Xiaomi Mijia Temperature and Humidity Monitor 2

Bought a few of these to place around the house to check the temperature once in a while.

Xiaomi has released different temperature and humidity sensors, but the ones I got are the LYWSD03MMC model. Instead of a AAA battery, these uses a CR2032 battery, which is included. Just pull out the clear plastic tab to turn them on.

First impression is that these things are deceptively small (43 x 43 x 12.5mm). The marketing pictures always make them look like they're as big as your hand, while in fact, you can probably fit 3 or 4 of these on your palm.

The square LCD display shows the temperature and the humidity and a smiley face and not much else. You can use the Mi Home app to view historical data and supposedly integrates with home automation hubs / IFTT to switch on humidifier when indoor humidity is too low or air-conditioner when indoors temperature is too high. Me, I just want to know the temperature.

Looks like these Xiaomi Mijia sensors are popular enough that someone took the trouble to hack them. Can use this to flash custom firmware on the device to unlock additional customization options.

The neat thing about the project is that everything is done over-the-air on a browser. No need to open up the device or make any hardware changes.

Everything is explained in detail on the Github page, but in summary:

1. Use a browser to access the webupdater page
2. Press "Connect" and pair with the target device once detected.
3. Activate, then flash custom firmware, which takes a couple of minutes.
4. Once flashed, reconnect to view or change configuration.

In my case, I do the following:

• Change device name, as I have a few of these sensors, so I name them differently - "Set New Name"
• Tick "Comfort," "Show batt," and "Clock" to make the LCD display cycle through the different LCD screens.
• "Set Time" to set the device to the local machine time

I thought of monitoring these babies by running Home Assistant on my Raspberry Pi Zero W, but I seriously doubt the Pi has the grunt to make it work. Oh, well.