Measure soil Moisture with Arduino – Gardening

Needed Hardware

Arduino Uno

Price: less than $30 (Amazon)

A moisture sensor
Price: less than $7 (Amazon)

Simple Way to connect to the Arduino

code

int sensorPin = 0;    // select the input pin for the potentiometer
int sensorValue = 0;  // variable to store the value coming from the sensor
 
void setup() {
  // declare the ledPin as an OUTPUT:
   Serial.begin(9600);  
}
 
void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);    
  delay(1000);          
  Serial.print("sensor = " );                       
  Serial.println(sensorValue);                   
}

Output

Sensot in air: value = 0

sensor = 0 sensor = 0 sensor = 0 sensor = 0

Sensor in dry soil:  0 < value  < 300

sensor = 35 sensor = 41 sensor = 38 sensor = 49

Sensor in humid soil: 300 < value < 700

sensor = 578 sensor = 576 sensor = 582 sensor = 589

Sensor in water: value > 700

sensor = 934 sensor = 940 sensor = 938 sensor = 940

Drawbacks

Using this sensor on this way always makes current cross over the sensor. It can cause corrosion across the probes.

Solutions:

• Do not left in place the sensor.
• Stop to power the sensor when is not used (see below)

Keep your sensor alive for a while

Here the aim is to stop to power the sensor when it is not used. Let says we want to get a value each 1min.

Code

int sensorPin = 0;    // select the input pin for the potentiometer
int sensorValue = 0;  // variable to store the value coming from the sensor
 
int sensorVCC = 13;
 
void setup() {
  // declare the ledPin as an OUTPUT:
   Serial.begin(9600);  
   pinMode(sensorVCC, OUTPUT); 
   digitalWrite(sensorVCC, LOW);
}
 
void loop() {
  // power the sensor
  digitalWrite(sensorVCC, HIGH);
  delay(100); //make sure the sensor is powered
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin); 
  //stop power 
  digitalWrite(sensorVCC, LOW);  
  //wait
  delay(60*1000);          
  Serial.print("sensor = " );                       
  Serial.println(sensorValue);                   
}

 Perspectives

This kind of sensor can be used to check plant watering or to auto water a plant.