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

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):


Anyway, that's a good mod, and if you need any help with extending it, let me know.

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=?????".

I think our OBK channels command should work:

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

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.

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.

I'm eager to hear some feedback! Please try and let know.

PS: Don't use PowerSave 1 with it.

@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

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.

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?

I've always done it like this:



seen in my pic here
https://www.elektroda.com/rtvforum/topic4062365.html#21158431

>>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.

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?

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?

I thought powersave 1 was OK now with DS1820? https://www.elektroda.com/rtvforum/topic4056286-30.html#21190145

@max4elektroda

>>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?

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:

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.

>>21238199

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

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.

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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?
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B.T.W: How can temperature value be read as a HTTP request?

What's this in log:

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

it keeps repeting about once every second.