led_bikewheel/led_bikewheel.ino

const int HALL_PIN = 2;
const int ROUND_COUNT = 2;

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(HALL_PIN, INPUT);
}

void loop() {
  float start = micros();
  int count = 0;
  bool change = false;
  while (count < ROUND_COUNT) {
    if (digitalRead(HALL_PIN) == LOW) {
      if(!change) {
        change = true;
        count++;
      }
    } else {
      change = false;
    }
  }

  float end = micros();
  float passed = (end - start);
  Serial.print("Diff: ");
  Serial.print(passed);
  Serial.println("micro seconds");
 
}