NEW B1.6 (with RX pin connected) is not supported - Hardware B1.6 - blank LCD

[deveon95]

I've flashed this unit using the UART method.

The flashing was successful and it was seen by Zigbee2MQTT but the screen is blank. Toggling the screen on setting doesn't turn it on,

Per the instruction "If you flashed the module but the screen is remaining blank, try python3 TLSR825xComFlasher.py -p <YOUR_COM_PORT> ea to erase all flash and then write the firmware again", I erased the flash and programmed it again but the screen remains blank.

By "blank", I mean the screen looked like its powered but with all the segments off, because all the segments look faint if held at an angle. The segments don't ever turn on, not even during power-up.

Is this hardware revision supported by the firmware?

[devbis]

All know revisions are supported including this one. It has the same schematics as B1.5.
Try to erase and upload more times, as UART dongle/script is just an emulator for the SWS protocol that is used.

[288GTO]

Same issue here.

I just received 3 units of the LYWSD03MMC / Xiaomi Thermometer / Hygrometer from AliExpress.
The hardware version on the board exactly matches the photos shared earlier in this thread.

I’ve flashed multiple firmware versions - starting with ATC_ota_40000.bin, then updating OTA to the latest z03mmc.bin (3001-1100 / 2024-02-04).

On all devices, the LCD was effectively blank - only extremely faint digits were visible if viewed at a certain angle.
However, they were fully functional in Home Assistant via Zigbee2MQTT (Z2M).

Just now, I flashed this alternative custom firmware using UART, and the LCD is now working as expected.
The device is fully recognized and operational in HA/Z2M.

I know this is a different project from what’s being discussed here, but in my case, it works.

From what I’ve read here, the LCD matrix and controller can vary between hardware revisions - maybe that’s why the display stays blank on HW:B1.6?

[deveon95]

I've flashed Z03MMC_v0129.bin on mine and it is now working as well.

I noticed that the screen doesn't always come on after inserting the battery with pvvx's Z03MMC_v0129.bin, which makes me wonder if it's a startup timing issue. The UART programming is very flakey, and I'm not sure how many times I can get away with soldering the pads before they rip off anyway, so I'm going to leave that unit alone now since pvvx's firmware has all the features I need.

Maybe the screen with come on with devbis's firmware if I reinsert the battery enough times or reset it with the reset pin on the microcontroller (not the same thing as the reset pad next to the battery), but obviously I can't test that now without reprogramming it again. I might try devbis's firmware again if I get another unit in the future.

[francescovannini]

Same identical problem; I've flashed pvvx firmware but I'm not satisfied with temperature sensitivity and reporting frequency (which is much lower than this firmware). Any chances we can get the devbis to work on hardware 1.6? It's indeed strange that it doesn't because code definitely accounts for 1.6, like here:

z03mmc/src/lcd.c

Line 73 in 377a10b

}else{// B1.6 uses UART and is not testable this way

I very quickly compared the two firmware and noticed this difference:

z03mmc/src/lcd.c

Line 108 in 377a10b

drv_uart_pin_set(UART_TX_PD7, UART_RX_PB0);

here TX is on PD7 and RX on PB0

but on pvvx

https://github.com/pvvx/ZigbeeTLc/blob/3f11d853ab90cd69e4ceb41dc9ed9fdfbb43a2e5/src/lcd_lywsd03mmc.c#L168

TX is on PD7 as before, BUT RX seems to be on PB7.

Might be that just the comments or the var names are wrong, I did not check the actual values.

[devbis]

For this display only TX is used. So we can use any RX pin that is not connected and is available for RX function.

typedef enum{
	UART_RX_PA0 = GPIO_PA0,
	UART_RX_PB0 = GPIO_PB0,
	UART_RX_PB7 = GPIO_PB7,
	UART_RX_PC3 = GPIO_PC3,
	UART_RX_PC5 = GPIO_PC5,
	UART_RX_PD6 = GPIO_PD6,
}UART_RxPinDef;

But some of them are connected on the board, we need to use a free one. AFAIK both pins are not connected.

[francescovannini]

Did some digging:

• There seems to be confusion on B1.6; multiple hardware versions all tagged with B1.6 are actually different hardware.
• This led to a recent update on pvvx firmware
• I believe the solution might be in this commit. Please have a look at the diff of src/board_lyws03mmc.h and src/lcd_lywsd03mmc.c (very bottom of the page).

#define GPIO_LCD_URX 		UART_TX_PD7  // UART RX LCD old B1.6
#define GPIO_LCD_CLK 		GPIO_PD7  	 // SPI-CLK LCD new B1.6
#define GPIO_LCD_UTX 		UART_RX_PB7  // UART TX LCD old B1.6
#define GPIO_LCD_SDI 		GPIO_PB7  	 // SPI-SDI LCD new B1.6

Any chances you can attempt the same changes on your firmware?

Here some mapping I did on my hardware (it matches the one in the first comment above and the new code).

[aka13-404]

There is also a similar version to the 1.6, where it's seemingly 1.5 branded board, but actually 1.6 hw. (pvvx/ATC_MiThermometer#747)

I just received a couple of those (makes me sad, I was so happy for a mass-made cheap always available sensor being available).
Not sure if I can provide any meaningful input in addition to what @francescovannini already posted.

Copy of my pictures I provided in the other issue, so that it's all in one place here as well:

[pvvx]

HW versions LYWSD03MMC

HW	LCD I2C addr	SHTxxx I2C addr	Note
B1.4	0x3C	0x70 (SHTC3)
B1.5	UART	0x70 (SHTC3)
B1.6	UART	0x44 (SHT4x)
B1.7	0x3C	0x44 (SHT4x)
B1.9	0x3E	0x44 (SHT4x)
B2.0	0x3C	0x44 (SHT4x)
PCB Mark: B1.6* (2025)	SPI	0x4x (SHT4x/GXHT40/other clones...)	not supported
PCB Mark: B1.5* (2025)	SPI	0x7x (SHTC3/GXHTC3/other clones...)	not supported

• "PCB Mark: B1.6/B1.5" are new variants that went on sale in 2025.
  These devices use old printed circuit boards from warehouses. They are equipped with clones of cheaper sensors and an SPI-controlled LCD controller. Moreover, a large number of defective LYWSD03MMC units have already been reported for sale, mostly with faulty LCD chips.