Xiaomi Air Purifier 3H Reverse Engineering Part 1: Probing Around

Welcome to the family Xiaomi Air Purifier H3!

If something enters my house I open it as quickly as possible and start probing around.

The following information is for educational Purposes only!
Note, I absolutely love Xiaomi stuff since it is cheap, of decent build quality, and it’s fun to probe around in!

How to disassemble the device:

The device itself is quite easy to disassemble. One of the first things that is noticeable is that a bare minimum of screws that are used. The bottom side has four, and underneath the bottom plate has another four screwed in. Almost the complete assembly is made to click-clack-badabing-badaboom and your done (my way of putting things together). Seldom I see products this well constructed with mass production in mind. The engineers at Xioami absolutely did a great job! For every product engineer on this planet: buy this device, take it apart, and learn from it!

When opening the device we find the following main board:

AC-M6-B01

REV3-BDR

XIaomi Air FIlter H3 Main Board Pinout Pins
Connector _pins:
Function
J1
ESP_PROG_HEADER
-1
3V3
-2
GND
-3
ESP-32-UART0-TX
-4
ESP-32-UART0-RX
J2
STM_SERIAL_DEBUG
-1
STM32-RX
-2
STM32-TX
-3
GND
-4
3V3
J3
ESP_GPIO_0_HEADER
-1
ESP-32-GPIO-0
-2
GND
J4
MOTOR_CONNECTOR
-1
24V
-2
GND
-3
5V
-4
PWM
-5
BRK?
-6
?
-7
FG?
J7
PLANT_POWER_CONNECTOR
-1
?
-2
?
-3
?
-4
RX
-5
TX
-6
SET
-7
GND
-8
5V
J8
POWER_CONNECTOR
-1
24V
-2
GND
J9
STM_PROGRAMMING_HEADER
-1
3V3
-2
GND
-3
SWDIO
-4
CLK
-5
SWO
-6
NC?
J10
NFC_HEADER
-1
SDA
-2
3V3
-3
STATE
-4
GND
-5
SCL
J11
SHT_20+BUTTON_HEADER
-1
SCL
-2
GND
-3
LED_ON
-4
3V3
-5
SDA
-6
? (button?)
J12
DOOR_SWITCH
-1
BOT_DOOR
-2
GND

J6 is the header that is used for the OLED display. I could not be bothered to probe it as I’m not trying to hack the display.

IC’s used:

Designator IC
U3 Fremont   FT24C64A
U4 Espressif ESP-WROOM-32D
U5 ST STM32F412RET6

U3 = an 64K EEPROM datasheet: Click

U4 = an Espressif wifi adapter. This IC/ Package handles all the WIFI/BLE Traffic.

U5= The main Microcontroller.

This is a good start for reverse engineering. No mysterious Chinese crap IC’s. In the following parts of this series of blog posts we will look into the contents of these chips 😀

More info on this project will be added on the project’s Github page.

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