Automatic Plant Watering

Steps

1. Wire the sensor

   Soil sensor AO to A0, VCC to 5V, GND to GND.

2. Wire the relay

   Relay IN to D7, VCC to 5V, GND to GND. Run the pump supply through the relay COM and NO terminals.

3. Calibrate

   Print analogRead(A0) to the Serial Monitor with the probe in dry and wet soil and set DRY between the two readings.

Code

const int SOIL = A0, RELAY = 7;
const int DRY = 600;                 // calibrate: higher reading = drier soil (typical resistive probe)

void setup() {
  pinMode(RELAY, OUTPUT);
  digitalWrite(RELAY, HIGH);         // HIGH = relay OFF on most active-LOW relay boards
}

void loop() {
  if (analogRead(SOIL) > DRY) {
    digitalWrite(RELAY, LOW);  delay(5000);    // pump on for 5 s
    digitalWrite(RELAY, HIGH); delay(60000);   // let the water soak in
  } else {
    delay(1000);
  }
}