At this point, we have connected the humidity sensor to the Arduino. Keep a pot of soil handy to test our humidity measuring system:

/* Gardening system
 * Lets water our plants on time
 */

// humidity sensor is at analog port 0
const in SENSOR_PORT = A0;

int sensorValue = 0;

void setup() {
  // We will initialize the serial port so we can print humidity data to the serial port.
  Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
  // Read the input on analog pin 0:
  sensorValue = analogRead(SENSOR_PORT);
  // A well watered soil will give a reading of atleast 380 to 400, a fully moist soil will have reading of 1023.
  sensorValue = constrain(sensorValue, 400, 1023);
  // We will reverse the range so that we get a rough humidity percentage reading i.e. 
  // fully moist soil will give a reading of 100% for 100% humidity and 
  // dry soil will read 0% for 0% humidity
  sensorValue = map(sensorValue,400,1023,100,0);

  // Print humidity value
  Serial.println(sensorValue);
  
  if (sensorValue >= 20) {
    Serial.println("soil is wet");
  } else
  {
    Serial.println("soil is dry");
  }

  delay(1000);
}

Upload the sketch to Arduino and start reading the serial port using the Arduino IDE by pressing .

Start placing the soil sensor in soil samples with different moisture levels. You should see the different humidity levels on the serial port monitor between 0 to 100.

Next we will set up the rest of our gardening system.