Looking at the principles of operation of the Capacitive soil moisture sensor, testing its output in wet to dry conditions, and taking it out to the garden for a real soil test!

These sensors on Amazon (affiliate links):
Amazon.com: https://amzn.to/2LJ6kLS
Amazon.ca: https://amzn.to/2JnQDrV

Capacitive Sensor References:
Capacitive-Based Liquid Level Sensing Sensor Reference
Design
http://www.ti.com/lit/ug/tidu736a/tidu736a.pdf

The Fringe-Capacitance of Etching Holes for CMOS-MEMS
http://www.mdpi.com/2072-666X/6/11/1445/htm

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46 Comments

  3. is it possible to read the capacitance of the probe using dc out? I need that value for my program to work

  7. Have you tried if you see a difference after a few days? Once the water sets around the soil, I'm wondering if the values of "humid soil" actually work. Soil that you just watered is not the same a few hours later

  8. I got a couple of them, unfortunately only one works. The others all have a similar erratic behaviour. I double checked output Volages with Multimeter. So I know. 100% is 1.2V and 0% is 2.1V. now when i put the unit in water or in air, I get appropiate stable readings. But at the moment I put it into the earth it starts to act unpredictable, putting out instable Voltages between 3,5 and 1 Volts. I disconnect the Data from the A/D converter and measure output voltage and can confirm the strange output of the moisture sensor. Now i am thinking moisture and conductivity, so I enclosed the entire device including the now soldered on wires in epoxy, still have the same erratic behaiour when in earth. I am so tired of this shit.

  9. Thanks for this great video. I'm using one of these in my garden, connected to an ESP8266 but I am getting erratic values. Sometimes it is steady and decreasing just a little at a time, which is what I would expect. Other times it jumps up or down by 50%. If I move it just a little then it definitely changes big time. Any thoughts on how I can stabilize the readings?

  10. Don't forget the sensor is very non-linear. In my testing, it is much less sensitive in the top half, which is impractical.

  12. We built a circuit on the breadboard and measured the frequency. When we measured the frequency in front of the Cprobe, we had about 250 kHZ. For your information, we excluded the 3.3 regulator part. I'm worried because 370kHZ is not coming out. Please give me some advice if possible!

  14. Isn't it more important to get the reference values from actual dry and moist soil? The ratio of the dielectric constant of water/air is probably quite different than moist soil/dry soil. So for calibrating this using a micro controller, I would find some soil I define as dry, note the value, and water it to make a definition of moist. Then I'd use those values for the micro controller to determine when it's time to water the soil. Thank you very much for this explanation. I see that I've bought the crap kind of sensor, the electrolysis one with two prongs with exposed copper.

  16. Hi does anybody know what the serial output is related to? As in the values it gives on the datasheet of water being [360-260] etc?

  19. hi, how long does it take to get a reading? we'll need to know this when using it with a microcontroller. thx!

  24. hello, thanks for this video.

    I wanted to ask you if by chance you could explain to me more precisely the internal circuit of the sensor

  25. The output range in these things seems to change once you hook up a relay and pump. nice test btw, thanks.

  27. I usually see programmers using water and air as the 2 extremes (wet and dry) to calibrate the sensor, but that's not entirely correct. As far as I understood the capacitive sensor, it deppends on the conductivity of the medium in which it is inserted right? Pure water (or water with food colouring as well) has not a great conductivity, at least not as high as water + soil because of minerals. So while calibrating like this, you might see moisture levels in wet soil higher than pure water, which would be weird. Am I correct? (Sorry for bad english)

  29. Could you epoxy the whole sensor (components) to make it waterproof?
    Iow is epoxy harmful to the smd components?

  34. I just bought 10 of these and I was looking for a video to teach me about them. This was very helpful. Do you have a video on just the 555 chip?

  35. I looked into the datasheet of the IC and didn't understand how this works. Thanks for the explanation. This circuit design is really cheap, but effective. Amazing how people solve some problems 🙂

  38. Hi, will length /width of the cable influence readings from sensor? Typically you do not want to have electronics near to the soil, that is getting water. So if you place your measuring device (ESP, Arduino, RaspPi, etc) 10-15 meters away, there will be long cable. I am testing this sensor with ESP32 runnign Micropython, but so far do not get reliable result. My cable is about 3 meters long. Curiuos if anybody has this reliably working in their gardening projects.

  43. putting epoxy around the components and socket on top? And maybe a transparent heat shrinking tube, too…

  44. So if I were to use this for low powered applications, the 555 timer would drain the battery, no?

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