110 lines
5.2 KiB
Markdown
110 lines
5.2 KiB
Markdown
# LYWSD03MMC 2025 B1.5 (HW B1.1) BTHome v2 beacon + LCD + OTA
|
|
|
|
Port of the nRF52840/Zephyr SHT41 beacon to the Xiaomi LYWSD03MMC
|
|
(Telink TLSR8251). Same behaviour:
|
|
|
|
- every 60 s: measure temperature/humidity, read the battery right after the
|
|
sensor load, update the advertisement
|
|
- BTHome v2 advertisement every 10 s, public (factory) address,
|
|
objects 0x0C voltage (mV), 0x2E humidity (%), 0x45 temperature (0.1 °C)
|
|
- name `LYWSD03MMC` in the advertisement and the scan response, so passive
|
|
scanners (ESPHome `active: false`) see it too (`ADV_NAME_IN_ADV 0` keeps
|
|
it in the scan response only, as pvvx does)
|
|
- a failed sensor read keeps advertising the last good T/RH; the voltage is
|
|
updated on every measurement
|
|
- Telink OTA service for over-the-air firmware updates, reachable only
|
|
during the first 2 minutes after the battery is inserted (see Flashing)
|
|
|
|
plus the display: temperature (0.1 °C, `°C`), humidity (`%`), battery icon
|
|
below 2.4 V, `-- --` until the first good reading. The LCD controller holds
|
|
the image itself and is only written when a value changes.
|
|
|
|
## Power saving (same methods as pvvx/ATC_MiThermometer)
|
|
|
|
- No wake-ups of its own: a measurement starts right after every 6th
|
|
advertising event, while the chip is awake anyway.
|
|
- The CPU sleeps during the ~12 ms sensor conversion (pvvx
|
|
`SENSOR_SLEEP_MEASURE`); an app wake-up timer collects the result.
|
|
- VDD is sampled while the sensor converts, i.e. under load.
|
|
- Deep-sleep retention between events, also while connected: the device
|
|
requests 20 ms interval / latency 49, so it wakes once per second.
|
|
- PB0 (battery probe) is driven high permanently; sensor I2C at 700 kHz;
|
|
RF power restored after every suspend.
|
|
- Battery protection: below 2.2 V at power-on, or below 2.0 V while running,
|
|
the LCD shows the voltage and `Lo` and the device deep-sleeps for 3 min
|
|
before any flash write or radio use, then retries.
|
|
|
|
Outside the 2-minute OTA window the advertising is non-connectable, as in
|
|
the original build: the radio does not listen after each packet.
|
|
|
|
## Hardware: 2025 "B1.5" only
|
|
|
|
This build supports **only the LYWSD03MMC sold since 2025 with "B1.5"
|
|
printed on the PCB** (next to the battery holder), whose LCD controller is
|
|
driven over bit-banged SPI. pvvx firmware / TelinkMiFlasher report this
|
|
board as **HW B1.1**, which is the reliable way to tell it apart.
|
|
|
|
| Board | Sensor | LCD controller |
|
|
|-------|--------------------|-----------------------------------|
|
|
| "B1.5" 2025 (pvvx B1.1) | SHTV3 (SHTC3) 0x70 | SPI, PD7 CLK / PB7 SDI, write-only |
|
|
|
|
There is no auto-detection. On any other unit (original UART-LCD B1.5,
|
|
B1.4, B1.6, B1.7, B1.9, B2.0) the display stays blank and/or the sensor read
|
|
fails: do not flash it there.
|
|
|
|
Pinout, segment map and the LCD frame format come from
|
|
pvvx/ATC_MiThermometer.
|
|
|
|
## Differences from the nRF build
|
|
|
|
- The sensor is wired straight to the coin cell, so there is no power gating;
|
|
the SHTV3 is put to sleep explicitly after every measurement.
|
|
- Voltage is VDD (= CR2032), measured by driving the unbonded PB0 pad high
|
|
and sampling it with the ADC. Uses the typical 1175 mV reference, so expect
|
|
a few % absolute error; adjust `ADC_VREF_MV` against a meter if needed.
|
|
|
|
## Build
|
|
|
|
```sh
|
|
git clone https://github.com/pvvx/ATC_MiThermometer ../ATC_MiThermometer
|
|
# TC32 toolchain (Linux): e.g. https://github.com/flyskywhy/tc32 branch "linux"
|
|
ln -s /path/to/tc32 ../ATC_MiThermometer/SDK/tools/linux/tc32
|
|
make
|
|
```
|
|
|
|
Produces `lywsd03mmc_b15_bthome.bin` (with the Telink CRC appended).
|
|
|
|
## Flashing
|
|
|
|
- **First install** (from stock Xiaomi or pvvx firmware, which have OTA):
|
|
https://pvvx.github.io/ATC_MiThermometer/TelinkMiFlasher.html → connect →
|
|
"Select Firmware" → custom file. Units running the previous build of this
|
|
firmware (no OTA) need one wired flash: USB-UART adapter on the SWS pad,
|
|
`TlsrComProg`/`ATCtelink.py` from the pvvx repo.
|
|
- **Updates** (this firmware → any Telink image ≤ 128 KiB, including back to
|
|
pvvx or stock), with https://pvvx.github.io/ATC_MiThermometer/TelinkOTA.html:
|
|
1. Take the battery out, wait ~5 s, put it back. The BLE symbol on the
|
|
LCD means the OTA window is open: for 2 minutes the device accepts
|
|
connections and advertises every second.
|
|
2. TelinkOTA.html → connect → pick `LYWSD03MMC` → select the `.bin` →
|
|
start. The upload must start within the 2 minutes; once started it may
|
|
run past them.
|
|
3. The device reboots into the new firmware. If the window closes or the
|
|
upload fails, start again from step 1.
|
|
|
|
All units are named `LYWSD03MMC`; only the unit you just power-cycled is
|
|
connectable, so it is the only one the page can connect to.
|
|
|
|
The new image is written to the inactive flash bank and only activated
|
|
after its CRC checks out, so an interrupted upload leaves the current
|
|
firmware running. The transfer aborts after 16 s without data.
|
|
|
|
The window opens only on a real power cycle. Reboots without one
|
|
(low-battery sleep, OTA reboot, crash) keep it closed. After installing
|
|
this firmware by OTA from pvvx firmware, power-cycle once before the next
|
|
update.
|
|
|
|
**OTA itself is unauthenticated**: anyone in Bluetooth range can upload
|
|
firmware while the window is open, so it is limited to 2 minutes after a
|
|
battery swap, which needs physical access.
|