Problem with SHT10 and SHT30?

Hey guys,

I have a quick question for the Arduino's community about humidity sensors. My project is to measure humidity of the soil at different depth. In order to make sure numbers I see make sense, I measured humidity first in a dry soil, and then slowly increased humidity. I wait long enough to reach stability of the system. When I use the sensor V1.2, I have a pretty linear correlation from 0 to 100%, but when I use SHT10 or SHT30, it looks more like a logarithmic curve in which measurement saturates at 100% while humidity is only 5% in the soil. Is it normal? Is there something I'm doing wrong?
The program is very standard and I'm using libraries SHT1x-master (SHT1x/SHT1x.h at master · practicalarduino/SHT1x · GitHub) and SHT3x-master (SHT3x/SHT3x.h at master · Risele/SHT3x · GitHub)

Thank you so much in advance for your help
Laurent

The only thing that works for soil is capacitive sensors.

What is sensor V1.2 ?

Thank you for taking time to answer.

Interestingly, I realized the V1.2 is actually a capacitive sensor (https://store.qkits.com/capacitive-soil-moisture-sensor-v1-2.html).

Now, I need to read a bit more on that. It seems that these SHTs are not optimal for the soil then.

Thank you again
Laurent

Can you give a link or a photo of your SHT modules ?
The sensor itself is only for the Relative Humidity of air. Sometimes a special case is used to protect them from rain. However, putting them in soil is something else.

Did you pay too much ? NEW ! Capacitive soil moisture sensor not easy to corrode wide voltage wire for arduino|soil moisture sensor|moisture sensorcapacitive soil moisture sensor - AliExpress.

There are capacitive sensors with protection for the electronics. They can be put deeper in the soil.
You can also do that yourself. Search for capacitive soil sensor in combination with: "waterproof", "waterproofing", "ruggedized", "soilwatch 10", and so on.

Yes, I paid a bit more than the V1.2!!

But that's fine. Now I know at least what's wrong with my measurements with these SHTs. Thanks to you! I will try to recycle them for something else. I will follow your advice.

Thanks a lot

That is a very nice weatherproof casing. Putting them in soil is almost the same as putting them in water. In the long run they don't like that.

Can you open the casing to check if the sensor is not dirty ? Let it dry for a week and try to measure the air humidity.
I think the SHT30 is not protected.
Others can have a filter membrane or a protection cover: https://www.sensirion.com/en/environmental-sensors/humidity-sensors/digital-humidity-sensors-for-various-applications/.

Thanks a lot for that. I think that's what I need indeed.

After a quick search, it looks like the DHT35 could also work for me :

I will continue looking for other models.

Can you confirm that someone has used such a sensor in the soil and that it still works after a few years ?
Adafruit test what they sell, and they try to make a good selection of useful components.
There is a whole lot of bad rubbish out there. You can buy hundred things that promise a lot and none is okay.
Use capacitive sensors or else something from a well known brand.

I'm not sure if it was tested for that long. It's a good point that I have to check because it's important for us. Will check Adafruit.
Thanks!