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#include <HCSR04.h>
#define LED_PIN 4

HCSR04 hc(5, 6); //initialisation class HCSR04 (trig pin , echo pin)
const int buttonPin = 2;
const int buzzer = 3;

void setup()
{
    pinMode(buttonPin, INPUT);
    Serial.begin(9600);
    const int buttonPin = 2;
    pinMode(LED_PIN, OUTPUT);
    pinMode(buzzer, OUTPUT);
}

void loop()
{
    delay(60);                 //Use over 60ms measurement cycle, in order to prevent trigger signal to the echo signal.
// variables will change:
int buttonState = 0;  // variable for reading the pushbutton status
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);
  Serial.println(hc.dist()); // return curent distance in serial
 // check if the pushbutton is pressed. If it is, the buttonState is HIGH:
  if (buttonState == HIGH) {
    // turn LED on:
    digitalWrite(buttonPin, HIGH);
    Serial.println(buttonState);
    digitalWrite(LED_PIN, HIGH);
    tone(buzzer, 1000);
  } 
  else {
    // turn LED off:
    digitalWrite(buttonPin, LOW);
    Serial.println(buttonState);
    digitalWrite(LED_PIN, LOW);
    noTone(buzzer);
  }
}