Stefan Arentz, April 2021
This is a small program that you can run on a device like a Raspberry Pi Zero that will make LYWSD03MMC Temperature/Humidity sensors with custom firmware available on your local network as HomeKit accessories.
The LYWSD03MMC Temperature/Humidity sensors are pretty cheap. If you don't mind longer shipping times, you can usually get them pretty cheap. (Right now Gearbest has a deal for 4 sensors for $15 USD, which is a steal.)
For this to work you need to flash the LYWSD03MMC sensors with the custom firmware from github.com/atc1441/ATC_MiThermometer. Don't worry, this is easy - no soldering required - you can just install this firmware through a browser.
The current release is v0.5.0.
The easiest way to get going with this is to download the attached .deb file and install it on a Raspberry Pi Zero W. If you have a device that is a different architecture, please file a bug and I will update the build scripts to generate the proper packages.
$ wget https://github.com/st3fan/mijia-hub/releases/download/v0.5.0/mijia-hub_0.5.0_armhf.deb
$ sudo dpkg --install mijia-hub_0.5.0_armhf.deb
The default PIN for new devices is 122334455. You can change this in /etc/default/mijia-hub:
# Pin used to pair devices. The same pin is used for all
# devices. Must be 8 digits.
PIN="12233445"
Finally, start the mijja-hub daemon with:
$ sudo systemctl start mijia-hub
Follow the instructions on github.com/atc1441/ATC_MiThermometer. I was able to setup all my sensors through the web-based flasher at atc1441.github.io/TelinkFlasher.html. Unfortunately this only works in Chrome since Firefox does not support the WebBlueTooth APIs.
The following settings are important:
- Set the Advertising Type to Custom.
- To be gentle on the battery, set the Advertising Interval to 5 or 10 minutes.
That is all you need on the sensor side.
Once the mijia-hub is running on your device, it will listen on Bluetooth LE for sensors to advertise the temperature. Right now any sensor in range will be added, so if your neighbours are using these sensors with the same custom firmware, you'll be able to see those too. I don't have anyone else in range, so I did not care about adding an allow-list to the mijia-hub configuration - but if this is important to you, please file an issue.
The following two screenshots are from the Home+ application, which is an excellent replacement for Apple's Home.app.
