#include <SoftwareSerial.h>

int buzzerPin = 8;           // Pin number the buzzer is connected
int echoPin = 11;            // Echo Pin of the ultrasonic sensor
int trigPin = 12;            // Trigger Pin of the ultrasonic sensor
unsigned long previousMillis = 0;   // Store the previous trigger time for buzzer
int maxBeepInterval = 1000; // Max beep interval
int minBeepInterval = 300;   // Min beep interval
int frequency = 1000;        // Buzzer frequency in Hz
float distance;              // Distance of the object from sensor
long echoTime;               // Time taken for the echo
int triggerAlarmDistance = 40;  // Buzzer will be triggered if the distance is less than this value (cm)
const int ledPin = 13;
long duration;

void setup() {
  pinMode(buzzerPin, OUTPUT);   // Set pin modes
  pinMode(echoPin, INPUT);
  pinMode(trigPin, OUTPUT);
  Serial.begin(9600); 
  pinMode(ledPin, OUTPUT);     // Initialize serial communication
}

void loop() {
  {
  digitalWrite(trigPin, LOW);                 // Set the trigger pin of the SR04 sensor to low
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);                // Send a pulse
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);                 // Set the trigger pin low

  echoTime = pulseIn(echoPin, HIGH);          // Measure echo time
  distance = echoTime * 0.0340 / 2;           // Calculate distance

  if (distance < triggerAlarmDistance) {      // If object is within trigger distance
    unsigned long currentMillis = millis();
    int val = map(distance, 2, triggerAlarmDistance, minBeepInterval, maxBeepInterval);  // Map distance to beep interval

    Serial.println("Sent SMS!");
    Serial.println("Dustbin is at maximum level");

    if (currentMillis - previousMillis >= val) {   // Check if it's time to trigger the buzzer
      tone(buzzerPin, frequency, val * 0.75);      // Trigger the buzzer
      previousMillis = currentMillis;              // Save current time
    }
  }
  delay(6000);  // Delay before next 
}
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = 0.034 * (duration / 2);

  if (distance < 27)
  {
    digitalWrite(ledPin, HIGH);
    delay(1000);
  }
  else 
  {
    digitalWrite(ledPin, LOW);
  }
  delay(300);
}