Soil Moisture Sensor Working and Applications

What is a Soil Moisture Sensor?

Soil water content has important effects on many fundamental biophysical processes. It influences seed germination, plant growth and nutrition, microbial degradation of soil organic matter, conversion of nutrients in the root zone, and water transfer at the land-air interface. Quantification of soil water content is necessary for a variety of applications ranging from large-scale calibration of global climate models to field monitoring in agricultural and horticultural systems. When we need to measure water content in the soil, the soil moisture sensor comes to mind.


A soil moisture sensor is a type of sensor used to measure the volumetric water content of the soil. Because, a direct gravimetric amount of soil moisture must be removed, dried and weighed. These sensors do not directly measure volumetric water content using other soil laws such as permittivity, electrical resistivity, interaction with neutrons, and water content displacement. 


 The relationship between calculated properties and soil moisture needs to be adjusted and can change with ecological factors such as temperature, soil type and other conductivity. Reflected microwave radiation can be affected by soil moisture and is mainly used in remote sensing in agriculture and hydrology.

What is a soil moisture sensor

The main advantage of using soil moisture sensors to plan irrigation is more efficient water usage, thus reducing water consumption while allowing plant roots to grow deeper and avoiding over-watering or over-watering. Nutrient leaching is avoided. Avoiding overwatering also eliminates favorable conditions for some pests and fungal diseases. These statements are especially true for trees affected by citrus blight. This is because reduced root size and function can exacerbate the effects of drought.

Working Principle and Specification

This sensor primarily uses capacitance to measure soil moisture content (permittivity). The functionality of this sensor can be performed by inserting this sensor into the soil and reporting the moisture content status of the soil in percentage. This sensor is ideal for conducting experiments in science courses such as environmental science, agriculture, biology, soil science, botany and horticulture.


This soil moisture sensor is integrated with the LM393 comparator chip, this is an integrated circuit (IC), a dual differential comparator, consisting of two integrated operational amplifiers. They are commonly used in devices that measure analog signals and act as Analog-to-digital converters (ADC) also each comparator accepts two inputs for comparison. A comparator compares these two input voltages, measures which input voltage is greater, and provides an output. 

soil moisture sensor

This module has a built-in potentiometer to set the sensitivity of the digital output (DO). You can set the threshold with a potentiometer. So when the moisture level exceeds the threshold, the module will output LOW, otherwise, it will output HIGH. This setting is very useful for triggering actions when certain thresholds are reached. For example, when the soil moisture level exceeds a threshold,  a relay can be activated to start pumping water.


  • It is integrated with the LM393 comparator module chip.
  • Dual output module, analog and digital¬†
  • The soil moisture sensor have to fix bolt holes for easy mounting.¬†
  • There are two LED indicators, red (power indicator) and green (output indicator).¬†
  • Soil moisture sensors are the most sensitive to the environment and typically use soil moisture content.


Sensor Type

Soil Moisture sensor

Operating voltage

3.3 V - 5V

Current flow

< 20 Am

Type of Interface

Analog Type

Working temperature of the sensor

10 - 30 degree Celcius

PCB Dimension of comparator

3 cm x 1.5 cm

Soil Probe Dimension

6 cm x 3 cm

Cable length

20 cm


50 gms

Pin Configuration:

pin configuration of soil moisture sensor

Sensor Probe


Voltage supply


-ve pin

LM393 Comparator


Power supply


Common GND


Analog pin


Digital pin

Interface Arduino with the Soil Moisture Sensor:

Interface Arduino with the Soil moisture sensor



LM393 comparator








GPIO pins (9)


#define sensor_pin 9

void setup() {



void loop() {

  int val;


//val=analogRead(A0); //If you connect analog pin




Benefits of Soil Moisture Sensor

  • Less water use can be modified to lower and higher thresholds to preserve ideal soil moisture saturation and reduce plant withering.¬†
  • It can result in deeper plant root growth, decreased soil runoff and leaching, and unfavorable circumstances for pests and fungi.


  • Agriculture
  • Landscape irrigation
  • Research
  • Simple sensors for gardeners

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