The Xiaomi Mijia model LYWSD03MMC is a thermometer and hygrometer with Bluetooth LE support.

Custom firmware[edit | edit source]

A custom firmware with additional features has been created by atc1441 and later improved by pvvx. You may flash the customized firmware over the air using Bluetooth and a modern web browser to take advantage of these additional features and improvements.

Visit pvvx's GitHub repo at https://github.com/pvvx/ATC_MiThermometer for more information.

To get started, visit https://pvvx.github.io/ATC_MiThermometer/TelinkMiFlasher.html and click on 'Connect'. Pair with your Mijia thermometer and assign a Bindkey. Click on 'Custom Firmware ver 3.8' and then upload it to the device.

Configuration[edit | edit source]

I configure my devices with the following:

  • Show measurement + battery
  • Advertising interval at 5000ms
  • Set a pin (to prevent someone from changing the settings)
  • Set comfort range to 18C - 26C and 30% - 60% RH

Home Assistant integration[edit | edit source]

After flashing the device with pvvx's custom firmware, my ESP32 running Open MQTT Gateway was able to seamlessly convert the device's Bluetooth advertisements to my MQTT server which Home Assistant was able to automatically discover. Basically, I didn't have to do anything for the sensors to show up with my existing infrastructure.

See also[edit | edit source]