Soil Moisture Sensor Module

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Soil Moisture Sensor Module can be used to detect the moisture of the soil or judge if there is water around the sensor. It has both analog and digital outputs. We can vary the digital output sensitivity of this module using a potentiometer and the sensor is based upon resistance.

Soil moisture sensor consists of two conducting plates which function as a probe and acting as a variable resistor together. They are used to measure the volumetric content of water. The two probes allow the current to pass through the soil, which gives the resistance value to measure the moisture value. When the sensor is inserted into the water, the resistance will decrease and get better conductivity between plates. Dry soil conducts electricity poorly, so when there is less water, then the soil will conduct less electricity, which means that there will be more resistance.

Pin Configuration

Pin Description
VCC The VCC pin powers the module, typically with +5V
GND Power Supply Ground
DO Digital Out Pin for Digital Output
 AO Analog out Pin for Analog Output


The working of the Soil Moisture Sensor is very simple. It works on the principle of voltage comparison. Moisture sensor module consists of four pins i.e. VCC, GND, DO, AO. Digital out pin is connected to the output pin of LM393 comparator IC while the analog pin is connected to Moisture sensor. The internal Circuit diagram of the Moisture sensor module is given below.

Operating voltage 3.3v - 5 V
Sensing probe dimensions 60x30mm
Panel PCB dimensions 30 x 60mm
Analog Output 0-5 V
Digital Output 0 or 5 V

Q1. Can soil moisture sensor be placed in water? How to test soil moisture sensor?
Ans. Yes, one can place soil moisture sensor in water, i.e. the conducting plates which we also call probes. But it is of no use. If you want to use soil moisture sensor for watering the plants, proper readings is required. Positioning of the sensor should be correct. When we place soil moisture sensor in the water, we get readings ranging from 150-283 on the serial monitor, in dry soil we get 1015-1020 and in wet soil we get 236-300. It varies depending upon the moisture content in the soil. You can observe/test that on serial monitor by interfacing the sensor with Arduino/Node MCU.

Q2. Can soil moisture sensor be used as pH sensor?
Ans. No, you cannot use soil moisture sensor as the pH sensor.

Q3. What is the output of soil moisture sensor?
Ans. The sensor is equipped with both analog and digital output, so it can be used in both analog and digital mode. Digital output can be 0 or VCC i.e. HIGH or LOW whereas analog outputs don’t have to be 0 or VCC, they can be in between them.

Q4. How to set threshold value in soil moisture sensor?
Ans. You can use the potentiometer dial on the sensor for setting the threshold value. Another way is that just take the readings from the serial monitor by varying the water content of the soil and alter the if condition in the program accordingly.

Q5. Can humidity sensor be used as moisture sensor in soil?
Ans. No, you cannot use humidity sensor as moisture sensor in soil. It should be placed in a sheltered area that is protected from water; otherwise, it will get damaged.

Q6. What is the range of soil moisture sensor?
Ans. You are provided with a potentiometer dial on the soil moisture sensor which you can adjust to set the reference voltage in case you are using D0 pin of the sensor. Digital output can be 0 or VCC i.e. HIGH or LOW whereas if you are using A0 pin of the sensor then the analog outputs can be 0V to 5V. The ADC on the Arduino is a 10-bit ADC which converts analog voltages into digital values.

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