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Xiaomi Mijia (LYWSD03MMC) & Xiaomi Miaomiaoce (MHO-C401) & CGG1 Mijia Bluetooth Thermometer Firmware

This repository contains custom firmware for two Xiaomi Mijia Smart Bluetooth Thermometer & Hygrometer devices.

The custom firmware can be flashed via a modern browser and over-the-air (OTA) without opening the device and unlocks several customization options. You can go back to the original firmware at any time.

Key features

  • Supports connections using PIN-code and encrypted bindkey beacon.
  • 3 LCD Display Screens (Looping): Temperature & Humidity & Comfort, Temperature & Battery Level, Clock
  • Measurement values recording & Charting. See Reading Measurements from Flash
  • Adjustable correction offsets and Comfort zones
  • Improved battery life
  • Concurrent support for Xiaomi, ATC and Custom Bluetooth Advertisement format
  • Adjustable RF TX Power & Bluetooth advertising interval
Xiaomi Mijia (LYWSD03MMC) Xiaomi Miaomiaoce (MHO-C401) Qingping Temp & RH Monitor (CGG1-Mijia)
Xiaomi Mijia (LYWSD03MMC) Xiaomi Miaomiaoce (MHO-C401) E-ink CGG1 'Qingping Temp & RH Monitor', Xiaomi Mijia DevID: 0x0B48

Table of content

Getting Started

You can conveniently flash, update and configure the bluetooth thermometers remotely using a bluetooth connection and a modern web browser.

Flashing or Updating the Firmware (OTA)

To flash or update the firmware, use a Google Chrome, Microsoft Edge or Opera Browser.

  1. Go to the Over-the-air Webupdater Page TelinkMiFlasher.html *
  2. If using Linux: Ensure you enabled "experimental web platform features". Therefore copy the according link (i.e. chrome://flags/#enable-experimental-web-platform-features for Chrome), open a new browser tab, paste the copied URL. Now sten the Experimental Web Platform features flag to Enabled. Then restart the browser.
  3. In the Telink Flasher Page: Press Connect: The browser should open a popup with visible Bluetooth devices. Choose the according target device (i.e. LYWSD03MMC) to pair.
  4. After connection is established a Do Acivation button appears. Press this button to start the decryption key process.
  5. Now you can press the Custom Firmware ver x.x button to directly flash the custom firmware. Alternatively you can choose a specific firmware binary (i.e. the original firmware) via the file chooser
  6. Press Start Flashing.
  • Use TelinkOTA to flash old or alternative versions (ATC1441). This is a program for OTA projects with Telink SDK, no third-party (mijia) protections.


After you have flashed the firmware, the device has changed it's bluetooth name to something like ATC_F02AED. Using the TelinkMiFlasher.html you have various configuration options.

General process:

  1. Press Connect
  2. Select the according device to connect/pair (i.e. ATC_F02AED)
  3. Several configuration options appear
  4. Choose Send Config to send changed value to the device. Or press Set default and then Send config to revert to the Defaults
Option Description
Temperature and Humidity offset Enter a value to correct the offset of the Temperature or Humidity displayed: For example -1.4 will decrease the Temperature by 1.4°
Smiley or Comfort Choose a static smiley or check the "Comfort" Radio box to change the smiley depending on current Temperature and Humidity.
Comfort Parameters Defines the Lower (Lo) and Upper (Hi) Range for Temperature and Humidity interpreted as comfort zone. In the default configuration a smiley will appear.
Advertising Type Type of supported Bluetooth Advertising Formats. By default all formats are enabled.
Set time sends the current time to the device
Comfort, Show batt, Clock Ticking the according boxes you can enable interval rotation between different LCD screens. See the example video below.

Example of LCD display modes

You can configure different LCD Display modes using Comfort, Show batt and Clock configuration checkboxes. The enabled LCD Display Modes will appear one-by-one in a loop.


Battery and clock display are enabled in the settings. The rest of the settings is kept default. The video contains 2 cycles.

  1. Temperature and humidity
  2. Temperature and % of battery
  3. Temperature and humidity
  4. Hours and minutes


Firmware Binaries

You can directly update/flash the firmware without downloading the binaries below.

Custom Firmware Versions:

Original Manufacturer Firmware Version

In case you want to go back to the original firmware, you can download them here:

Firmware version history

Version Changes
1.2 Bind, Set Pin-code, Support MHO-C401
1.3 Get/Set comfort parameters
1.4 Get/Set device name, Get/Set MAC
1.5 Add Standard Device Information Characteristics
1.6 Fix alternation of Advertising in mi mode
1.7 Authorization and encryption in permissions to access GAP ATT attributes, if pin code is enabled
1.8 Time display (instead of a blinking smile)
1.9 Recording measurements to flash memory (cyclic buffer for 19632 measurements)
2.0 Recording measurements with averaging to flash memory
2.1 Periodic display refresh for MHO-C401
'Erase mi-keys' option to return to original firmware
2.2 Added parameter "Encrypted Mi Beacon"
2.3 Added "Delete all records"
2.4 Added parameter "Clock time step"
2.5 Remove TRG/FLG errors, minor optimization
2.6 Expanding the ranges of threshold parameters (TRG)
2.7 Reducing power consumption of MHO-C401 (EDP update), adding version for CGG1
2.8 Added saving bindkey to EEP if mi-keys are erased, reduced TX power to 0 dB for defaults
2.9 Added additional id flags to advertising packages
3.0 Added toggle support for advertising package structures for third-party software
3.1 Fix security attributes for pincode


Reading Measurements from Flash



Reading Measurements in Connected Mode

GraphAtc.html GraphAtc1.html GraphAtc2.html DevPoint.html


Reading Measurements in Advertising Mode

This requires the Experimental Web Platform Features flag enabled in your browser. See Flashing or Updating the Firmware (OTA).


Technical specifications

Average power consumption

Xiaomi Mijia (LYWSD03MMC)

Using the default settings for advertising interval of 2.5 seconds and measurement interval of 10 seconds:

  • Bluetooth Advertisement: 15..20 uA 3.3V (CR2032 over 6 months)
  • Bluetooth Connection: 14..25 uA 3.3V (CR2032 over 6 months)

Xiaomi Miaomiaoce (MHO-C401)

Using the default settings for advertising interval of 2.5 seconds and measurement interval of 20 seconds:

Bluetooth Advertising Formats

The Firmware can be configured to support one of four different Bluetooth advertisements data formats. Supports bindkey beacon encryption.

You can also configure to transferring everything in turn (round-robin)

atc1441 format

UUID 0x181A - size 16: atc1441 format

Custom format (all data little-endian):

UUID 0x181A - size 19: Custom format (all data little-endian):

uint8_t     size;   // = 19
uint8_t     uid;    // = 0x16, 16-bit UUID
uint16_t    UUID;   // = 0x181A, GATT Service 0x181A Environmental Sensing
uint8_t     MAC[6]; // [0] - lo, .. [6] - hi digits
int16_t     temperature;    // x 0.01 degree
uint16_t    humidity;       // x 0.01 %
uint16_t    battery_mv;     // mV
uint8_t     battery_level;  // 0..100 %
uint8_t     counter;        // measurement count
uint8_t     flags;  // GPIO_TRG pin (marking "reset" on circuit board) flags: 
                    // bit0: GPIO_TRG pin input value (real level)
                    // bit1: GPIO_TRG pin output value (pull Up/Down)
                    // bit2: Output GPIO_TRG pin is controlled according to the set parameters
                    // bit3: Temperature trigger event
                    // bit4: Humidity trigger event

Xiaomi Battery Charge

  1. UUID 0xFE95 - 0x0A: Xiaomi - battery charge level 0..100%, battery voltage in mV

Xiaomi Temperature & Humidity

  1. UUID 0xFE95 - 0x0D: Xiaomi - temperature x0.1C, humidity x0.1%

Xiaomi Encrypted (bindkey enable)

  1. UUID 0xFE95 - 0x0A, 0x04, 0x06 Xiaomi - battery charge level 0..100%, temperature x0.1C, humidity x0.1% (All data are averaged over a period of 16 measurements)

Bluetooth Connection Mode

  • Primary Service - Environmental Sensing Service (0x181A):
  • Characteristic UUID 0x2A1F - Notify temperature x0.1C
  • Characteristic UUID 0x2A6E - Notify temperature x0.01C
  • Characteristic UUID 0x2A6F - Notify about humidity x0.01%
  • Primary Service - Battery Service (0x180F):
  • Characteristic UUID 0x2A19 - Notify the battery charge level 0..99%
  • Primary Service (0x1F10):
  • Characteristic UUID 0x1F1F - Notify, frame id 0x33 (configuring or making a request): temperature x0.01C, humidity x0.01%, battery charge level 0..100%, battery voltage in mV, GPIO-pin flags and triggers.

Temperature or humidity trigger on GPIO PA5 (label on the "reset" pin)




  • =0 off,
  • if less than zero - activation on decrease,
  • if more than zero - activation on excess

Setting the pin to "1" or "0" works if both hysteresis are set to zero (TRG off).


Interface for receiving and displaying data on the LCD.

  • LCD shows:
  • Big number: -99.5..1999.5
  • Small number: -9..99
  • Smiley, battery, degrees
  • Setting the display time limit in sec


The USB-COM adapter writes the firmware in explorer. Web version.

  • Connect only TX-SWS and GND wires.




  • TLSR8251F512ET24 (TLSR8258 in 24-pin TQFN). SoC: TC32 32-bit MCU 48Mhz, 64 KiB SRAM, 512 KiB Flash (GD25LE40C), Bluetooth 5.0: Mesh, 6LoWPAN, Zigbee, RF4CE, HomeKit, Long Range, Operating temperature: -40°C to +85°C, Power supply: 1.8V to 3.6V.
  • SHTV3 sensor. Measurement range: Temperature -40°C to +125°C, Humidity 0 to 100 %RH. Power supply: 1.8V to 3.6V
  • IST3055NA0 LCD controller

LYWSD03MMC BoardPinout


Building the firmware

  1. Go to and get the IDE for TLSR8 Chips.
  2. Clone
  3. Install the IDE and import the 'ATC_MiThermometer' project
  4. Change 'Linked resource' and 'C/C++ Build/Build command'.
  5. Compile the project

Related Work

ATC_MiThermometer is based on the original work of @atc1441, who developed the initial custom firmware version and the web-based OTA flasher (Source).

Resources & Links

CJMCU-2557 BQ25570


Control function ID when connected

Primary Service UUID 0x1F10, Characteristic UUID 0x1F1F

ID Command
0x01 Get/Set device name
0x10 Get/Set MAC
0x11 Get/Set Mi key: DevNameID
0x12 Get/Set Mi keys: Token & Bind
0x15 Get all Mi keys
0x16 Restore prev mi token & bindkeys
0x17 Delete all Mi keys
0x18 Get/set binkey in EEP
0x20 Get/Set comfort parameters
0x22 Get/Set show LCD
0x23 Get/Set Time
0x24 Get/set adjust time clock delta
0x33 Start/Stop notify measures in connection mode
0x35 Read memory measures
0x36 Clear memory measures
0x44 Get/Set TRG config
0x45 Set TRG output pin
0x4A Get/Set TRG data (not save to Flash)
0x55 Get/Set device config
0x56 Set default device config
0x5A Get/Set device config (not save to Flash)
0x60 Get/Set LCD buffer
0x61 Start/Stop notify LCD buffer
0x70 Set PinCode
0x71 Request Mtu Size Exchange