Therefore moisture will eventually leak in and basically turn the capacitor into a resistor that will rot away. It has some other issues though: The coating that is used to cover the plates of the ‘capacitor’ sadly does not cover the sides of the PCB. That means that there is no need to have any bare metal sticking in the soil and therefore electrolysis is not a problem. That means it does not measure the resistance of the soil but the capacitance of the soil. However, it is definitely useable in combination with some solutions i will suggest later. My experience with it is not long enough to say if that is true, but it seems to be fake in that aspect. The above sensor supposedly is made from a non-electrolytic sensitive material. Also, because of the exposed electronics on it, it is not really suitable for outside use. It does not have a digital output, just an analog. It is also a resistive sensor and thus has the same problems as the one above. I suggest you do not use this sensor at all. That means that if you only use the Analog Output, you do not need the module at all, just connecting the sensor to an analog input and use an internal or external pullup will suffice. The analog output (AO) on the other hand is directly connected to the sensor. It is basically a comparator that when the soil moisture (and thus the resistance) reaches a value that is set with the variable resistor, the output of the comparator (DO) toggles. The image shows the circuit used in the module. Let me explain with help of a picture: Soil moisture sensor module The fact that there is a constant current flowing through the sensor when it is in contact with wet soil will lead to electrolytic breakdown of the very thin layer on the sensor’s PCB, or in other words: after a relatively short period the metal will no longer be on your sensor, but in your soil.Īnother issue with this module is that people use the entire module even when that is not necessary. It is a resistive soil moisture sensor and those come with a big problem: electrolysis. The above sensor is very popular, but in short: it is shit. I will discuss a few and come with ‘solutions’ to some of the biggest problems. There are a number of cheap sensors available in the various ‘Chinese webshops’ but those come with a caveat. want to monitor or automatically irrigate their plants. Soil moisture sensors are popular among hobbyists who e.g.
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