Additional info about the temperature sensor

[Mariuccio112]

Hi,
Would be possible for you to share additional information about the temperature sensor, like pinout?
Thanks

[rubenbe]

Hi,

Honestly, I've never looked into detail into that pinout.

Do you have a fan and/or sensor? Otherwise with an oscilloscope or logic analyzer it should fairly easy to find out.

I suspect, there is

• two i2c pins
• one or two pins to toggle the LED
• two pins for power/GND.

What is your goal? To make a cheaper version?

[Mariuccio112]

I have a fan Viessmann one, I want to try to replace the touch interface with your implementation. I just saw on your post about the sensor, and I check online and the price is incredible high for if is only an sht21. So yes my idea will be to do a cheaper version.The sensor normally has only 4 pins, of which 2 signal. I don’t have an oscilloscope to test the fan with.Regards Il giorno 14 giu 2025, alle ore 10:34, rubenbe ***@***.***> ha scritto:rubenbe left a comment (rubenbe/comfospottwin40#14) Hi, Honestly, I've never looked into detail into that pinout. Do you have a fan and/or sensor? Otherwise with an oscilloscope or logic analyzer it should fairly easy to find out. I suspect, there is two i2c pins one or two pins to toggle the LED two pins for power/GND. What is your goal? To make a cheaper version? —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[rubenbe]

Hmm, mine is currently installed, so I can't easily access it.

If you have a multimeter you should be able to find the GND and the voltage (3.3 / 5V)
If the voltage is very unstable it is probably the I2C (if it is very repetitive probably the LED)

When you have found the non-stable ones, you can use a LED and a resistor to find out more about the signal.

If you can wait a bit, I'll have a look at my setup in the coming weeks. (probably early July)

[Mariuccio112]

That will be great, in meantime I’ll try to get a logic analyzer to monitor the connectionIl giorno 14 giu 2025, alle ore 16:29, rubenbe ***@***.***> ha scritto:rubenbe left a comment (rubenbe/comfospottwin40#14) Hmm, mine is currently installed, so I can't easily access it. If you have a multimeter you should be able to find the GND and the voltage (3.3 / 5V) If the voltage is very unstable it is probably the I2C (if it is very repetitive probably the LED) If you can wait a bit, I'll have a look at my setup in the coming weeks. (probably early July) —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[rubenbe]

Good luck! Let me know the progress.

FYI: I used this to reverse engineer the protocol:
https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview

It is not too expensive (especially if you compare it to a stupid temperature sensor ;) )
And it combines analog and simple logic analyzer functionality.
I have no affiliation to the company.
Perfect for simple home usage.

[Mariuccio112]

Thanks for the info!Il giorno 14 giu 2025, alle ore 18:19, rubenbe ***@***.***> ha scritto:rubenbe left a comment (rubenbe/comfospottwin40#14) Good luck! Let me know the progress. FYI: I used this to reverse engineer the protocol: https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview It is not too expensive (especially if you compare it to a stupid temperature sensor ;) ) And it combines analog and simple logic analyzer functionality. I have no affiliation to the company. Perfect for simple home usage. —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[haraldfunk]

Hello, I just had the same idea a few days ago. I plan to install 6 fans in 3 zones in the next weeks and also found the simple sensor way too expensive to order 3 of them. I just ordered one which will arrive this week.
My plan is to reproduce it twice to have one for every zone.
Based on the pictures I found on the internet, the pcb should be fairly simple.
I would be very happy to share my pinout (and maybe some gerber files for the pcbs) in the next few weeks.

I read that others had issues bringing their setups to life with more than one sensor, but I will either way go with the standard controller first and try to replace it with this solution here later on when i have more free time.

[Mariuccio112]

Waiting for your feedbackIl giorno 15 giu 2025, alle ore 23:06, haraldfunk ***@***.***> ha scritto:haraldfunk left a comment (rubenbe/comfospottwin40#14) Hello, I just had the same idea a few days ago. I plan to install 6 fans in 3 zones in the next weeks and also found the simple sensor way too expensive to order 3 of them. I just ordered one which will arrive this week. My plan is to reproduce it twice to have one for every zone. I would be very happy to share my pinout (and maybe some gerber files for the pcbs) in the next few weeks. I read that others had issues bringing their setups to life with more than one sensor, but I will either way go with the standard controller first and try to replace it with this solution here later on when i have more free time. —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[rubenbe]

@haraldfunk multiple sensors should work, but only one per zone. I used to have to sensors in one zone (one on each fan) but I ruined one and didn't replace it due to exuberant the price.

There is no limitation in the software to only use one sensor per zone, the only thing is that it isn't tested (so is likely to contain a bug).

[Mariuccio112]

I did some test apparently this is the pinout for the i2c I tried to connect a sensor but , it was recognized but is giving me wrong reading temp 0C and 30% humidity always, so probably I’m still missing something or the sensor is not good.

image.png

[rubenbe]

That's great! Have you found the blinky LED connector? Maybe one of the SDA/SCL lines should actually be connected to the LED and that's the reason you get bad data (which is always the same)

[Mariuccio112]

How often does it blink, on the logic analyzer the o my two lines changing were the two that I used for the Ada and scl, all the other are fix at 3.3Il giorno 17 giu 2025, alle ore 13:40, rubenbe ***@***.***> ha scritto:rubenbe left a comment (rubenbe/comfospottwin40#14) That's great! Have you found the blinky LED connector? Maybe one of the SDA/SCL lines should actually be connected to the LED and that's the reason you get bad data (which is always the same) —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you authored the thread.Message ID: ***@***.***>

[rubenbe]

Hmm, you say something there. They might have wired the LED to the SDA or the SCL line to indicate I2C traffic. It does blink every few seconds which could be the same interval as it fetching the data. I have to get on the roof to get the sensor, but I'll do it one of these days.

[Mariuccio112]

I’m thinking that they could have installed some additional resistors on their board, with the scope of identify the board type or select a configuration, maybe they build a version of the board with other sensors brand as well. I’m thinking this because the other pins are kept at 3.3v but between them they have some resistance so seems are not just directly connected to the vcc rail

[rubenbe]

Hmm, very good point, I'll have a look to remove the broken sensor from my setup for closer inspection.