void loop() {
  /*
  ...
  */
  if (Serial.available()) {
    c = Serial.read();
    serialBuffer += c;
    if (c == '\n') {
      receivedCmd = true;
    }
  }

  if (receivedCmd) {
    receivedCmd = false;
    Serial.print(serialBuffer);
    if (serialBuffer.startsWith(CMD_OPEN_FORTOCHKA)) {
      openFortochka();
    } else if (serialBuffer.startsWith(CMD_CLOSE_FORTOCHKA)) {
      closeFortochka();
    } else if (serialBuffer.startsWith(CMD_GET_HELP)) {
      printHelp();
    }
    serialBuffer = "";
  }
}