int LED=2;
int trig=8;
int echo=10;
int distance;
int duration;
void setup()
{
  pinMode(trig,OUTPUT);
  pinMode(echo, INPUT);
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
}
void loop()
{
  digitalWrite(trig,LOW);
  delayMicroseconds(2);
   //Send ultrasonic pulse
  digitalWrite(trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig,LOW);
  //Read echo time 
  duration=pulseIn(echo,HIGH);
  //Calculate distance in cm
  distance=duration*0.034/2;
  //Display result
  Serial.println("distance=");
  Serial.print(distance);
  Serial.println("cm");
  if(distance<=300)
  {
  digitalWrite(LED,HIGH);
  }
  else
  {
  digitalWrite(LED,LOW);
  }
  delay(500);
}