Watering system using Arduino, soil humidity sensor and 3-6V water pump. Checking for humidity is done every 24 hours.

wateringSystem.ino

const int sensorPin = A0;
const int sensorPowerPin = 4;
int sensorValue = 0;

const int transistorPin = 5;

const long sleepTime = 86390000; // 24 hours - 10 seconds
const int wateringTime = 10000; // 10 seconds

const int drySoil = 400;
const int wetSoil = 500;

void setup() {
  pinMode(sensorPowerPin, OUTPUT);
  pinMode(transistorPin, OUTPUT);   
}

void loop() {
  // read the value from the sensor:
  sensorValue = getSensorValue();
  if (sensorValue < wetSoil) {
     waterIt();
  } 
  delay(sleepTime);                  
}

int getSensorValue() {
   digitalWrite(sensorPowerPin, HIGH);
   int sensorValueTemp = analogRead(sensorPin);
   digitalWrite(sensorPowerPin, LOW);
   return sensorValueTemp;
}

void waterIt() {
  digitalWrite(transistorPin, HIGH); 
  delay(wateringTime);
  digitalWrite(transistorPin, LOW); 
}