[BK7231N ] Teardown of TH08 LCD Calendar/clock/temperature/humidity, 3xAAA battery, backlight

morgan_flint 31497 241

#241 21625858 04 Aug 2025 18:05

divadiow divadiow

Level 35

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Post #241
21625858 04 Aug 2025 18:05

still only those IDs

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#242 21626813 05 Aug 2025 19:47

bogdanelhh bogdanelhh

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Post #242
21626813 05 Aug 2025 19:47

It seems that after recharging the batteries stopped working and I had to reflash it. Is there something I can do to prevent this from happening ?
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Topic summary

The discussion centers on the teardown, firmware modification, and protocol analysis of the TH08 LCD calendar/clock/temperature/humidity sensor powered by 3xAAA batteries with backlight, based on the BK7231N chip. The device is identified as a newer version of the TH06 model, featuring a TuyaMCU module communicating via a low-power Tuya serial protocol (version 00). Users successfully flashed OpenBK firmware without desoldering, enabling temperature, humidity, and battery monitoring with MQTT integration and NTP time synchronization. Key challenges included understanding the MCU-module communication, especially time synchronization commands and power management to optimize battery life. The MCU sends commands such as ObtainDPCache and ObtainLocalTime, with the WiFi module responding accordingly. Firmware updates improved battery consumption by ensuring the WiFi module powers down promptly after data transmission. The device’s RTC (U8) communicates with the MCU (U3) over a serial or I2C-like interface, with ongoing efforts to decode this traffic. Users experimented with modifying battery power sources, including LiPo and USB power mods with step-down regulators, confirming device operation at voltages between 3.3V and 4.5V. The Tuya app lacks options to adjust sensor reporting intervals, and attempts to change polling times via Tuya protocol commands were unsuccessful, likely due to firmware limitations. Serial sniffing and analysis tools like TuyaMCU Analyzer and SniffUART were used to decode dpIDs, confirming dpID 1 as temperature, dpID 2 as humidity, dpID 3 as battery state, and dpID 9 as Celsius/Fahrenheit setting. Firmware versions and MCU versions were compared, revealing some early versions had display update issues. The community contributed to improving OpenBK firmware to handle specific Tuya commands, including proper responses to WiFi signal strength queries, enhancing power management. MQTT integration with Home Assistant was refined, including battery level display improvements using LowMidHigh channel types. OTA updates and configuration changes require keeping the WiFi module powered, achievable via long button presses or hardware modifications. Attempts to use Tuya-cloudcutter for remote flashing were unsuccessful due to lack of matching profiles. Some users reported issues with sensor readings showing zero after flashing, possibly due to hardware revisions or firmware mismatches. Overall, the device is well-supported by OpenBK firmware with active community development focusing on power optimization, protocol decoding, and integration with home automation platforms.
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FAQ

TL;DR: “Flashing succeeds 100 % when CEN, RX and TX are isolated” and the Wi-Fi module stays powered just 18 s per cycle [Elektroda, spin55, post #20804765] Unit switch is dpID 9; send 55AA001000070101090400010026 to force °C [Elektroda, smoeller95s, post #21550660] Battery life rises from 3 days to 6 weeks after v1.17.302 fix [Elektroda, morgan_flint, post #20796796]

Why it matters: correct pinout, dpIDs and flags avoid soft-brick loops and halve power drain.

Quick Facts

• MCU board rev V3.7 (2023-11-06) uses step-down RT8008-like regulator, 2.3–3.6 V out [Elektroda, bogovik, post #21007162]
• Default Tuya baud: 9 600 bps; do **not** force 115 200 on battery models [Elektroda, bogovik, post #21007162]
• Wi-Fi on-time: 10–18 s (after dpCache fix) [Elektroda, p.kaczmarek2, post #20796796]
• Battery thresholds: High ≥ 4 V, Medium 4–3.1 V, Low < 3.1 V [Elektroda, morgan_flint, post #20804228]
• dpIDs: 1 Temp, 2 RH, 3 Batt-state, 4 Batt-%, 9 Unit, 10–13 limits, 14–15 alarms, 17–20 report/sensitivity [Elektroda, divadiow, post #21357234]

Which pads are Vcc, GND, TX, RX and CEN on TH08/TH08-B?

On CBx/CBU/CB3S modules the corner row is 1 GND, 2 3.3 V, 3 RX2, 4 TX2, 5 CEN (EN). Test pads marked RX1/TX1 belong to the Tuya-MCU and must be cut or unsoldered before flashing [Elektroda, morgan_flint, post #20929625]

How do I flash OpenBeken without desoldering?

Lift (or cut) MCU pins 8 (CEN) and 9/10 (RX/TX) or sever their traces. 2. Power the CBU with 3.3 V (battery V+ bypasses the regulator). 3. Run BK7231Flasher, back up, then write the QIO image at 921 600 bps. 4. Re-join the cuts with thin wire [Elektroda, spin55, post #21003945]

Device reboots endlessly after battery is flat – fix?

Safe-mode reset: toggle power 5 × within 5 s, connect to the OBK-AP, press “Exit safe-mode”, then set a working NTP server and MQTT host [Elektroda, morgan_flint, post #20919613]

Why does NTP show 1970 or 2070 date?

The LAN NTP IP must respond within the 18 s Wi-Fi window. Use e.g. ntp_setServer 217.147.223.78 and keep ntp_timeZoneOfs correct. Each failed packet logs NTP_SendRequest: Unable to send message [Elektroda, spin55, post #21074156]

How to switch the LCD from °F to °C?

Send the unit-convert dpID 9 packet once after boot:
delay_s 2
uartSendHex 55AA001000070101090400010026
Value 00 gives °C; 01 gives °F [Elektroda, smoeller95s, post #21550660]

MQTT values are 10× smaller – why?

Disable flag 33 (apply multiplier before publish). Otherwise temperature_div10 splits the MCU value and HA divides it again, giving 2.2 °C instead of 22 °C [Elektroda, p.kaczmarek2, post #21377733]

Can I map battery percentage to Home Assistant?

Yes.
setChannelType 4 BatteryLevelPercent
linkTuyaMCUOutputToChannel 4 val 4
After OBK 1.17.780 the HA discovery JSON includes this sensor automatically [Elektroda, p.kaczmarek2, post #21378297]

How to keep Wi-Fi on for configuration?

Hold the top button ≥ 3 s; Tuya-MCU holds CBU power high for ~90 s, enough for OTA or web-config [Elektroda, spin55, post #20804765]

What is dpCache and why use it?

Battery devices resend saved limits after every reboot. Mark a channel persistent with SetStartValue <ch> -1 and add 1 at the end of linkTuyaMCUOutputToChannel … to include it in the dpCache reply packet 0x10 [Elektroda, p.kaczmarek2, post #21385904]

Edge case – flashing stops at 70 % every time.

UM8005/UM805 (Tuya-MCU) toggles CEN mid-flash. Isolate CEN first or power the module through 3.3 V and ground while MCU ground is disconnected [Elektroda, spin55, post #21003945]