#define TRIGGER_PIN 12
#define ECHO_PIN 13
#define LED_PIN 2
#define BUZZER 6
void setup() {
  Serial.begin(9600); //Initialize serial communication
  pinMode(TRIGGER_PIN,OUTPUT); //set trigger pin as output
  pinMode(ECHO_PIN,INPUT);  //set echo pin as input
  pinMode(LED_PIN,OUTPUT);  //set Led pin as output
  pinMode(BUZZER,OUTPUT);
}

void loop() {
  long duration,distance; //Variables to hold the pulse duration and calculated distance
  //Trigger ultrasonnic sensor
  digitalWrite(TRIGGER_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIGGER_PIN,HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIGGER_PIN,LOW);
  //Measure the pulse duratiob from the echo pin
  duration= pulseIn(ECHO_PIN,HIGH);
  //Calculate distance in centimeters
  distance =duration*0.0343/2;
  // print distance to serial monitor
  Serial.print("Distance:");
  Serial.print(distance);
  Serial.print("cm");
  // If distance is less than or equal to 20cm, turn on the LED;otherwise,turn it off
  if(distance<=20)
  {
    digitalWrite(LED_PIN,HIGH);
  }else{
    digitalWrite(LED_PIN,LOW);
    if(distance>20 && distance<=100){
      digitalWrite(BUZZER,HIGH);
    }else{
      digitalWrite(BUZZER,LOW);
    }
  }
  
}