const int ledPin = 9;
const int buzzerPin = 10;
const int echoPin = 11;
const int trigPin = 12;

long duration = 0;
int distance = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);  
  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;
 if(distance>20){
  digitalWrite(ledPin, HIGH);
  tone(buzzerPin, 1000);
 }else{
  digitalWrite(ledPin, LOW);
  noTone(buzzerPin);
 }
  Serial.print("Distance: ");
  Serial.println(distance);
  Serial.println("cm");
  delay(1000);

}