Project: Boiler Automation

Building a smart central heating and hot water controller with an Arduino, a Pi Zero W and Home Assistant.

The Brief

My study/workspace is in the basement, which can get cold. The central heating button is two floors up at the opposite end of the house. I wanted a cheap, non-invasive device to press the button via a friendly web UI!

The Plan

Actually use one of the many Arduinos I have lying around (a 5V Pro Mini in this case as I was going to add an external regulator).
Press the central heating and hot water buttons with using servos, with the 'fingers' resting in a retracted position so the buttons can still be reached.
Read the central heating and hot water 'on' lights so it can report the status if changed manually.
Read the temperature and humidity of the airing cupboard the boiler controller is in (as I also have plenty of DHT11s lying around).
Communicate with the Arduino using nRF24L01+ 2.4GHz transceiver boards using RF24Mesh, as I was interested in adding other devices to a house mesh network.
Set up Home Assistant as the friendly web UI and write a device plugin for it, running on my Kickstarter-backed UP² home server (yes, I backed a hardware Kickstarter and it actually made it to production).

What went right

To try new tools, I used PlatformIO on VSCode on macOS, which is an excellent setup for development on multiple connected Arduinos.
Controlling the servos using the Arduino PWMs was a doodle, as was reading the lights with LDRs.
Making servo/LDR mounts and button pressing 'fingers' is also a doodle if you have a 3D printer.
Added a beefy 5V regulator to power the Arduino, servos and transceiver.
Managed to get the nRF24L01+ boards registering with RF24Mesh and communicating Arduino to Arduino.

What went wrong

Initially couldn't get the nRF24L01+ boards to work at all, even with the recommended passive components on the supply, and thought I'd managed to pick up a batch of dodgy copies that had the ACK bit flipped. Bought a power breakout adapter for my breakout adapter that came with its own 3.3V regulator and the passive components on a PCB which seemed to solve the issue.
With the nRF24L01+ boards communicating Arduino to Arduino, the boards could not reach the distance required, even with the transmission power at maximum and the bitrate reduced to 250kpbs. Replacing them with nRF24L01+PA+LNA boards (that were thankfully pin-compatible with the power breakout boards) solved the range problem.
RF24Mesh supports running the master node on Raspberry Pi and Linux with a number of IO drivers, so I thought getting it running on the UP² would be simple as it is Pi GPIO compatible. Not so much. Submitted a pull request to get it building correctly with MRAA, but even then it wouldn't remain connected for more than 30 minutes without sporadic GPIO timeouts. Gave up.
As I'd got the Arduino to Arduino communication working, thought the I could attach the nRF24L01+PA+LNA boards to an Arduino set to behave as an I²C node to the UP². Built a 3.3V to 5V level-switching board with pull-ups for the I²C bus between the Pi and Arduino, not strictly needed as I²C pins are high impedance, but didn't want to risk blowing the Pi up if I accidentally set the pins wrong. Tested the I²C communications with a PCF8574P (again, lying around) then implemented the Arduino as an I²C node. Worked. Attached the nRF24L01+PA+LNA. Still unreliable. Gave up.
Was so close to completion but couldn't determine whether the 2.4GHz communication problems were the beta-ness of the mesh network library, electrical noise from the boiler or servos, being overpowered by other local WiFi hubs, dodgy Pi GPIO compatibility on the UP², my ineptitude or a combination of them all.

What went right (finally)

Replaced the nRF24L01+PA+LNA with a Pi Zero W, as I have perfectly good WiFi in my house, communicating with the Arduino via I²C (phew, the code and Pi-to-Arduino board weren't wasted).
Found out you can power the Pi via the GPIO 5V pins, admittedly bypassing the fuses, so could run it off the existing 5V regulator.
Wrote a simple web API for the Arduino with Flask, which I ran as a single-threaded single process so I didn't have to think about shared resource management and locking access to the I²C bus BECAUSE I JUST WANTED IT FINISHED.
Installing Home Assistant on the UP² and writing a switch-derived custom plugin was easy. It has good documentation and being on GitHub you can read the code of the existing plugins.
Configured Home Assistant security and port-forwarded 443 (SSL with Let's Encrypt of course) to the UP² so I can control it on the go!
Even with the unused transceivers, the whole device cost about £20.

Conclusion

It was a fun and practical project that has made my life better (lazier) and even my other half thinks is incredibly useful. So glad to finally find a use for a parts I'd bought thinking 'they would be useful'. Spent way too long with the 2.4GHz transceivers, just because I liked the thought of a house mesh network. Will try them again for future outdoor projects and use a programmable WiFi chip (like an ESP8266) for indoors.

What's left

It's been working well for a while now but there are a few things that can be done:-

tidy and publish the Arduino, Flask and Home Assistant plugin code.
make the cables a bit less chaotic looking.
replace the gaffer tape with a better way to mount (and dismount) the board.
replace the cable ties fixing the controller circuit and Pi to the board with something less dangly.
move the DHT11 so it isn't just taking the temperature of the 5V regulator.
disable the boiler timer and control the schedule with a Home Assistant plugin.
add wireless thermometers around the house to Home Assistant so I can tune the radiator thermostats and possibly get Home Assistant to control the heating to maintain a set temperature.

Posted Mon 19 Feb '18 in Build