LP_TIMER(500, HandleHeater);
void HandleHeater() {
  static int currentPart = 0;
  static bool states[PARTS];

  if (inSelectionMode) {
    digitalWrite(ssrPin, LOW);
    return;
  }

  int current = Output/100 * PARTS;

  int last = 0;
  for (int i = 1; i < PARTS; i++) {
    last += states[i] ? 1 : 0;
    if (i) {
      states[i-1] = states[i];
    }
  }
  bool next = current >= last ? true : false;
  if (Output < 1) next = false;
  states[PARTS-1] = next;

  oled.setCursor(128-6*PARTS, 7);
  sprintf(timeBuffer, "%3d", (int)(Output));
  char symbol;
  for (int i = 0; i < PARTS; i++) {
    int index = i - (PARTS - 3);
    symbol = index < 0 ? ' ' : timeBuffer[index];
    oled.invertText(states[i]);
    oled.print(symbol);
    oled.invertText(false);
  }

  if (temperatureSensorError) {
    next = 0;
  }

  digitalWrite(ssrPin, next);
  currentPart++;
  if (currentPart >= PARTS) {
    currentPart = 0;
  }

#ifdef PlotValues
  Serial.print(Setpoint);
  Serial.print(",");
  Serial.print(Input);
  Serial.print(",");
  Serial.print(Output);
  Serial.println(",0,100");
#endif

}