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Home Assistant room temperature and humidity with Bluetooth thermometer and ESPHome

Bluetooth LE temperature sensor and ESP32 microcontroller

This is one of the easiest ESPHome projects to build with no tools or soldering required. This guide explains how to integrate room temperature in Home Assistant using a low cost ($5 USD) Bluetooth Low Energy (BLE) thermometer with a Bluetooth LE gateway using a low cost ($5 USD) ESP32 microcontroller running ESPHome software.

Home Assistant dashboard with temperature and humidity

Overview

If some rooms of your home feels warmer or colder than other rooms, then it might be useful to use a thermometer to measure and collect temperature and humidity data in specific rooms so you can make adjustments to improve home comfort. Home Assistant logs data history for any sensor and the dashboard displays a chart of historical measurements. With the Xiaomi Mijia Bluetooth thermometer, you can place the thermometer on a wall in your home without it looking out of place in a home. By using multiple thermometers in different rooms, you can compare temperature and humidity of different rooms in your home.

Home Assistant dashboard with temperature history

Prerequisites

Hardware required

Software required

Tools required

  • No special tools needed, nothing to take apart or assemble.

LYWSD03MMC Xiaomi Mijia Bluetooth thermometer

Xiaomi Mijia Bluetooth thermometer (model LYWSD03MMC) is a small smart thermometer about the size of a 9V battery.

  • Has a built-in 1.5in LCD display that shows current temperature and humidity
  • Displays temperature in Celsius, but can display in Fahrenheit with custom firmware
  • With its white case, it can be easily mounted on a wall with included sticky pad and blends into the background without looking out of place.
  • Powered by a replaceable CR2032 coin cell battery
  • Has integrated Bluetooth Low Energy (BLE) wireless connectivity that will be used to integrate this sensor with Home Assistant
  • Can be used with Home Assistant without pairing with Mijia smart home app
  • Powered by Telink TLSR82xx series ultra low power microcontroller designed for Internet of Things (IoT)

ESP32 SoC microcontroller

ESP32 is a microcontroller that uses a System on Chip (SoC) processor that provides a lot of capability at a low price and small size. For about $5 USD, the SoC has integrated 802.11 b/g/n Wi-Fi and Bluetooth v4.2 connectivity. It's size is slightly larger than a SD card. Programs can be transferred to the onboard flash memory through micro USB cable connected to your PC or wirelessly through Wi-Fi. Device can be powered by USB cable or directly by a 5V DC power source.

Comparison to Arduino

Both ESP32 and Arduinos run a single program rather than an operating system. ESP32 single board computer (SBC) is much faster and has more connectivity than the similarly sized Arduino Nano microcontroller. ESP32 has 100x RAM and 10x flash memory of the Arduino Nano. Arduino Nano does not have Wi-Fi or Bluetooth. Both devices can be powered by USB cable or directly by a 5V DC power source.

Comparison to Raspberry Pi

Raspberry Pi uses faster ARM SoC processor. Even the slower Raspberry Pi Zero is much more powerful (has 1000x more RAM than ESP32) and runs a full Linux operating system at a higher cost, and uses micro SD card for storage. Both Raspberry Pi Zero W and ESP32 support 802.11 b/g/n Wi-Fi and Bluetooth. Both devices can be powered by USB cable or directly by a 5V DC power source.

Home Assistant Bluetooth LE sensor gateway

The ESP32 microcontroller can be configured to act as a Bluetooth sensor gateway, detecting broadcasts from Bluetooth Low Energy sensors and transmitting the events to Home Assistant over Wi-Fi network. With ESP32 microcontroller's built-in Bluetooth and Wi-Fi connectivity, you don't need Bluetooth on the PC or device Home Assistant is installed on. Bluetooth Low Energy sensors broadcasts data on a periodic basis. To prolong the sensor battery life, the ESP32 microcontroller doesn't "pair" or maintain active connection with each sensor.

Instructions

Building this is separated into 3 phases

  1. Flash Bluetooth thermometer with custom firmware
  2. Update ESPHome configuration to detect Bluetooth thermometer
  3. Configure Home Assistant integration for sensors in the Bluetooth thermometer

Before proceeding, you'll need Home Assistant already installed and running on a device like a Raspberry Pi. See Prerequisites section for more details.

Step 1: Flash Bluetooth thermometer with custom firmware

To unlock additional customization options like displaying temperature in Fahrenheit units and to broadcast unencrypted sensor data, it's recommended to flash custom open source firmware on the model LYWSD03MMC Xiaomi Mijia Bluetooth thermometer. The device can be flashed wirelessly Over The Air (OTA) using a web browser on a PC with Bluetooth.

  1. Follow the steps for flashing custom firmware described on Instructions for flashing or updating firmware. GitHub contributors pvvx, atc1441, and others have done a great job developing the browser flashing tool and documenting the instructions.
    • Firmware is transferred wirelessly through Bluetooth connection. For best results, make sure the Bluetooth thermostat is close (within 1ft) from PC with browser you're flashing from. Telink Flasher Start Flashing button
  2. After custom firmware is successfully transferred, follow the steps for changing configuration described in configuration section as needed. Suggested changes are:
  3. Change the LCD to display Fahrenheit units. (Temperature setting, then select "Send Config" button)
  4. Disable recording average measurments to internal flash memory to prolong the flash memory lifespan (set "Recording averaging measures to flash memory" to 0)
  5. Rename the device to indicate room device will be placed in (Enter new device name, then select Set New Name button)
  6. When you're finished making changes, verify you've selected Send Config, then select Disconnect button. Telink Flasher device configuration options

Step 2: Update ESPHome configuration to detect Bluetooth thermometer

Now that your Xiaomi Mijia Bluetooth thermometer is running custom firmware and broadcasting unencrypted temperature data, the next step is to load ESPHome software on your ESP32 microcontroller and configure it to listen to temperature and humidity data broadcasted by your Bluetooth thermometer, and then re-trasnmit that data to Home Assistant.

  1. In Home Assistant, install ESPHome Dasbhoard add-on by following the instructions at ESPHome Getting Started guide
  2. Within ESPHome Dashboard, select green + New Device button and enter your desired device name. The device name is visible in Home Assistant Integrations page, but won't be visible on Home Assistant dashboards.
  3. Select ESP32 device if using ESP32
  4. Cancel install at this time, as we'll modify the configuration file first.
  5. Select Edit button to edit the ESPHome *.yaml configuration file
  6. Edit Wi-Fi network SSID and password. As a security best practice, hide the passwords in secrets.yaml file.
  7. Add esp32_ble_tracker: to the bottom of the .yaml config like below
esp32_ble_tracker:
  1. Select Save, then select Install. Choose your preferred install method. Manual download is the easiest method for the initial flashing. Wireless install is easiest flash option after ESP32 device is connected to your wireless network.
  • If using Manual download, then download the compiled program (*.bin file) from ESPHome Dashboard, connect ESP32 device to your PC using USB cable, and then use ESPHome Web software to flash the *.bin program to your ESP32 device.
  1. After ESP32 is flashed successfully with new configuration, view logs to determine the MAC address (ex: A1:B1:C1:D1:E1:F1) of your Xiaomi Mijia Bluetooth thermometer. The ESPHome Web utility automatically displays logs after flashing, or you can use ESPHome Dashboard and select "Logs" if your ESP32 was successfully connected to your local Wi-Fi network. Logs will show the MAC address and name of the detected Bluetooth Low Energy devices. ESPHome Flasher displays ESP32 logs
  2. Within the ESPHome Dashboard, select "Edit" button to edit the ESPHome *.yaml configuration. Use my sample ESPHome configuration.yaml as a reference and add the following to the bottom of the .yaml config. Update mac_address with the MAC address you determined in the previous step.
esp32_ble_tracker:

sensor:
  - platform: pvvx_mithermometer # LYWSD03MMC Mijia Therometer
    mac_address: "A1:B1:C1:D1:E1:F1" # LYWSD03MMC MAC address
    temperature:
      name: "T1 Temperature"
    humidity:
      name: "T1 Humidity"
    battery_level:
      name: "T1 Thermometer Battery Level"
    battery_voltage:
      name: "T1 Thermometer Battery Volts"

# Auto daily reset
time:
  - platform: homeassistant
    on_time:
      - seconds: 0
        minutes: 0
        hours: 4
        days_of_week: MON-SUN
        then:
           - switch.toggle: restart_switch
switch:
  - platform: restart
    name: "ESP-BLE-TEMP restart"
    id: restart_switch
  1. Select Save, then select Install. Your ESP32 should have successfully connected to your Wi-Fi network and should be detected as online in ESPHome Dashboard at this point, so Wirelessly is the easiest option. If your ESP32 is not detected as online in ESPHome Dashboard, then double check you've configured the correct Wi-Fi SSID and password in your configuration yaml.

Step 3: Configure Home Assistant integration for sensors in the Bluetooth thermometer

After configuring ESP32 to detect temperature and humidity broadcasted by your Bluetooth thermometer and re-transmit that as a Home Assistant sensor, the last step is to enable ESPHome integration so that ESPHome dashboard displays temperature and humidity data.

  1. In Home Assistant, navigate to Integration page under Configuration -> Devices & Services.
  2. ESPHome should automatically appear as a discovered integration. If not, follow ESPHome instructions to manually add ESPHome integration.
  3. Select Configure button, and set the area of the device. Home Assistant Overview dashboard groups temperature, humidity and other sensors & switches per area by default.
  4. Check Home Assistant Overview dashboard and look for the "T1 Temperature" and "T1 Humidity" sensors.

Conclusion

Congratulations! Now you can view and log temperature and humidity in Home Assistant using Xiaomi Mijia Bluetooth thermometer (model LYWSD03MMC). With the low cost of LYWSD03MMC Bluetooth thermometer, you can buy a few and place them in each area of your home. A single ESP32 microcontroller can detect data broadcast from multiple Bluetooth thermometers.