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Adding a DHT22 Temperature Sensor to T34/BK7231N for Room Heating Control

Tilator 3066 19

TL;DR

  • Modified a T34/BK7231N heater controller by adding a DHT22 temperature sensor for room-temperature sensing and relay-based heating on/off control.
  • Wired the sensor to the S1/S2 external switch connector: S1 to ground, S2 to GPIO P14/pin 11, removed the sensor’s NC pin, and used jumper power for VCC.
  • Removed the pullup resistor and capacitor on P14 near the relay under marking BC8, and flashed without desoldering the CPU by soldering UART to BR4.
  • The DHT22 reported correct values immediately; a DHT11 also worked only with divider adjustments.
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  • Modified Tuya relay controller with attached DHT22 sensor.
    Hello,

    There seems to be multiple different layouts available of this device.

    My need was to add a temperature sensor in it to make possible to measure room temperature and use the relay to connect heating on and off.

    Smart switch Tuya with DIY modification, label view.

    There is S1 and S2 connectors for external switch. I used those to connect DHT22 sensor. S1 is ground and S2 ic connected to GPIO P14, which is pin11 on the CPU. I just took the NC pin off the sensor. All three other pins are at suitable distance from each other to fit the connector.

    There is a pullup resistor and capacitor between this P14 and VCC. I took them both off. They are located near the relay under marking BC8.

    Modified Tuya relay controller with attached DHT22 sensor.

    Only VCC to the sensor needs to be addeb by jumper.

    I did not desolder the CPU to flash it. One UART wire can be soldered to the BR4 resistor at the end near number 4. For the second one I used a big and sharp normal knitting needle from my wifes reserves. I holded it at the plase simply by hand. It's easier to keep it on the right spot if it is sharp enoug.

    DHT22 sensor gives right values right away. I did try a DHT11 too and it seems to need some dividers to give correct value.

    Here is what it looks like:

    Web interface of the BK7231 controller with DHT22 sensor information

    Here is configuration:

    Screenshot of pin configuration settings for BK7231N/BK7231T controller.

    DHT22 is where originally should be BTN_TGL_ALL to act as external on/off switch.

    Related T34 topic (flashing method): https://www.elektroda.com/rtvforum/topic4036975.html
    For more info, see: https://www.elektroda.com/rtvforum/find.php?q=T34

    Cool? Ranking DIY
    About Author
    Tilator
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    Tilator wrote 130 posts with rating 13, helped 2 times. Been with us since 2023 year.
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  • #2 21095677
    p.kaczmarek2
    Moderator Smart Home  
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    Yes, this is a good idea. With OBK, such modifications are very easy. We've did similiar thing with DHT11 on our YT channel:
    https://www.youtube.com/watch?v=KEjOPuYd3CE
    The second modification that is worth considering is adding a IR receiver, one could be taken from any scrap board from devices like a sat tuner, etc:



    However, when it comes to IR receivers, I would first check what kind of device we're extending. That's because IR code may not work well with PowerSave, while on the other hand, some devices may straight up require PowerSave because of their low quality power supplies. That's why IR mod may be a little bit more problematic.

    By the way, now you have a temperature values read. This means you could now write some kind of simple script in autoexec.bat to control relay depending on the temperature. For example, turn on heating when it's too cold...
    https://github.com/openshwprojects/OpenBK7231T_App/blob/main/docs/autoexecExamples.md

    There is, however, one more important thing that needs to be mentioned. This particular device you have does not provide isolation from the mains, and it means that you can get live mains on like DHT11 ground pin. This means you must exercise EXTREME CAUTION while doing and using such mods. So, of course, modify only devices disconnected from mains and futhermore make sure that your DHT (or any attached sensor) is well secured and won't make contact with user... or anything else. In your case this part needs to be isolated/secured (if that's a final connection):
    Close-up of an electrical circuit with a DHT11 sensor.

    Anyway, that's a good mod, and if you need any help with extending it, let me know.
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  • #3 21095702
    Tilator
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    p.kaczmarek2 wrote:
    There is, however, one more important thing that needs to be mentioned. This particular device you have does not provide isolation from the mains, and it means that you can get live mains on like DHT11 ground pin. This means you must exercise EXTREME CAUTION while doing and using such mods. So, of course, modify only devices disconnected from mains and futhermore make sure that your DHT (or any attached sensor) is well secured and won't make contact with user... or anything else. In your case this part needs to be isolated/secured (if that's a final connection)


    You are right and I'm aware of it. The cap you can see is only there to demonstrate the connection. Final installation needs some glue between the parts.

    Can you tell me is it possible to read the temperature value by some http command like "http://My_Device/cm?cmnd=?????".
  • #4 21095708
    p.kaczmarek2
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    I think our OBK channels command should work:
    Code: text Expand Select all Copy to clipboard
    
http://192.168.0.163/cm?cmnd=channels

    Please try it out and let me know if it works for you.
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  • #5 21095714
    Tilator
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    p.kaczmarek2 wrote:
    I think our OBK channels command should work:
    Code: text Expand Select all Copy to clipboard
    
http://192.168.0.163/cm?cmnd=channels

    Please try it out and let me know if it works for you.


    Thanks.
  • #6 21179203
    Tilator
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    Hello again,

    There seems to be DS18B20/DS1820 support available now.

    Thank you again. This was good add on it.

    I have not tested it yet, but will do it as soon as I have a bit spare time.
  • #7 21180233
    p.kaczmarek2
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    I'm eager to hear some feedback! Please try and let know.

    PS: Don't use PowerSave 1 with it.
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  • #8 21223436
    divadiow
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    @Tilator does your DHT22 give readings still with the latest builds? I don't suppose you ever took a pic of the PCB inside the casing? I'm just curious about my one which doesn't seem to work with OBK but does with Tasmota. Maybe mine is fake and the Tasmota driver has different tolerances or something

    Close-up of a PCB with visible electronic components.
  • #9 21223462
    Tilator
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    divadiow wrote:
    @Tilator does your DHT22 give readings still with the latest builds? I don't suppose you ever took a pic of the PCB inside the casing? I'm just curious about my one which doesn't seem to work with OBK but does with Tasmota. Maybe mine is fake and the Tasmota driver has different tolerances or something


    At least version version 1.17.661 works fine.

    Pictures are available if they anyhow help you.
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  • #10 21237109
    Tilator
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    p.kaczmarek2 wrote:
    I'm eager to hear some feedback! Please try and let know.


    Now I had time to try it, but DS18B20 sensor does not come available.

    There are at least two different physical configurations to install this sensor. Which one should I use?

    I installed it by connecting GND + VDD to ground and mid pin to GPIO. Does it need to have power from VDD pin or should GPIO power it as it's supposed to do in this "two wire" connection?
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  • #12 21237369
    Tilator
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    >>21237328

    I did try that too without good outcome.

    I have this T34 SOC and I try to use GPIO 11 which is UART TX. Might there be some setting wrong related to that?

    Added after 5 [hours] 11 [minutes]:

    Seems I can't get it working. I did try a couple different pull up resistors and I also tried two different GPIOs. DHT22 sensor works fine connected to both of them, but DS18B20 does not connected to either.
  • #13 21237883
    p.kaczmarek2
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    So, to sum up, you are using GPIO 11 which is UART TX and:
    - DHT22 works there
    - LED (to blink it, as Rel role or LED role) works as well
    - but DS18B20 doesn't work?

    Added after 34 [seconds]:

    Maybe you have PowerSave on and need to try turning it off?
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  • #14 21237985
    Tilator
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    p.kaczmarek2 wrote:
    So, to sum up, you are using GPIO 11 which is UART TX and:
    - DHT22 works there
    - LED (to blink it, as Rel role or LED role) works as well
    - but DS18B20 doesn't work?


    Yes, and on top of thet GPIO 9 works with DHT22 too but not with DS18B20.

    p.kaczmarek2 wrote:

    Maybe you have PowerSave on and need to try turning it off?


    How can I find out if it's on?
  • #16 21238199
    Tilator
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    >>21238012

    Can you tell does the driver give sensor enough power by pulling GPIO line up or does it still need other external power and pull up resistor?
  • #17 21238801
    Tilator
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    I took one of those mini relays having BK7231N and connected DS18B20 to it using GBIO 9. Still no temperature reading.

    If I add sensor usin WEB UI there happens nothing. No loaded driver listed on front page. If I put a startup command "startdriver DS1820 9" and reboot it does load driver but temperature reading is always same -1,26 C or something like that.

    I did try one wire connection having only ground and data connected and VDD connected to ground. Then I did try "two wire" connection having power connected to VDD with or without pull up resistor.

    Always same result. T34 device has a power metering component, but this latter device doesn't even have it.

    B.T.W: I made a little modification to make it easier to try adding this sensor. Here are pictures about it in case someone is interested: Small, bent wire on a white surface next to a black handle tool. The image shows the back of a green circuit board with a soldered wire. Colorful circuit board with a thin leg soldered onto it.

    In the first picture there is a tiny "hook". It's originally a leg from one DHT22 sensor. It is narrow enough, soft to bend and easy material to solder.

    In second picture this hook has been soldered to pin 25 (GPIO 9) and third picture has a drop of super glue to attach it firmly.
  • #18 21238822
    divadiow
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    >>21238199

    still requires external power afaik
    so, 3.3v, gpio and ground. 4.7kohm between data and vcc.
  • #19 21238824
    Tilator
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    divadiow wrote:
    >>21238199

    still requires external power. 3.3v, gpio and ground. 4.7kohm between data and vcc.


    Thanks.

    A bit new info:

    I got some readings from BK7231N device and the tric was to give it a bit higher voltage. 4,75V. Even thogh the values it gove were a bit high somewhere above 33 C while actual temperature is about 10 degrees lower.

    Stll nothing from T34. Not even using higher voltage.

    The driver seems to act a bit different for different platforms. Is it sure, it recognizes T34 based platform right? Should it act as a BK7231N too?

    I made some more testing using both those devices and result is same for them: Giving the sensor 3,3V and nothing happens. Giving 4,75V and it comes up. 4,7k pull up resistor in all tests.

    ************************
    Still more testresults:

    It works with 3,3V too if it is set up in both the WEB UI and startup command. Start up command can even be set to a wrong GPIO.

    Does it sound like a timing problem?
    *************************

    B.T.W: How can temperature value be read as a HTTP request?
  • #20 21348605
    Tilator
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    What's this in log:

    Info:SENSOR:DHT start, pin is 6
    Info:SENSOR:DHT checksum failure!

    it keeps repeting about once every second.
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Topic summary

✨ The discussion focuses on integrating a DHT22 temperature sensor with T34/BK7231N-based devices for room heating control via relay switching. The user connected the DHT22 sensor to S1 (ground) and S2 (GPIO P14/pin 11 CPU) after removing a pull-up resistor and capacitor near the relay (marked BC8). The device firmware supports reading temperature values, enabling relay control through scripts (e.g., autoexec.bat). HTTP commands like "/cm?cmnd=channels" can retrieve sensor data. Later, DS18B20 sensor support was introduced, but users reported difficulties with DS18B20 on T34 devices, including no temperature readings despite correct wiring and driver loading. DS18B20 requires external 3.3V power, ground, data line with a 4.7kΩ pull-up resistor; some users found better results with slightly higher voltage (~4.75V). PowerSave mode may interfere with sensor operation, especially for IR receivers and DS18B20. DHT22 works reliably on GPIO pins including UART TX (GPIO 11) and GPIO 9, while DS18B20 does not. Firmware versions (e.g., 1.17.661) support DHT22 well. Troubleshooting includes checking power supply, pull-up resistor presence, GPIO configuration, and disabling PowerSave. Error logs show occasional DHT checksum failures. Modifications to the PCB and sensor connections were shared with photos for community reference.
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FAQ

TL;DR: With 3 wires and one jumper, you can add a DHT22 to a T34/BK7231N relay for room heating control; one expert warning is, "does not provide isolation from the mains." This FAQ helps OBK users wire the sensor, flash the board, read temperature over HTTP, and avoid DS18B20 troubleshooting traps such as PowerSave and fixed -1.26 C readings. [#21095677]

Why it matters: This mod turns a low-cost relay module into a room thermostat, but incorrect wiring or insulation can expose live mains on the sensor side.

Option Wiring result in thread Reported behavior Best use here
DHT22 S1 = GND, S2 = GPIO P14, add VCC jumper Worked immediately and gave correct values Easiest room-temperature control
DHT11 Similar class of sensor Needed dividers for correct values Less convenient
DS18B20 Needed 3.3V or even 4.75V in tests, plus pull-up Often failed or showed fixed values Harder to integrate

Key insight: DHT22 was the only sensor in the thread that worked reliably on both the T34 and BK7231N setups without extended debugging. DS18B20 support existed later, but setup consistency and power behavior were the main failure points.

Quick Facts

  • The successful DHT22 mod reused the S1/S2 external switch pads, with S1 as ground and S2 tied to GPIO P14, which is pin 11 on the CPU. [#21095664]
  • On the T34 board, the pull-up resistor and capacitor connected between P14 and VCC were removed; they sit near the relay under the BC8 marking. [#21095664]
  • A working DS18B20 setup reported in the thread used 3.3V + GPIO + GND and a 4.7 kOhm pull-up between data and VCC. [#21238822]
  • One tester reported DS18B20 stayed dead at 3.3V but started responding around 4.75V, although the reported temperature was about 10 C too high at first. [#21238824]

How do I wire a DHT22 to a T34 or BK7231N board using the S1 and S2 external switch pads for room temperature control?

Wire the DHT22 to the external switch pads by using S1 as GND and S2 as GPIO P14. Remove the sensor’s NC pin, then connect the other three pins so they fit the connector spacing. Add only a VCC jumper for power. This setup let the relay board measure room temperature and switch heating on and off in OBK. [#21095664]

Which pull-up resistor and capacitor need to be removed on the T34 board when connecting a DHT22 to GPIO P14?

Remove the pull-up resistor and capacitor that sit between GPIO P14 and VCC. In the thread, they are described as the two parts near the relay under the BC8 marking. After removing them, the DHT22 on P14 gave correct readings right away. [#21095664]

What is OpenBK7231T_App (OBK), and how does it help with adding sensors like DHT22 or DS18B20 to BK7231N devices?

OBK is the firmware used in the thread to assign GPIO roles, load sensor drivers, and automate relay logic from temperature input. "OpenBK7231T_App (OBK) is firmware that runs on BK7231-based smart devices, exposes GPIO configuration and drivers, and lets users add functions like DHT22, DS18B20, relays, and HTTP control without redesigning hardware." The thread states such modifications are very easy with OBK. [#21095677]

What is PowerSave 1 in OBK, and why can it affect IR receivers or DS18B20 temperature sensor operation?

PowerSave 1 is an OBK power-saving mode that can break timing-sensitive peripherals. The thread warns that IR codes may not work well with PowerSave, and later adds a direct note: do not use PowerSave 1 with DS18B20. "PowerSave 1 is a low-power operating mode that reduces activity to save energy, but that timing change can disrupt peripherals that need stable sampling or pulse timing." [#21180233]

How can I flash a T34/BK7231N device without desoldering the CPU, and where are the UART points mentioned in the thread?

You can flash it without removing the CPU by soldering to exposed UART points. 1. Solder one UART wire to the BR4 resistor, at the end near number 4. 2. Touch the second UART point manually; the thread used a sharp knitting needle. 3. Hold contact in place while flashing. This method was reported to work on the T34 board. [#21095664]

Why does a DHT22 work on GPIO 9 or GPIO 11 in OBK while a DS18B20 on the same pins gives no reading?

Because the thread shows the GPIOs themselves were not the problem. The same user confirmed DHT22 worked on GPIO 11 and GPIO 9, while DS18B20 failed on both. That points to DS18B20-specific issues such as driver startup, PowerSave, wiring mode, or power level rather than a dead pin. [#21237985]

What is the correct DS18B20 wiring on a BK7231N or T34 device: normal 3-wire mode or parasite-powered 2-wire mode?

Use normal 3-wire mode for this thread’s hardware. The practical recommendation was 3.3V, GPIO, and GND, plus a 4.7 kOhm resistor between data and VCC. The user tested parasite-style wiring and separate VDD wiring, but stable advice in the thread favored external power, not GPIO-powered operation. [#21238822]

How do I check whether PowerSave is enabled in OBK when troubleshooting a DS18B20 sensor that is not detected?

The thread does not give a menu path or HTTP command to check that state. It only suggests PowerSave as a likely cause and asks whether it should be turned off when DS18B20 works nowhere but DHT22 works on the same GPIOs. In this thread, PowerSave is a troubleshooting clue, not a documented diagnostic procedure. [#21237883]

What HTTP command in OBK returns the current temperature reading from a DHT22 or DS18B20 sensor?

The only HTTP command proposed in the thread is the OBK channels query: http://192.168.0.163/cm?cmnd=channels. That command was suggested specifically when the user asked how to read temperature by HTTP. The thread does not show a later confirmation or an example response payload. [#21095708]

Why does the DS18B20 driver in OBK show a fixed reading like -1.26 C, and what does that indicate?

A fixed reading like -1.26 C indicates the driver loaded but did not get a valid sensor reading. The user reported that startdriver DS1820 9 made the driver appear after reboot, yet the temperature stayed fixed at about -1.26 C. In this thread, that behavior matched a detection, timing, or power problem rather than a working sensor. [#21238801]

DHT22 vs DS18B20 for room heating control on a T34 relay board: which sensor is more reliable and easier to integrate?

DHT22 was more reliable and easier to integrate in this thread. It worked immediately on the T34 mod, returned correct values, and also worked on GPIO 9 and GPIO 11 in later tests. DS18B20 support appeared later, but multiple tests still produced no reading, a fixed -1.26 C, or unstable behavior. [#21238801]

Why might a DS18B20 start working only at about 4.75V but fail at 3.3V on some BK7231N-based devices?

The thread points to a power or timing sensitivity in the actual setup. One user reported no DS18B20 response at 3.3V, then partial operation at about 4.75V, with a reading roughly 10 C too high. The same post notes it later worked at 3.3V when configured in both the Web UI and the startup command, which strongly suggests a startup timing issue. [#21238824]

How should exposed DHT22 or DS18B20 wiring be insulated on a non-isolated mains-powered T34 module to make the mod safer?

Insulate and secure every exposed sensor connection so it cannot touch the user or nearby parts. The thread gives a blunt warning: the T34 board does not provide isolation from the mains, so live mains may appear on the sensor ground. One expert warning says, "does not provide isolation from the mains," so the final installation should be glued or otherwise fixed in place, not left exposed. [#21095677]

What could cause repeated OBK log messages like 'Info:SENSOR:DHT checksum failure!' every second on a DHT sensor setup?

That message means OBK is polling the DHT sensor, but the data frame fails checksum validation each cycle. In the thread, the log repeats about once every second, which matches continuous retry behavior. Common thread-level causes are incorrect wiring on the sensor pins, leftover passives on the GPIO path, or an unstable physical connection after the hardware mod. [#21348605]

How does OBK detect and handle the T34 platform compared with a standard BK7231N device when loading the DS1820 driver?

The thread does not show a confirmed platform-detection difference between T34 and standard BK7231N for DS1820 loading. The user explicitly asked whether T34 was recognized correctly and whether it should act as BK7231N too, but no final technical answer appears. What the thread does show is inconsistent DS1820 behavior on both board types, so no T34-specific handling was confirmed. [#21238824]
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