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

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