Introduction

Soil Moisture Sensor

Soil moisture is basically the content of water present in soil. This can be measured using a soil moisture sensor which consists of two conducting probes that act as a probe. It can measure the moisture content in the soil based on the change in resistance between the two conducting plates.

The resistance between the two conducting plates varies in an inverse manner with the amount of moisture present in the soil.

For more information about soil moisture sensor and how to use it, refer the topic Soil Moisture Sensor in the sensors and modules section.

Interfacing Diagram

Interfacing Soil Moisture Sensor with Particle Photon

Example

Measuring soil moisture in terms of percentage.

Here, the analog output of soil moisture sensor is processed using ADC. The moisture content in terms of percentage is displayed on the serial monitor.

The output of the soil moisture sensor changes in the range of ADC value from 0 to 4095.

This can be represented as moisture value in terms of percentage using formula given below.

Analog output  =  ADC value / 4095

Moisture in percentage = 100 – (Analog output * 100)

For zero moisture, we get maximum value of 12-bit ADC, i.e. 4095. This in turn gives 0% moisture.

Sketch

const int sensor_pin = A4;	/* Soil moisture sensor O/P pin */

void setup() {
  Serial.begin(9600);	/* Define baud rate for serial communication */
}

void loop() {
  float moisture_percentage;
  int sensor_analog;
  sensor_analog = analogRead(sensor_pin);
  moisture_percentage = (100 - ( (sensor_analog/4095.00) * 100 ) );
  Serial.print("Moisture Percentage = ");
  Serial.print(moisture_percentage);
  Serial.print("%\n\n");
  delay(1000);
}