const uint8_t MIN_PWM = 65;
    const uint8_t MAX_PWM = 255;
    pwm = map(avg, 1, limit, MIN_PWM, MAX_PWM);

const unsigned long SAMPLE_PERIOD = 1000;
unsigned long lastSampleTime = 0;

void loop() {
  unsigned long now = millis();
  if (now - lastSampleTime < SAMPLE_PERIOD) return;
  lastSampleTime = now;

  int adc = analogRead(LDR_PIN);
  adc = ldrIsBottom ? 1023 - adc : adc;
  if (adc > limitAdc) adc = limitAdc;

  sum -= buffer[index];
  buffer[index] = adc;
  sum += adc;
  if (++index >= N) index = 0;

  int avg = sum / N;

  static uint8_t pwm = 0;
  static int lastAdc = 0;

  // OFF → START / RUN
  if (avg > 0) {
    lastAdc = avg;
    lastRiseTime = now;
  }

  if (lastAdc > 0 || avg > 0) {

    const uint8_t START_AVG = 4;

    if (avg == 0) avg = lastAdc;

    // START state
    if (pwm == 0 && avg < START_AVG) {
      pwm = START_AVG * 10;
    }
    // RUN or HOLD
    else {
      pwm = avg * 10;
    }

    // HOLD → OFF
    if (now - lastRiseTime >= HOLD_TIME) {
      lastAdc = 0;
      pwm = 0;
    }

    OCR2B = pwm;
  }
}