settled on a NanoPi M3 as the brains of the operation. MickMake did an episode on this particular board and gave it a decent review. What caught my eye was that it has an LVDS header built onto the board! This was the biggest selling feature of this SBC because I could connect my screen directly to it (well, almost). Built-in WiFi is great as well.
The screen is a Chimei Innolux EJ070NA-01J. It has a 40-pin LVDS ribbon cable which would require a PCB800182 converter board to bridge it to the 20-pin LVDS header on the NanoPi. I got the idea for the setup from a blog entry by Kailang Fu. The NanoPi and the converter board together don’t take up a lot of real estate in comparison to the Pi Zero and display board combo. I also purchased a capacitive touch screen (digitizer) which uses the FocalTech FT5306 controller. That particular chip has code available on GitHub and a linux driver. The hard part was making sure that its size matched up with the screen’s size, down to the millimetre. That required lots of research and datasheets.
Lastly, to turn the furnace and A/C on and off requires a relay module. The furnace, fan, and AC each have their own 24v circuit. There is an additional wire, called the common wire, that provides the power and all the thermostat does is complete the circuit.
More to come; stay tuned.