const int trigger = 9; 
const int echo = 7; 
const int buzzer = 11; 
void setup() 
{
   pinMode(trigger, OUTPUT); 
   pinMode(echo, INPUT); 
   pinMode(buzzer, OUTPUT);
   Serial.begin(9600); 
}
void loop() 
{
  digitalWrite(trigger,LOW); 
  delayMicroseconds(5); 
  digitalWrite(trigger, HIGH); 
  delayMicroseconds(13); 
  digitalWrite(trigger, LOW); 
  long duration = pulseIn(echo,HIGH);
  long distance = (duration * 0.0343) /2;  
  Serial.print("Sensor distance :");  
  Serial.println(distance);  
  if (distance < 75)  
  tone(buzzer , 100);  
  else 
   noTone(buzzer); 
  delay(500);   
}