void checkForUpdates() {
  String mac = getMAC();
  String fwURL = String( fwUrlBase );
  fwURL.concat( mac );
  String fwVersionURL = fwURL;
  fwVersionURL.concat( ".version" );

  Serial.println( "Checking for firmware updates." );
  Serial.print( "MAC address: " );
  Serial.println( mac );
  Serial.print( "Firmware version URL: " );
  Serial.println( fwVersionURL );

  HTTPClient httpClient;
  httpClient.begin( fwVersionURL );
  int httpCode = httpClient.GET();
  if( httpCode == 200 ) {
    String newFWVersion = httpClient.getString();

    Serial.print( "Current firmware version: " );
    Serial.println( FW_VERSION );
    Serial.print( "Available firmware version: " );
    Serial.println( newFWVersion );

    int newVersion = newFWVersion.toInt();

    if( newVersion > FW_VERSION ) {
      Serial.println( "Preparing to update" );

      String fwImageURL = fwURL;
      fwImageURL.concat( ".bin" );
      t_httpUpdate_return ret = ESPhttpUpdate.update( fwImageURL );

      switch(ret) {
        case HTTP_UPDATE_FAILED:
          Serial.printf("HTTP_UPDATE_FAILD Error (%d): %s", ESPhttpUpdate.getLastError(), ESPhttpUpdate.getLastErrorString().c_str());
          break;

        case HTTP_UPDATE_NO_UPDATES:
          Serial.println("HTTP_UPDATE_NO_UPDATES");
          break;
      }
    }
    else {
      Serial.println( "Already on latest version" );
    }
  }
  else {
    Serial.print( "Firmware version check failed, got HTTP response code " );
    Serial.println( httpCode );
  }
  httpClient.end();
}

String getMAC()
{
  uint8_t mac[6];
  char result[14];

  snprintf( result, sizeof( result ), "%02x%02x%02x%02x%02x%02x", mac[ 0 ], mac[ 1 ], mac[ 2 ], mac[ 3 ], mac[ 4 ], mac[ 5 ] );

  mqttclient.publish(mqtt_topics_mac, result);
  //Serial.println("MAC-Adresse: "+String( result )+" cm gesendet");


  char b[25];
  String str;
  str=String(FW_VERSION);
  str.toCharArray(b,25);
  mqttclient.publish(mqtt_topics_version, b);
  Serial.println("Version: "+str+" gesendet");

  return String( result );
}