// Define pins for HC-SR04 sensor
const int trigPin = 9;
const int echoPin = 10;

// Define pin for relay controlling the solenoid valve
const int relayPin = 8;

// Variables to store distance measurements
long duration;
int distance;

// Define water level thresholds in centimeters
int lowLevelThreshold = 15;  // Below this distance, the water level is low (solenoid opens)
int highLevelThreshold = 5;  // Above this distance, the water level is high (solenoid closes)

void setup() {
  // Set the trigger and echo pins as output and input
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  
  // Set the relay pin as output
  pinMode(relayPin, OUTPUT);
  
  // Initially, close the solenoid valve (turn relay off)
  digitalWrite(relayPin, LOW);
  
  // Begin serial communication for debugging
  Serial.begin(9600);
}

void loop() {
  // Clear the trigPin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send a 10us pulse to trigger the sensor
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Read the echoPin, and calculate the duration
  duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in centimeters (speed of sound = 0.034 cm/us)
  distance = duration * 0.034 / 2;

  // Print the distance to the serial monitor for debugging
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  // Check the water level and operate the solenoid valve accordingly
  
  // If the distance is greater than the low level threshold, open the valve (water level low)
  if (distance > lowLevelThreshold) {
    digitalWrite(relayPin, HIGH);  // Turn on the relay to open the solenoid valve
    Serial.println("Water level low. Opening valve...");
  }
  // If the distance is below the high level threshold, close the valve (water level high)
  else if (distance < highLevelThreshold) {
    digitalWrite(relayPin, LOW);   // Turn off the relay to close the solenoid valve
    Serial.println("Water level high. Closing valve...");
  }
  
  // Delay for 1 second before the next reading
  delay(1000);
}