/*
* Ultrasonic Sensor HC-SR04 and Arduino Tutorial
*/
	// defines pins numbers
const int trigPin = 17;
const int echoPin = 16;
const int buzzer = 2;
	// defines variables
long duration;
int distance;

void setup() 
{
pinMode(trigPin, OUTPUT); 	// Sets the trigPin as an Output
pinMode(echoPin, INPUT); 	// Sets the echoPin as an Input
Serial.begin(9600); 		// Starts the serial communication
}
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 microsec.
duration = pulseIn(echoPin, HIGH);
	// Calculating the distance
distance= ((duration*0.034)/2);
	// Prints the distance on the Serial Monitor
	if(distance <  100)
	{
		tone(buzzer,10000);
		delay(100);
		noTone(buzzer);
		delay(100);

	}
Serial.print("Distance: ");
Serial.print(distance);
Serial.println("cm");
delay(500);  //500 m.sec = 0.5 sec
}