Capacitive Soil Moisture Sensor barely drops Values

Hi,

so I am using a capacitive Soil Moisture Sensor (it says v1.2 on it) to measure the soil moisture (obv) of soil inside a plant pot. The thing is, I had it running for a few days now and the values barely drop. The Soil is still at 100% moisture altought the soil feels very dry up top. Obviously the soil has more moisture if I dig down to where the Sensor sits but that will basically never change, the soil will always have some kind of moisture in it, at least if its inside (outside the sun might dry it to extrem levels). The Value it reads also depends strongly on how deep the Sensor is burried in the dirt.
456
The Sensor Values ranges from 730-80 (if its just in the air, depending on how dry the sensor is) to ~425 if it is submerged in water. Then, if it is Wet but in the Air (just taken out of a glass of water), the Sensor Reads 630 and that value rises which means it is drying and therefore working properly. But then again, putting it in the soil sets it at about 500 and I can bet that it will not change more than 5% in the next few days.

I tried calibrating the Sensor using % maps as follows:

int convertMoistureToPercent(int value){
  int MoisturePercentValue = 0;
  MoisturePercentValue = map(value, 700, 500, 0, 100);
  if(MoisturePercentValue > 100){
    MoisturePercentValue = 100;
  }

  return MoisturePercentValue;
}

I got these values by inserting the Sensor in a glass of completrly Dry soil (out of a bag of dirt) and in a glass of soil which has just been watered.
Now I changed the map to 700,400,0,100 and of course the reading changed to 61% but that won't move now.

Since this sensor is widely used, someone has to have an idea on how to properly calibrate the sensor for sure. Maybe I have done it wrong or maybe the soil really is still 61% wet and I am just too impatient. I could of course set the trigger to water it on something like 60%, depending on the plant but then it would take weeks to get back to 60%... did I map it wrong?

Thanks in advance!

Jan

Did you try to calibrate the sensor before using it as per below tutorial?

https://wiki.dfrobot.com/Capacitive_Soil_Moisture_Sensor_SKU_SEN0193

I experienced the exact same issue in the past. The sensor works perfectly when trying to test in a glass of water and in air. But it never works properly when inserted into the soil. From what I noticed, after watering the plant, moisture seems to cling onto the surface of the sensor, and the moisture can't seem to evaporate properly due to it being trapped under the soil. On various occasions, I noticed the soil has gone completely dry, but when I pull out the sensor, I can feel moisture on its surface when touching it.

At first, I have spent weeks trialing and error, using multiple different sensors to ensure it's not an issue with an individual sensor, and I also tried waterproofing the top part where the electronic components were, in case moisture was affecting it, but all did not work out for me. I have never found a solution, and have since given up, because my herbs need watering often in tropical weather. It will probably dry in the end, but I have never waited to try it out, as my plants would have been dead by then.

JanL:
Hi,

so I am using a capacitive Soil Moisture Sensor (it says v1.2 on it) to measure the soil moisture (obv) of soil inside a plant pot. The thing is, I had it running for a few days now and the values barely drop. The Soil is still at 100% moisture altought the soil feels very dry up top. Obviously the soil has more moisture if I dig down to where the Sensor sits but that will basically never change, the soil will always have some kind of moisture in it, at least if its inside (outside the sun might dry it to extrem levels). The Value it reads also depends strongly on how deep the Sensor is burried in the dirt.
456
The Sensor Values ranges from 730-80 (if its just in the air, depending on how dry the sensor is) to ~425 if it is submerged in water. Then, if it is Wet but in the Air (just taken out of a glass of water), the Sensor Reads 630 and that value rises which means it is drying and therefore working properly. But then again, putting it in the soil sets it at about 500 and I can bet that it will not change more than 5% in the next few days.

I tried calibrating the Sensor using % maps as follows:

int convertMoistureToPercent(int value){

int MoisturePercentValue = 0;
  MoisturePercentValue = map(value, 700, 500, 0, 100);
  if(MoisturePercentValue > 100){
    MoisturePercentValue = 100;
  }

return MoisturePercentValue;
}




I got these values by inserting the Sensor in a glass of completrly Dry soil (out of a bag of dirt) and in a glass of soil which has just been watered. 
Now I changed the map to 700,400,0,100 and of course the reading changed to 61% but that won't move now. 

Since this sensor is widely used, someone has to have an idea on how to properly calibrate the sensor for sure. Maybe I have done it wrong or maybe the soil really is still 61% wet and I am just too impatient. I could of course set the trigger to water it on something like 60%, depending on the plant but then it would take weeks to get back to 60%... did I map it wrong?

Thanks in advance!

Jan

Byork:
I experienced the exact same issue in the past. The sensor works perfectly when trying to test in a glass of water and in air. But it never works properly when inserted into the soil. From what I noticed, after watering the plant, moisture seems to cling onto the surface of the sensor, and the moisture can't seem to evaporate properly due to it being trapped under the soil. On various occasions, I noticed the soil has gone completely dry, but when I pull out the sensor, I can feel moisture on its surface when touching it.

At first, I have spent weeks trialing and error, using multiple different sensors to ensure it's not an issue with an individual sensor, and I also tried waterproofing the top part where the electronic components were, in case moisture was affecting it, but all did not work out for me. I have never found a solution, and have since given up, because my herbs need watering often in tropical weather. It will probably dry in the end, but I have never waited to try it out, as my plants would have been dead by then.

Hello, I have had the same problem few months ago. I am now thinking to buy professional industry grade waterproof soil moisture sensors like this one: Waterproof Soil Moisture Sensor VH400 2m cable Fast Response Time Arduino RPi | eBay.

I found 1 point in the description quite interesting: "Ignores the Salt in your Soil", this is not handled by generic soil moisture sensors I guess so.

It does not use exposed metal parts so no corrosion and also requires no calibration.

ryanwalkers:
professional industry grade waterproof soil moisture sensors

...and then you come with an eBay link, with description in Chinglish. Oh well, it's expensive so it must be good, right?

wvmarle:
...and then you come with an eBay link, with description in Chinglish. Oh well, it's expensive so it must be good, right?

I am sorry to disappoint you but that is worth the cost (i am using that sensor since years) and its made in USA not China. The original manufacturer is a USA based company called Vege.

that is worth the cost

How fascinating!

For thousands of years people have touched the soil of a potted plant with their fingers, and were able to determine whether watering is required.

But now, you can spend $100 for a sensor, more for the Arduino, display and computer to program the setup -- and this saves you a lot of money.

I do agree $100 is a bit exorbitant but I am vouching for the sensor, delivery within USA is $15 so if I remember I got it for around $70. That seems reasonable to me and its made in USA, so labor laws/cost and high shipping cost add up.

Chinese goods are good but not all of them are good.

Also there is no "state-sponsored" Yanwen, SunYou shippers in USA so international shipping is naturally high.

Anyways lets close this argument, there is a trade war going on to entertain us. I do use Chinese products ONLY when they work reliably. Have a good day! Cheers Mate

adam1986:
I am sorry to disappoint you but that is worth the cost (i am using that sensor since years) and its made in USA not China.

Good for you. I do hope you realise you sent a link to the venerable e-bay site, with a description in clear Chinglish (or did language standards really slip so badly in the USA?).

The manufacturer's site is less bad, yet within a few lines I found the first grammar error. At least they offer the sensors at a much less shocking price: less than USD 40.

wvmarle:
with a description in clear Chinglish (or did language standards really slip so badly in the USA?).

The manufacturer’s site is less bad, yet within a few lines I found the first grammar error.

How hypocritical and ironic!

If you judge someone’s technical prowess/ability based on their English grammar skills then by the same rule you should NOT buy Chinglish products (even South Korean products for that matter). That only proves you go for cheap products and not quality. Heard of DigiKey/Mouser? They have better support than Taobao/Aliexpress.

wvmarle:
At least they offer the sensors at a much less shocking price: less than USD 40.

Yes, that is what I said earlier.

USD 40 + USD 15 (domestic USA shipping)

USD 40 + USD 49 (International shipping)

Shipping charges add up, if you actually checkout after putting it into the cart. Unfortunately, USA does not have state backed Yanwen or SunYou or similar to save you on shipping cost.

@ryan & OP if you are interested, I would suggest you to ship to a “virtual USA address” and you could maybe save 10-15 USD? Dont know how that works but some of my non-USA friends use that.

adam1986:
How hypocritical and ironic!

If you judge someone's technical prowess/ability based on their English grammar skills then by the same rule you should NOT buy Chinglish products (even South Korean products for that matter). That only proves you go for cheap products and not quality. Heard of DigiKey/Mouser? They have better support than Taobao/Aliexpress.

Attention to detail is what matters. If a manufacturer of a purportedly high-end product doesn't care enough to get their web site done well, including the text in what is presumably their native language, that is an indication of lack of care for detail, which may also be reflected in the product. A South Korean manufacturer should have at least correct Korean on their site, and a Chinese manufacturer correct Chinese. Them caring enough to have their web site translated in correct English does mean a lot to me: it means they do care about detail.

Likewise I would not expect perfect Chinese or Korean on the web page of an American supplier (if they would even care to support any language other than English).

If I buy a cheap product off Taobao I have no expectations of any English description or support in the first place. Not even if I see English on a Chinese manufacturer's web site: it's not their native language, it's a translation. The Chinese I do expect to be grammatically correct but my Chinese is far from good enough to judge that.

Digikey's information on the web site is indeed much better than what you find at many Taobao shops, but also there I've ran into quite some inconsistencies when it comes to product specifications, with the info on the web site not matching the data sheet.

adam1986:
@ryan & OP if you are interested, I would suggest you to ship to a "virtual USA address" and you could maybe save 10-15 USD? Dont know how that works but some of my non-USA friends use that.

Thanks, but no Thanks. I found better soil moisture sensors that are far cheaper inclusive of shipping.

Also there are couple of combinations with moisture like temp, nutrients, EC (Electrical Conductivity) etc.

Wireless ESP8266 based with AA battery

Waterproof/Weatherproof just like yours but far more cheaper

Waterproof Soil Moisture + Electrical Conductivity (EC) + Temp Sensor All in 1 with USB Connector and Android App

Wireless ESP32 DHT12 Temp + Humidity with USB-C Connector

If you want the whole KIT

There is this Temp + Humidity + EC over here

Thanks for those… helpful comments.

adam1986:
I am sorry to disappoint you but that is worth the cost (i am using that sensor since years) and its made in USA not China. This is the original manufacturer (Soil Moisture Sensor - VH400).

This is acutally very interesting but sadly a bit out of my price range for a simple sensor…

Byork:
I experienced the exact same issue in the past. The sensor works perfectly when trying to test in a glass of water and in air. But it never works properly when inserted into the soil. From what I noticed, after watering the plant, moisture seems to cling onto the surface of the sensor, and the moisture can’t seem to evaporate properly due to it being trapped under the soil. On various occasions, I noticed the soil has gone completely dry, but when I pull out the sensor, I can feel moisture on its surface when touching it.

At first, I have spent weeks trialing and error, using multiple different sensors to ensure it’s not an issue with an individual sensor, and I also tried waterproofing the top part where the electronic components were, in case moisture was affecting it, but all did not work out for me. I have never found a solution, and have since given up, because my herbs need watering often in tropical weather. It will probably dry in the end, but I have never waited to try it out, as my plants would have been dead by then.

excatly what I am experiencing. I even upgraded my Sensor to a capacitive one but right now in Germany where I live we have 35-40 degree celcius and I was gone for a few days, didn’t water my plant for over a week at least. When I left a few days ago, it was at 66%, now I came back and it stayed there. I think its what you say: The sensor cannot dry in the dirt. The value will go up when watering but will take ages to drop in value if ever. Not really helpful :confused:

I’ve been using the SEN0193 for about a year and a half now. It is in my garden buried about 1 - 4 inches with resin epoxy covering the surface mount components. It seemed to work OK except when ground temperatures go below freezing. I’ve done rough verification from a university sensor 1 county away. After about a year probably a running squirrel caught the wire and somewhat dislodged it. Subsequently re-buried it but then it was stuck at ~95%. ***Removed and found board coating on non-sensor trace side had failed - appeared to retain water. I blow dried the board, confirmed dry air number, added more 5 minute epoxy around components, sides of pcb, and back side of sensor traces - hopefully to assure no more board water penetration. It seems OK now (~5 months) but does appear to be temperature sensitive. it is buried in soil with full sun - attaching recent graph history. My experience - the SEN0193 kindof works but can be susceptible to water damage due to board coating failure. Thanks to previous posters on potential alternatives! My SEN0193 github project - GitHub - mrcodegh/SoilSensor_ESP12f: Soil temperature and moisture reporting using ESP8266 12f