// ultrasonic sensor code

// declaring vairable for duration and distance
float distance;
float duration;

void setup() {
  // begins serail communication with the baud rate of 9600 bits
  Serial.begin(9600);

  // trig pin(triggers the ultrasonic sensor to throw waves)
  pinMode(18, OUTPUT);
  //echo pin(a singal is sent to the arduino if any obstruction is found in the waves)
  pinMode(17, INPUT);
  // led
  pinMode(4, OUTPUT);
}

void loop() {
  digitalWrite(18, HIGH);
  delay(10); // wait for 10 microseconds
  digitalWrite(18, LOW);

  // calculates the duration of the wave after obstruction
  duration = pulseIn(17, HIGH);
  
  // calculates the distance between the object that obstructed and the sensor
  distance = duration * 0.017;

  if(distance < 50)
  {
    digitalWrite(4, HIGH); // if distance is lower that 50, led is turned on
  }
  else
  {
    digitalWrite(4, LOW); // if distance is higher than 50, led is turned off
  }

  // prints the distance
  Serial.print("distance: ");
  Serial.print(distance);
  Serial.print(" cm");

}