It is a simple sensor that measures soil moisture by the variation of its conductivity. It is not accurate enough to make an absolute measurement of soil moisture, but it is not necessary to control an irrigation system either.

 

In my case the values obtained go from 0 submerged in water, to 4095 in the air (or in a very dry soil). A slightly moist soil would give typical values of 2400-2800. A dry soil will have values of 3200-4095.

 

With some Boolean logic, taking as reference the threshold triggers of the sensor, we can activate the irrigation pump including the hysteresis of the application.