const int ledPin = 8;
const int buzzerPin = 7;
const int trigPin = 9;
const int echoPin = 10;

long duration;
int distance;
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);
    
    if(distance<10){
      tone(buzzerPin,1000);
    }else{
      tone(buzzerPin,500);
    };
    
  }else{
    digitalWrite(ledPin, LOW);
    noTone(buzzerPin);
  }
  
  Serial.println("Object Distance: ");
  Serial.print(distance);
  Serial.print("cm");

}