Build a "Go Away!" Robot - Easy Starter Project for Kids

#define trigPin 13
#define echoPin 12
#define buzzer 9 //buzzer to arduino pin 9
#define led 11



void setup()
{ Serial.begin (9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
  pinMode(buzzer, OUTPUT); // Set buzzer - pin 9 as an output
  pinMode(led, OUTPUT);
}

void loop()
{ long duration, distance;
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);

duration = pulseIn(echoPin, HIGH);
distance = (duration/2) / 29.1;

 if (distance < 100)

{ tone(buzzer, 98); // Send 1KHz sound signal...
digitalWrite(led,HIGH);
}

else {
noTone(buzzer);
digitalWrite(led,LOW);
}

Serial.print(distance);
Serial.println(" cm");
delay(500);
}