#define trigger_pin 2
#define echo_pin 3
#define buzzer_pin 13
void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(trigger_pin, OUTPUT);
  pinMode(echo_pin, INPUT);
  pinMode(buzzer_pin, OUTPUT);

}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(trigger_pin, LOW);
  delay(200);
  digitalWrite(trigger_pin, HIGH);
  delay(200);
  digitalWrite(trigger_pin, LOW);

  long duration = pulseIn(echo_pin,HIGH);
  float distance = (duration/2.0)*0.0343;
  if(distance>=2 && distance <=40)
  {
    Serial.print("Distance: ");
    Serial.print(distance);
    Serial.print("cm");

  }
  else{
    Serial.println("Error out of range ");
    delay(500);
  } 
  if(distance >=20)
  {
    digitalWrite(buzzer_pin, HIGH);
  }
  else
  {
    digitalWrite(buzzer_pin, LOW);
  }

}