FAQ
TL;DR: 5 µA standby current, “WiFi module draws 6 µA in deep sleep” [Elektroda, p.kaczmarek2, post #20564338], lets the TH01/TH08 run over a year on two AAA cells. Use TuyaMCU IDs 1-3, 17-18, flash OpenBeken, map channels, then Home-Assistant auto-discovers it. Why it matters: you get cloud-free, battery-friendly sensing for <$10.
Quick Facts
• MCU module: Tuya CB3S (BK7231N, 2 MB flash) [Elektroda, p.kaczmarek2, post #20564338]
• Sensor IC: Sensirion SHT30, ±0.3 °C, ±2 % RH typical *“SHT3x-DATASHEET”*
• Sleep current: 5 µA (MCU only), 6 µA (Wi-Fi deep sleep) [Elektroda, p.kaczmarek2, post #20564338]
• Reporting interval: 1–120 min adjustable via dpIDs 17 & 18 [Elektroda, p.kaczmarek2, post #20564338]
• Flash time: ≈15 s at 1.5 Mbps using BK7231 GUI Flasher [Elektroda, xPawelski, post #21233509]
What dpIDs hold temperature, humidity and battery level?
dpID 1 carries temperature in °C×10, dpID 2 carries humidity in %, dpID 3 is battery state (0 = low, 1 = mid, 2 = high) [Elektroda, p.kaczmarek2, post #20564338]
Why do I get only zeros after flashing?
The UART between MCU and CB3S must be isolated during flashing; otherwise the MCU powers the Wi-Fi module parasitically and stops measurements. Unsolder or cut the RX/TX resistors, flash, then restore the link [Elektroda, woszu, post #20739869]
How do I store a channel value across reboots?
Issue SetStartValue -1. The “-1” flag forces OpenBeken to write the last value to flash and reload it next power-up [Elektroda, p.kaczmarek2, post #20973103]
Can I change the reporting frequency from Home Assistant?
Yes. Map dpID 17 (temperature period) and 18 (humidity period) as dpCache variables, then edit the corresponding text fields exposed via MQTT/HA; 60 means 60 minutes. The MCU requests the cached value on every wake-up [Elektroda, p.kaczmarek2, post #20564338]
What’s the quickest safe flashing method?
- Feed CB3S with 3.3 V directly, set BK7231 GUI Flasher to 1 500 000 baud. 2. Hold RESET every 2 s to keep the module awake. 3. Write the latest OpenBeken QIO binary (~15 s). This avoids cutting tracks and works on firmware 2.1.8 [Elektroda, xPawelski, post #21233509]
Edge case: sensor wakes but sends no TuyaMCU packets—what now?
Firmware 2.1.8 sometimes disables the MCU TX line; toggling Flag 26 (alternate UART) forces bootloader mode and restores communication [Elektroda, xPawelski, post #21233509]
How long does a pair of AAA batteries last?
At 5 µA standby and a 60 s Wi-Fi burst every 15 min (≈80 mA s), average current is ≈25 µA; 1000 mAh alkalines last ≈1600 h ≈ 2 months. Extending the interval to 60 min pushes life beyond one year [“Designing for Low Power”, 2023].
Is an external probe supported?
Not natively. The on-board SHT30 uses I²C at MCU level; CB3S sees only TuyaMCU data. Without hardware re-design you cannot swap in a DS18B20 or wired SHT probe [Elektroda, p.kaczmarek2, post #21333979]
Which pins are available on the CB3S for hacking?
UART1 TX/RX (pins 16/15), GPIO 6–14, 24, 26, ADC 3, VCC and GND are broken out; most are free because battery devices let the external MCU handle sensors [Elektroda, table, post #20564338]
What happens if dpCache is empty?
The Wi-Fi module replies with 0x10 command length-0, meaning “no cached settings”; the MCU then keeps its previous interval. This state is normal after factory reset [Elektroda, p.kaczmarek2, post #20584528]
How do I map the Tuya variables in OpenBeken?
Insert into autoexec.bat:
startDriver TuyaMCU
startDriver tmSensor
setChannelType 1 temperature_div10
linkTuyaMCUOutputToChannel 1 val 1
setChannelType 2 Humidity
linkTuyaMCUOutputToChannel 2 val 2
setChannelType 3 ReadOnlyLowMidHigh
linkTuyaMCUOutputToChannel 3 enum 3
Home Assistant will discover three entities automatically [Elektroda, p.kaczmarek2, post #20564338]
Can I flash through Cloudcutter instead?
Yes, but BK7231 battery devices often drop power mid-transfer, making success rates below 30 % per user test [Elektroda, xPawelski, post #21233509] USB-UART flashing with power held high is faster and safer.
Quote worthy advice before you start?
“Keep the MCU asleep while you flash; waking it at the wrong time feeds phantom volts and scrambles UART” [Elektroda, woszu, post #20739869]
