int tripin= 7;
int echopin= 8;
int led = 9; 
int duration ; 
int distance ;

void setup()
{
pinMode(tripin, OUTPUT);
pinMode(led, OUTPUT);
pinMode(echopin, INPUT);
Serial.begin(9600);
}
void loop()
{
digitalWrite(tripin, LOW);
delay(2);
digitalWrite(tripin, HIGH);
delay(10);
digitalWrite(tripin, LOW);
duration=pulseIn(echopin,HIGH);
distance=duration*0.034/2;
Serial.println("distance:");
Serial.println(distance);
Serial.println("CM");

if(distance<30)
{
digitalWrite(led, HIGH);
Serial.println("distance is less than 30");
}
else 
{
digitalWrite(led, LOW);
Serial.println("distance is greater than 30");
}

}