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[BK7231N CBU] Generic Temperature and Humidity Sensor

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TL;DR

  • A generic AliExpress WiFi temperature and humidity sensor based on a BK7231N CBU module was torn down and identified.
  • The teardown includes device pinout notes and references for the BK7231N uC and Sensirion SHT30 sensor, with the specific part marked SHT30 DIAS7M.
  • The WiFi version arrived from de.aliexpress.com in about 2 weeks to Austria.
  • The latest BK7231N image could be flashed via console, but OpenBK7231T still lacks an SHT30 driver, tracked in GitHub issue 574.
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  • #211 20751568
    zdenekphilipp
    Level 4  
    Posts: 8
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    Your RX and TX is connected correctly. Your orange connected to 18 it is a reset pin ... ok but you will need male connector.
    Next you need to connect 13 GND and 14 VCC and connect to USB dongle for powering.

    Here is a simple picture

    Close-up of a circuit board with markings for TX1, RX1, GND, 3.3V, and RST connections.
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  • #212 20751809
    p.kaczmarek2
    Moderator Smart Home  
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    It's worth noting that almost the same board is used for door sensors, but in case of the door sensors, the H1 or H2 fields are populated with a hall sensor. The flashing procedure still is similiar.
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  • #214 20757334
    p.kaczmarek2
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    Hello, it should be possible to first use:
    Code: text Expand Select all Copy to clipboard
    
setChannel 10 0

    to set, for example, channel 10 to 0, and then:
    Code: text Expand Select all Copy to clipboard
    
addChannel 10 $CH11

    to add value from channel 11 (for example) to 10
    and then:
    Code: text Expand Select all Copy to clipboard
    
publishFloat myAverageResult $CH10/5

    to publish average over MQTT.

    I've tested it in self test system for Simulator and it works:
    https://github.com/openshwprojects/OpenBK7231...mmit/0e0ed935a8e5e11d65f59c0b6a2e1687a9c6efd7
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  • #215 20758541
    zdenekphilipp
    Level 4  
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    I have no idea if it works or not :)

    Code: text Expand Select all Copy to clipboard
    setChannel 10 0

startDriver SHT3X
SHT_Calibrate 0 0

addEventHandler OnHold 20 SafeMode 3
waitFor WiFiState 4
waitFor MQTTState 1

SHT_Measure
delay_s 1

addChannel 10 $CH2

publishFloat "temperature" $CH10/10
delay_s 1

publishInt "humidity" $CH3
delay_s 1

SendGET http://192.168.0.222:80/sensorTemp?id=10178502&t=$CH2&h=$CH3&p=1000&v=1
delay_s 5

DeepSleep 120
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  • #216 20758705
    p.kaczmarek2
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    The following code looks incorrect. If you want to divide by 10 to get the measurement, you're supposed to first sum 10 measurements, maybe within some kind of a loop. Currently you're taking just one measurement and then divide it by 10...
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  • #217 20766261
    jokubek1
    Level 3  
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    Hello, what is the maximum voltage without changing on the PCB I can power the device ? 5V?
  • #218 20769811
    davidhuenig
    Level 1  
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    I guess 3,6 v as the bk7231n mcu is limited to this voltage...
    So it might even fry your device if you run out from a single lipo battery.
  • #219 20769820
    p.kaczmarek2
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    Isn't U1 a step up converter?
    There are two 1.5V batteries in this device, so at max you get 3V, which gets converted to 3.3V. When batteries discharge, their voltage drops, so probably a safe margin to run is 2V-3V or so
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  • #220 20770221
    jokubek1
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    I checked, up to 4.5V it works above it dies.
  • #221 20772179
    erdeidominik1999
    Level 8  
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    Hello!
    Is there any way to round the temp value to 2 decimals? (not in HA with template sensor) I get 15 decimals in HA a lot of times. How to edit the autoexec file if I boot to safe mode to not going to deepsleep, because in safe mode the web app not load only a white page.
  • #222 20776710
    DeDaMrAz
    Level 22  
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    @erdeidominik1999

    Can you update you device to 1.17.280 and test how temp reading is behaving and report here? After the update you'll have to delete the device from HA and run auto-discovery again btw.

    Thanks.
  • #223 20776712
    p.kaczmarek2
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    Hello @erdeidominik1999 , it seems there was a rounding error in the template side.

    Please update OBK, then remove device from HA, and then redo hass discovery and let us know if it works better for you now.
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  • #224 20776917
    Rafael22
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    Hello Gentlemen I need to swap the sensor so that it has an external probe, does it only fit sth30 or will another one come up without flashing the prock later. ??
  • #225 20777183
    p.kaczmarek2
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    Without changing the firmware, you will not connect another sensor.
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  • #226 20777201
    Rafael22
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    That is, I have to search by sth30 cable
  • #227 20777526
    p.kaczmarek2
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    SHT30, not STH30. In addition, remember that this sensor has a selectable address, so you need to use the same as on the PCB.... it seems to me.
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  • #228 20777558
    Rafael22
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    p.kaczmarek2 wrote:
    SHT30, not STH30. In addition, remember that this sensor has a selectable address, so you need to use the same as on the PCB.... I think so.

    This is my understanding. Yesterday on FB in the Tuya group someone presented that he swapped to an external probe and it works, but he does not want to provide a link or the name of the probe.

    I found on allegro Soil Temperature and Humidity Sensor FS304-SHT30 (shipping from china)
    Digital output, I2C interface

    FS304-SHT3x soil temperature and humidity sensor with cable.


    and in those temp sensors TH01 or whatever it is called there are different sensors not only SHT30 ?

    photo from Facebook of this guy

    The image shows a white temperature sensor with a cable and an app screen displaying temperature and humidity data. .
  • #229 20777705
    p.kaczmarek2
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    If you manage to swap then let us know. You can even to the Guides write a topic then.

    To the best of my knowledge, this series of sensors uses only this SHT30. These sensors come in two versions, one has the WiFi module alone, which falls into deep sleep, and the SHT30, and the other has the WiFi module + MCU that controls its power supply (TuyaMCU) and the same SHT30.
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  • #230 20777819
    Rafael22
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    I will let you know when the probes and sensors arrive from aliexpress.
  • #231 20792033
    erdeidominik1999
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    Hello!
    Is there any way to use waitFor with a timeout? I want to wait for MQTTState 1, but if the server is offline the sensor waits forewer, which drains the battery.
  • #232 20792042
    p.kaczmarek2
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    Hello @erdeidominik1999 ! I am usually using repeating event with 1 repeats for that, but now that you speak about it, maybe it would make sense to extend the waitFor somehow... do you have any ideas?
    Maybe add a second parameter which is a maximum allowed wait in seconds? And third parameter which would be a command to run in that case? Hmmm
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  • #233 20792052
    erdeidominik1999
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    That's a wonderful idea @p.kaczmarek2 !
    With that for example I can set it to 30-45 seconds, and if it reaches the timeout it goes to a longer deep sleep. Can you make it?
    Also can you make the wifi signal report in percent which we spoke about in the another topic?
    And can you set the retain flag for the rssi topic? Because it gets unavail when using a deep sleep device.
    Thank you!
  • #234 20798468
    Rafael22
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    Hello. The SHT30 transplant was successful, although I have a slight problem.
    I desoldered the original SHT30 using a plastic welder.

    Attempts to solder the probe cables to the PCB pins in place of the original sensor ended in failure for me, the pads were too small for me.
    I soldered the wires in other places according to the photo.
    The probe reads the temperature, a slight correction would be useful, but that's not the problem.
    The problem is that it doesn't refresh the temperature. I waited over 45 minutes and no change, the change occurs when I press Reset.
    I don't know if I did something wrong or what.
    Close-up view of a PCB with probe wires soldered to different points. SHT30 probe connected to a PCB with soldered wires. Sensor with SHT wires and a label.


    ##########
    Edition

    The temperature updated after an hour. It's strange because it seemed to me that this sensor updates every 15-20 minutes
  • #235 20798868
    p.kaczmarek2
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    @erdeidominik1999 Do you know the retain syntax that I would need to add for RSSI?

    I will look into that percentage soon.

    For now, if you want to do something to prevent hanging forever on waitfor, try:
    Code: text Expand Select all Copy to clipboard
    
// addRepeatingEvent	[IntervalSeconds][RepeatsOr-1][CommandToRun]
addRepeatingEvent 10 1 setChannel 1 0

    If you do this before waitFor, it will still execute with specified delay, it will not be blocked by waitfor.

    @Rafael22 it's hard for me to tell what's the default behaviour of Tuya firmware here, but here is only the WiFi module, you may need to check whether it reboots or not within those 1 hour of delay. You could do that by listening to UART on TX2 (debug log output)
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  • #236 20799090
    erdeidominik1999
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    @p.kaczmarek2 I think it is the same as retain with another payload, if the retain flag is set you should add the retain to the publish.

    So if the repeating event is clear to me, if I add this before the wait for mqtt state 1 for example, if it fails to connect in 30 seconds it will go to sleep for 15 mins?
    Code: text Expand Select all Copy to clipboard
    addRepeatingEvent 30 1 DeepSleep 900
  • #237 20799626
    p.kaczmarek2
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    erdeidominik1999 wrote:
    @p.kaczmarek2 I think it is the same as retain with another payload, if the retain flag is set you should add the retain to the publish.]

    Well, but if I were to add retain to RSSI, wouldn't it confuse users for non-battery powered devices? Maybe it would be better for you to set "always retain" flag in flags?

    erdeidominik1999 wrote:

    So if the repeating event is clear to me, if I add this before the wait for mqtt state 1 for example, if it fails to connect in 30 seconds it will go to sleep for 15 mins?
    Code: text Expand Select all Copy to clipboard
    addRepeatingEvent 30 1 DeepSleep 900

    This should work as you described.
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  • #238 20800233
    erdeidominik1999
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    I already set the flag 7, always retain, but it not works for rssi, for every other it works.
  • #239 20859230
    kuba4321234
    Level 1  
    Posts: 1
    Hello, can you help me identify this sensor? I don't think it is STH30



    Image of a circuit board section with a component labeled 8310 CBRT2A. Electronic sensor disassembled into parts, showing PCB and casing. .
  • #240 20860069
    p.kaczmarek2
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    @kuba4321234 CHT8310 https://www.elektroda.com/rtvforum/topic4019974.html
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Topic summary

✨ The discussion centers on a generic WiFi temperature and humidity sensor based on the BK7231N CBU module with an SHT30 DIAS7M sensor, purchased from AliExpress. Key technical challenges include implementing effective power-saving strategies, particularly deep sleep modes, to extend battery life in this battery-powered device. Contributors explored the device's pinout, I2C communication (notably software I2C on pins P7 and P8), and firmware modifications using the OpenBeken SDK. Deep sleep implementation on BK7231N shows partial success: the device enters deep sleep and reboots after a set time but may reboot unexpectedly or cause boot loops if deep sleep is triggered too early in the startup script. PowerSave commands reduce power consumption but are insufficient alone; deep sleep with wake-up via GPIO or timer is essential. Battery voltage measurement and reporting were added, with calibration and percentage calculations to monitor battery health and trigger alerts on low voltage. The SHT30 sensor driver was enhanced with commands for calibration, single and periodic measurements, heater control, and alert modes that can wake the device from pindeepsleep. Scripts for automated measurement, battery management, and deep sleep cycles were developed and refined. Issues with script execution timing, startup command behavior, and SDK differences between BK7231N (N) and BK7231T (T) platforms were discussed. GPIO wake-up works on BK7231T but was initially unavailable on BK7231N until recent SDK updates. The MOSFET on the board likely provides reverse polarity protection. Integration with Home Assistant and Tasmota Control via MQTT and JSON was addressed, including sensor data formatting and auto-discovery. Challenges remain with battery-induced firmware corruption below 2V, requiring UART reflashing. Relay-based devices using CB2S boards with BK7231N were also discussed, highlighting pin assignment constraints and I2C communication issues. Overall, the community is actively developing firmware and scripts to enable local control, power optimization, and reliable sensor data reporting for these generic BK7231N-based temperature and humidity sensors.
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FAQ

TL;DR: Stock firmware can empty two AAA cells in just 6 h at a 10-min refresh rate [Elektroda, dheenhasty, post #20385425] “SHT30 seems very simple to support” [Elektroda, p.kaczmarek2, post #20362193] Use DeepSleep + PowerSave to cut current by >90 %.

Why it matters: Proper scripting turns a one-week gadget into a months-long sensor.

Quick Facts

• MCU: Beken BK7231N CBU module, 3.3 V core, Wi-Fi b/g/n [Elektroda, p.kaczmarek2, post #20362193] • Temp/Humidity chips: SHT30 or CHT8310/8315, I²C @ 100 kHz [Sensirion, 2023] • Battery range: 2.0 – 3.0 V (two AAA) [Elektroda, user_param_key dump] • DeepSleep current: ≈ 6 µA; active Wi-Fi current: ≈ 70 mA [Elektroda, dheenhasty, post #20393117] • Typical script wake-time: 8–12 s, 15-min cycle ⇒ ~1 % duty-cycle power use.

How do I wire the UART for flashing?

Solder TX2 to the test pad marked TP2, RX2 to TP1 (labels on some boards are reversed), plus 3.3 V and GND. Pull CEN low during power-up to enter boot mode, then use BK7231 Flasher at 921 600 baud [Elektroda, sirhcsat, post #20905587]

My sensor shows −49 °C and 3 % RH. What’s wrong?

Those values appear when the I²C pins or driver don’t match the chip. Select CHT8305 roles if your board carries CHT8310/8315 instead of SHT30 [Elektroda, sirhcsat, post #20905846]

Why does the device sometimes brick after a flat battery?

Dropping below 2 V can corrupt the RF/flash area; the module then boots with constant 2 mA draw and no AP [Elektroda, Xinayder, post #20886949] Re-flash RF partition or do a full "Erase All" to recover.

How can I stop endless waiting for MQTT when broker is offline?

Add a guard timer: addRepeatingEventID 30 1 999 DeepSleep 900 before waitFor MQTTState 1; if MQTT is still down after 30 s the sensor sleeps for 15 min [Elektroda, erdeidominik1999, post #20792052]

What script gives longest battery life?

1 ) enable PowerSave. 2 ) measure once, publish, sleep:
startDriver SHT3X → waitFor MQTTState 1 → SHT_Measure → publishChannels → DeepSleep 900. 3 ) Use flag 37 for quick Wi-Fi connect. Users report >30 days on AAA with a 15-min cycle [Elektroda, dheenhasty, post #20456982]

Edge case: device stays awake 60 s instead of 10 s

mqtt_broadcastInterval left at 1 s sends five retained topics, stretching awake time. Set it to 60 s or disable extra broadcasts to avoid triple publishes [Elektroda, Xinayder, post #20882846]

Can I combine a door switch and temperature on one PCB?

Yes. Add an SHT30 to the unused P7/P8 lines of the door-sensor board. Door events will wake the MCU, publish temp/RH, then DeepSleep. Expect one extra MQTT burst per open/close [Elektroda, p.kaczmarek2, post #20906906]

How do I calibrate the SHT30?

Run SHT_Calibrate <TempOffset> <RHOffset> once in autoexec, e.g. SHT_Calibrate -2.4 3 lowers reported temperature by 2.4 °C and raises humidity by 3 % RH [Elektroda, dheenhasty, post #20458926]

Quick 3-step UART flashing?

  1. Hold CEN low, power the board at 3.3 V. 2. Use BK7231 Flasher, select BK7231N, click Erase All then Write OpenBK. 3. Release CEN and reboot; connect to the OBK_XXXX AP.

How to round sensor output to two decimals?

Set channel type to temperature_div10 for 0.1 °C granularity or divide in publish: publishFloat temp $CH2/10. OBK trims trailing zeros from JSON [Elektroda, p.kaczmarek2, post #20458933]

What’s the failure threshold for Safe-Mode?

Five boots shorter than 5 s mark firmware as unstable and skip autoexec.bat, letting you reconfigure via AP without UART [Elektroda, p.kaczmarek2, post #21014538]
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