How to glow led bulb at a distance using arduino

Ultrasonic sensor comes very handy for small projects. It can be used for making radar, measuring distance, different types of  alarm system. You can download ultrasonic sensor HC-SR04 datasheet. Arduino connection with ultrasonic sensor is shown in picture.

void setup()

{

  pinMode(12,OUTPUT);//pin for trigger

  pinMode(11,OUTPUT);//output for led bulb

  pinMode(13,INPUT);//pin for echo

  Serial.begin(9600);

}

void loop()

{

  digitalWrite(12,HIGH);

  delayMicroseconds(30);

  digitalWrite(12,LOW);

  delayMicroseconds(2);

  int a=pulseIn(13,HIGH);//gives time after which high pulse is coming

  int d=(a*0.034)/2;//342 is the speed of sound

  Serial.print(d);//print on serial monitor

  Serial.println(" cm");

  delay(50);

  if(d==50)

  {

    digitalWrite(11,HIGH);//glows led

  }

  else

  {

    digitalWrite(11,LOW);

  } 

}

You can set range for led bulb to work.

Example: 

if(d>=50&&d<=100)

  {

    digitalWrite(11,HIGH);//glows led

  }

 if(d>=1&&d<=49)

  {

    digitalWrite(11,LOW);

  }