const int trigPin = 9;
const int echoPin = 10;
const int relayPin = 8;

long duration;
float distance;

float maxLevel = 10.0; // in cm (distance from sensor to top of dam water)
float minLevel = 50.0; // in cm (safe water level)

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, LOW); // relay OFF initially
}

void loop() {
  // Send ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Measure pulse duration
  duration = pulseIn(echoPin, HIGH);

  // Calculate distance in cm
  distance = duration * 0.034 / 2;

  Serial.print("Water Level Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Control gate based on water level
  if (distance <= maxLevel) {
    Serial.println("⚠ High Water Level! Opening Dam Gate...");
    digitalWrite(relayPin, HIGH); // turn ON motor or open gate
  } 
  else if (distance > maxLevel && distance <= minLevel) {
    Serial.println("✅ Water Level Normal. Gate Closed.");
    digitalWrite(relayPin, LOW); // turn OFF motor or close gate
  } 
  else {
    Serial.println("Water Level Low.");
    digitalWrite(relayPin, LOW);
  }

  delay(2000); // check every 2 seconds
}