void irSensor() {
  static unsigned long last_interrupt_time = 0;
  unsigned long interrupt_time = millis();
  // If interrupts come faster than 200ms, assume it's a bounce and ignore
  if (interrupt_time - last_interrupt_time > 200) 
  {
    tripSensor();
  }
  last_interrupt_time = interrupt_time;
}

void tripSensor() {
  unsigned long time = millis();
  if (mode == MODE_RESTING) {
    if (time < restExpires) return; // Ignore signals while resting
    mode = MODE_SPINUP;
    lastTime = 0;
  }

  if (mode == MODE_COUNTING && recordedTimes < maxTimes) {
    times[recordedTimes++] = time;
    if (recordedTimes == maxTimes) {
      mode = MODE_RESTING;
      restExpires = time + 30000;
    }
  }

  if (mode == MODE_SPINUP && lastTime == 0) {
    lastTime = time;
    showShape(4);
    return;
  }
  if (mode == MODE_SPINUP && lastTime != 0) {
    double duration = time - lastTime;
    double mph = durationToMph(duration);
    lastTime = time;
    showNumber(mph);
    return;
  }
  if (mode == MODE_COUNTING && recordedTimes == 1) {
    showShape(4);
    showNumberLAP(0);
    return;
  }
  if (mode == MODE_COUNTING && recordedTimes > 1) {
    double duration = times[recordedTimes - 1] - times[recordedTimes - 2];
    double mph = durationToMph(duration);
    showNumber(mph);
    showNumberLAP(recordedTimes - 1);
    return;
  }
  if (mode == MODE_RESTING) {
    double duration = averageTime();
    double mph = durationToMph(duration);
    showNumber(mph);
    showNumberLAP(recordedTimes - 1);
    return;
  }
}

double averageTime() {
  if (recordedTimes > 0) {
    double sum = 0;
    for (int i = 1; i < recordedTimes; i++) {
      sum = sum + (double)(times[i] - times[i - 1]);
    }
    double average = sum / (double)recordedTimes;
    return average;
  } else {
    return 0;
  }
}

double durationToMph(double duration) {
  seconds = (duration/1000);
  hours = (duration/3600000);
  mph = (distance/hours);
  return mph;
}