int trigPin = 3;
int echoPin = 4;
float duration;
float distance;

void setup() {
  Serial.begin (9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(9, OUTPUT);
  pinMode(10, INPUT);

}
void(* resetFunc) (void) = 0; //declare reset function at address 0


void loop() {

  // long duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(100);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  //Serial.print(duration);
  distance = (duration / 2) / 29.1; //microsecond
  //---------------------------------------------------------------- this part above is for the distance sensor HC-SR04
  if (distance >= 400 || distance <= 2) {  //range of the sensor
    Serial.println("Out of range");
  }
  else {
    Serial.print(distance);
    Serial.println(" cm ");

  }

  digitalWrite(9, LOW);

  while (distance > 2 && distance < 10) {  //if your hand/an object is less than 10cm from the sensor, led will turn on. You can change the range.
    digitalWrite(trigPin, LOW);
    delayMicroseconds(2);
    digitalWrite(trigPin, HIGH);
    delayMicroseconds(100);
    digitalWrite(trigPin, LOW);
    duration = pulseIn(echoPin, HIGH);
    distance = (duration / 2) / 29.1; //microsecond

    digitalWrite(9, HIGH);
    delay(50);// prevent the bouncing
    // delay( millisecconds );

    while (distance > 10) {  //if you move your hand from the sensor, led still have to turn on.
      digitalWrite(trigPin, LOW);
      delayMicroseconds(2);
      digitalWrite(trigPin, HIGH);
      delayMicroseconds(100);
      digitalWrite(trigPin, LOW);
      duration = pulseIn(echoPin, HIGH);
      distance = (duration / 2) / 29.1; //microsecond

      digitalWrite(9, HIGH);
      delay(50);// prevent the bouncing

      while (distance > 2 && distance < 10) {  //the next time that you move your hand/object closer than 10cm from the sensor, led will turn off
        digitalWrite(trigPin, LOW);
        delayMicroseconds(2);
        digitalWrite(trigPin, HIGH);
        delayMicroseconds(100);
        digitalWrite(trigPin, LOW);
        duration = pulseIn(echoPin, HIGH);
        distance = (duration / 2) / 29.1; //microsecond

        digitalWrite(9, LOW);
        delay(50);// prevent the bouncing
        while (distance > 10) {
          digitalWrite(trigPin, LOW);
          delayMicroseconds(2);
          digitalWrite(trigPin, HIGH);
          delayMicroseconds(100);
          digitalWrite(trigPin, LOW);
          duration = pulseIn(echoPin, HIGH);
          distance = (duration / 2) / 29.1; //microsecond
          
          digitalWrite(9, LOW);
          delay(50);// prevent the bouncing
          resetFunc();
        }
      }
    }
  }
}