const int trigPin = 7; // Trigger Pin of Ultrasonic Sensor
const int echoPin = 6; // Echo Pin of Ultrasonic Sensor
const int ledPin = ; // LED Pin
const int buzzPin = ; // Buzzer Pin


void setup() {
   Serial.begin(9600); // Starting Serial Terminal
   pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
   pinMode(echoPin, INPUT); // Sets the echoPin as an Input
   pinMode(ledPin, OUTPUT); //Sets the LED pin as O/P
   pinMode(buzzPin, OUTPUT); //Sets the buzzer pin as O/P
}

void loop() {
   long duration,cm;
   digitalWrite(trigPin, LOW);
   delayMicroseconds(2);

   digitalWrite(trigPin, HIGH);
   delayMicroseconds(10);
   digitalWrite(pingPin, LOW);

   duration = pulseIn(echoPin, HIGH);
   cm = microsecondsToCentimeters(duration);

   Serial.print(cm);
   Serial.print("cm");
   Serial.println();
   if ( cm < 20.0 )
   {
      // TURN ON LED
	  digitalWrite(ledPin, HIGH);
      if ( cm < 10.0 )
	  {
	      // TURN ON Buzzer
		  tone(buzzPin, 1000);
		  delay(250)
	  }
	  else
	  {
		  // TURN OFF Buzzer
		  noTone(buzzPin);
		  delay(250);
	  }
   }
   else
   {
	  // TURN OFF
	  digitalWrite(ledPin, LOW);

   }
   delay(100);
}

long microsecondsToCentimeters(long microseconds) {
   return microseconds / 29 / 2;
}