/* This simple project describes how to make an ultrasonic alarm system using 
LED, Ultasonic Sensor(HC-SR04) and a buzzer.*/ 

//Firstly the connections of ultrasonic Sensor.Connect +5v and GND normally and trigger pin to 12 & echo pin to 13. 

#define trigPin 3
#define echoPin 2
int Buzzer = 12; // Connect buzzer pin to 8
int ledPin= 1;  //Connect LEd pin to 6
int duration, distance; //to measure the distance and time taken 

void setup() {
Serial.begin (9600); 
//Define the output and input objects(devices)
pinMode(trigPin, OUTPUT); 
pinMode(echoPin, INPUT);
pinMode(Buzzer, OUTPUT);
pinMode(ledPin, OUTPUT);
}

void loop() {

digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distance = (duration/2) / 29.1;
//when distance is greater than or equal to 200 OR less than or equal to 0,the buzzer and LED are off
if (distance >= 100 || distance <= 0) 
{
Serial.println("no object detected");
digitalWrite(Buzzer,LOW);
digitalWrite(ledPin,LOW);
noTone (12);
}
else {
Serial.println("object detected \n");
Serial.print("distance= ");              
Serial.print(distance);        //prints the distance if it is between the range 0 to 200
tone(Buzzer,400);              // play tone of 400Hz for 500 ms
digitalWrite(ledPin,HIGH);
}
}