// Defines pin numbers
const int ledPin  = A3;
const int trigPin = 5;
const int echoPin = 4;

// Defines variables
long duration;
int distance;
int safetyDistance;

void setup() {
  pinMode(trigPin,OUTPUT);
  pinMode(echoPin,INPUT);
  pinMode(ledPin,OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Clears the trigPin
  digitalWrite(trigPin,LOW);
  delayMicroseconds(2);
  
  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin,HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin,LOW);
 
  // Reads the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin,HIGH);
  
  // Calculating the distance
  distance = duration*0.034/2;
  
  safetyDistance = distance;
  if (safetyDistance <= 15) {
    digitalWrite(ledPin,HIGH);
  }
  
  else {
    digitalWrite(ledPin,LOW);
  }
  
  // Prints the distance on the Serial Monitor
  Serial.print("Distance: ");
  Serial.println(distance);
}