Connecting Xiaomi Mijia Bluetooth Hygrothermograph 2 to your phone: full error analysis instructions

Xiaomi Mijia Bluetooth Hygrothermograph 2 (LYWSD03MMC) is a compact device for monitoring temperature, humidity and atmospheric pressure in the room. Unlike the first version, the 2nd generation model supports Bluetooth 5.0, which provides more stable connection and lower battery consumption. However, many users face difficulties when connecting to a smartphone for the first time — especially if we are talking about phones on Android 12+ or iOS 15+, where the rules of working with Bluetooth-lean devices have changed.

In this article, we will look at all the stages of connection, from preparing the phone to setting up notifications in Mi Home. Particular attention will be paid to common errors (for example, when the device is not located or is displayed as “unknown”), as well as the nuances of working with alternative firmware (such as ATC1441 or PVVX>), which extend the functionality of the weather station. If you want to not only connect the gadget, but also learn how to calibrate its readings or integrate with Home Assistant, here you will find answers.

Before you go to the instructions, check what you have:

1. Preparation of the telephone and weather station for connection

Before connecting first, make sure your smartphone meets the minimum requirements. Xiaomi Mijia Hygrothermograph 2 weather station officially supports:

• 📱 Android 6.0 and higher (but on version 12)+ Additional permissions may be required)
• 🍎 iOS 10.0 and higher on iPhone 6s newer)
• 🔄 Bluetooth 4.2+ (5.0 recommended for stable operation)
• 📶 Internet connection (only for first setup in Mi Home)

Also check that the device has the latest version of the Mi Home app, which can be downloaded officially:

• 🤖 Google Play for Android)
• 🍎 App Store (for iOS)

If you are using a Chinese version of a weather station (with the inscription LYWSD03MMC without the letter B at the end), you may need to change the region in Mi Home to China.

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If you have a custom firmware phone (like LineageOS), turn on Bluetooth compatibility mode in the developer settings before connecting (Settings → System → For developers → Disable Bluetooth A2DP Hardware Offload).

2. Step-by-step instructions for connecting via Mi Home

Follow this algorithm to add a weather station to the app:

1. Turn on Bluetooth on your phone and make sure the weather station is nearby (no further than 1 meter).
2. Start Mi Home and log in (if you haven’t already).
3. Click + → Add the device in the upper right corner.
4. In the search box, type Mijia Bluetooth Temperature and Humidity Sensor 2 or select Sensors → Temperature and Humidity.
5. Click on the device found and wait until the application starts searching.
6. When the weather station appears in the list, click on it and confirm the connection.

If the device is not located, try:

• 🔄 Change the region in Mi Home to China (if you have a Chinese version of the sensor).

Once successfully connected, the weather station will appear in the Mi Home main menu with current temperature and humidity, but for full operation, we recommend you to perform additional settings, which we will discuss later.

Adjustment of notifications and calibration of readings

By default, the Xiaomi Mijia 2 weather station sends data to Mi Home every 10 minutes, but this interval can be changed.

1. Open the device card in Mi Home.
2. Press on. ⚙️ Settings → Update interval.
3. Choose the right option: 5 minutes, 10 minutes or 30 minutes.

To set up critical notifications (e.g. if the temperature exceeds 30°C or humidity drops below 40%):

1. Go to Settings. → Notifications.
2. Activate the Temperature/Humidity Notice slider.
3. Set thresholds and save settings.

If the weather station readings are inaccurate (for example, humidity is inflated by 5-10%), you can perform a calibration.

• 📏 Compare the data with another proven hygrometer (e.g. Xiaomi Mijia 1 or mechanical appliance).
• 🔧 At Mi Home, go to Settings → Sizing and corrections.
• ⚠️ Do not calibrate the device in the first 24 hours after installation – sensors need time to adapt to the environment.

4. Common mistakes and their solutions

Even with the right connection, users face problems.

If the weather station connects, but after a few hours falls off, check:

• 🔋 Battery charge – when the charge is below 20%, the connection becomes unstable.
• 📵 Interference from other devices – 2.4GHz Wi-Fi routers can create noise.
• 🔄 Background optimization in Android – add Mi Home to exceptions (Settings) → Annexes → Mi Home → Battery → No restrictions).

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If the weather station periodically shuts down, try reflashing it to an alternative firmware (e.g., PVVX), which solves the communication breakdown problem on 90% of devices.

5. Alternative firmware: why they are needed and how to install

The standard firmware from Xiaomi has limitations:

• 🔒 No data export to Home Assistant or other smart home systems.
• ⏱ Data update interval fixed (minimum 5 minutes).
• 📊 No pressure calibration (temperature and humidity only).

Alternative firmware (e.g. ATC1441, PVVX or Custom Firmware by pvx) extends the functionality of:

• ⚡ Update data every 10 seconds (instead of 5 minutes).
• 🔄 Support MQTT Integration with Home Assistant.
• 📈 Accurate calibration of all sensors, including pressure.
• 🔋 Optimized energy consumption (battery lasts up to 2 years).

To create a weather station, you will need:

1. A USB-TTL adapter (e.g., CP2102 or FT232RL)
2. Flash Tool (e.g. nrf52-flasher for Windows/Linux)
3. Firmware (you can download it on GitHub pvx).

Attention! Firmware via USB-TTL requires soldering and can lead to loss of warranty. If you are not sure about your skills, you should consult a specialist.

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For firmware without soldering, you can use the wireless method through the MiThermometer app (available for Android), but it does not work on all versions of sensors.

6.Integration with Home Assistant and other smart home systems

If you use Home Assistant, you can connect the weather station in two ways:

1. Mi Home Integration (official method):
2. Through MQTT (if custom firmware is installed):

Other systems (such as OpenHAB or Domoticz) require:

• 🔌 Set up MQTT-broker (e.g. Mosquitto).
• 📡 Use a plugin for Xiaomi (if supported).
• 🔄 Update the weather station to the version with support MQTT.

If you don't want to mess around with firmware, you can use a cloud bridge over Mi Home and IFTTT, for example, set the humidifier to automatically turn on when the humidity drops below 40%.

1. Create an applet in IFTTT with the Xiaomi Hygrothermometer → Humidity below 40% trigger.
2. Add the Turn on humidifier action (if your humidifier is supported).

7. Optimization of operation and extension of battery life

The standard CR2032 battery lasts 6-12 months depending on the frequency of updates.

• ⏱ Set the 30 minute refresh interval (unless you need frequent data).
• 📵 Turn off notifications if they are not critical.
• 🔋 Use premium batteries (e.g. Duracell or Energizer).
• 🌡 Place the sensor away from heat sources (such as batteries or direct sun).

Important: if the weather station stopped sending data, but the indicator flashes when you press a button, the problem is the battery, even if it seems charged. Replace it with a new one.

To check the level of charge:

1. Open the device card in Mi Home.
2. Click on the icon. ⚙️ Settings → Battery status.
3. If the level is below 20%, replace the battery.

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To avoid losing your battery history, bring your phone with the Mi Home open to the weather station before removing the old battery, which will save the latest readings.

FAQ: Frequent questions about Xiaomi Mijia Hygrothermograph 2