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

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

#define trigPin 12
#define echoPin 13
int Buzzer = 8; // Connect the buzzer pin to 8
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);
}

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 is off
 
if (distance >= 200 || distance <= 0) { 
  Serial.println("No object detected"); 
  digitalWrite(Buzzer, LOW);
 } 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 a tone of 400Hz
 }
}