const int trigpin=13;
const int echopin=12;
int Led=2;
int buzzer =4;
long duration;
int distance;
void setup()
{
  pinMode(trigpin,OUTPUT);
  pinMode(echopin,INPUT);
  pinMode(Led,OUTPUT);
  pinMode(buzzer,OUTPUT);
  Serial.begin(9600);
}
void loop()
{
  digitalWrite(trigpin,LOW);
  delayMicroseconds(2);
   digitalWrite(trigpin,HIGH);
  delayMicroseconds(10);
  digitalWrite(trigpin,LOW);
  
  duration =pulseIn(echopin,HIGH);
  distance =duration *0.034/2;  //0.034 is sound velocity
  Serial.print("Distance");
  Serial.println(distance);
  if(distance<=100)
  {
    digitalWrite( Led,1);
    
      tone (buzzer,900);
    delay(500);
    tone (buzzer,800);
    delay(500);
   
  }
  else
  {
    digitalWrite( Led,0);
    noTone(buzzer);
  
  }
    
 
}