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* all the sensors below are designed and manufactured by me (UL7AAjr)

Very first moisture sensor. Resistive.

resistive soil moisture sensorresistive soil moisture sensor

The construction of resistive sensors is not promising in the development of soil moisture sensors. Despite the fact that they are widely represented in the world market, such sensors are not stable and reliable in measurements. The corrosion of the electrodes and the dependence of the values on the acid-base composition of the soil make them practically useless in actual use.

Despite the simplicity of this sensor, it is critically different from similar resistive sensors. Since the electric resistance of the soil to the alternating current was measured. While similar sensors with electrodes of U-type make measurements of resistance to a direct current.

  

 

 

Inductive soil moisture sensor

inductive soil moisture sensorinductive soil moisture sensor

Inductive soil moisture sensors are more successful than resistive sensors. Based on the effect of dielectric permittivity on the quality factor of the inductor, such sensors can be electrically isolated from the soil. Can be used for reliable measurements of soil moisture. The disadvantage is the complexity of the circuitry for determining the quality factor of the inductor.

 

 

 

 

 

 

 

Capacitive soil moisture sensor.

Capacitive soil moisture sensorCapacitive soil moisture sensor

The most simple and reliable solution for measuring soil moisture is the use of capacitive sensors. The principle of measurement is based on a change in the capacitance of the capacitor, depending on the permittivity of the environment in which the capacitor plates are located. Such sensors are electrically isolated from the soil and their measurement values are reliable and stable.

 

 

 

The simplest way to measure capacitance without using a lot of analog components is to use a microcontroller. In this case, the sensors can be very compact and simple.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Using energy-saving microcontrollers, allow to create wireless sensors on battery power. 

 

 

 

 

 

 

 

 

 

 

Due to the compact design of capacitive sensors it is not difficult to create multi-channel instruments capable of measuring moisture values at different depths of the soil.

 

 

 

 

 

 

 

 

 

Multichannel sensors are also convenient if necessary to cover a large volume of soil. This is important when the sensor is used in a vegetable garden or a greenhouse. In this case, it is possible to measure soil moisture by discarding the minimum and maximum channel values. That allows you to get the actual value. 

 

 

 

 

 

 

 

 

 

To control soil moisture in plant pots, very compact capacitive sensors can be used.

 

 

 

 

 

 

 

 

Another option for sensors for indoor plants is the use of sensors with flexible electrodes, which can be placed along the wall of the pot.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After many years of experimentation and testing of various sensor designs, I was able to create a universal soil moisture sensor, which is excellent for indoor plants and for outdoor use. Now I'm working on an improved version of the sensor, capable of producing additional measurements of soil parameters.  New sensors models can be found in featured page.