diff --git a/platformio.ini b/platformio.ini
index c87cdc1..5442b89 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -16,8 +16,8 @@
 #data_dir=data_sensoresp1
 #data_dir=data_sensoresp2
 #data_dir=data_sensoresp3
-#data_dir=data_sensoresp4
-data_dir=data_sensoresp5
+data_dir=data_sensoresp4
+#data_dir=data_sensoresp5
 
 
 #Outdoor
diff --git a/src/main.cpp b/src/main.cpp
index 21ce707..0f542c1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -15,6 +15,7 @@
 #define FW_NAME "sensoresp"  //gets printed on topic/$fw/name
 #define FW_VERSION "1.0.0"  //gets printed on topic/$fw/version
 
+#define STATUSNODE
 
 struct sensordata
 {
@@ -27,6 +28,7 @@ struct sensordata
 };
 
 
+
 #ifdef SENSOR_DHT22
   // Digital pin connected to the DHT sensor.  // dht pins: 1=power, 2=data, 3=NC, 4=GND. 10k from data to power needed 
   #include <Adafruit_Sensor.h> //required for dht library
@@ -110,7 +112,7 @@ struct sensordata
   /*
   * MHZ19 Library: https://platformio.org/lib/show/1620/SevSegSPI
   * Software Serial Library: https://platformio.org/lib/show/168/EspSoftwareSerial
-  * SDS018 example: https://github.com/crystaldust/sds018/blob/master/sds018.ino
+
   */
   // SW Serial
   //SW Serial RX: to mhz19 tx (green cable)
@@ -142,12 +144,18 @@ struct sensordata
   SoftwareSerial mhz19_swSerial;
   #define BAUD_RATE_MHZ19 9600
 
+  #define MHZ19CALIBRATIONTOPIC
+
   #include <MHZ19.h>
   MHZ19 mhz19;
   bool mhz19_ready=false;
   int value_co2=-1; //[ppm]
 
   int mhz19_readValue_reimplemented(Stream *_streamRef, MHZ19 *_mhz19Ref); //declare function
+
+  #ifdef MHZ19CALIBRATIONTOPIC
+  bool mhz19calibrationHandler(const HomieRange& range, const String& value);
+  #endif
 #endif
 
 
@@ -155,6 +163,8 @@ struct sensordata
   struct sensordata dataSDS018_pm25;
   struct sensordata dataSDS018_pm10;
 
+  // SDS018 example: https://github.com/crystaldust/sds018/blob/master/sds018.ino
+
   //SDS18 dust sensor for 2.5µm and 10µm
   //Needs 5V
 
@@ -252,6 +262,7 @@ void setup() {
 
   delay(1000); //wait for sensors to get powered
 
+
   #ifdef SENSOR_DHT22
     Serial.println("initializing dht");
     dht.begin();
@@ -358,8 +369,11 @@ void setup() {
     if (mhz19abctries>0) {
       Serial.println("mhz19 abc disabled successfully");
     }
+
   #endif
 
+
+
   #ifdef SENSOR_SDS018
     Serial.println("initializing sds018");
     sds018_swSerial.begin(BAUD_RATE_SDS018, SWSERIAL_8N1, SDS018_SERIAL_RX, SDS018_SERIAL_TX, false, 256);
@@ -414,12 +428,19 @@ void setup() {
     #endif
   #endif
 
+
+  // ##### Advertise topics below here #####
   
   //Homie_setFirmware(FW_NAME, FW_VERSION);
   //Homie_setBrand(FW_NAME);
   Homie_setFirmware(FW_NAME, FW_VERSION);
   Homie.setLoopFunction(loopHandler);
 
+  #ifdef STATUSNODE
+    //to return some stuff about status, errors etc.
+    Serial.println("Using status node");
+    sensorNode.advertise("status");
+  #endif
 
   #ifdef SENSOR_DHT22
   
@@ -466,6 +487,9 @@ void setup() {
 
   #ifdef SENSOR_MHZ19
     sensorNode.advertise("co2");
+    #ifdef MHZ19CALIBRATIONTOPIC
+      sensorNode.advertise("mhz19calibration").settable(mhz19calibrationHandler);
+    #endif
   #endif
 
   #ifdef SENSOR_SDS018
@@ -893,6 +917,9 @@ void loop_TCS34725_lux()
       lastread_tcs34725=millis();
       if (tcs.isSaturated){
         Serial.println("Warning: tcs34725 is saturated");
+        #ifdef STATUSNODE
+        sensorNode.setProperty("status").send("TCS34725 is saturated");
+        #endif
       }
     }
     //value_tcs_lux = tcs.calculateLux(value_tcs_r, value_tcs_g, value_tcs_b);
@@ -1308,6 +1335,32 @@ void ICACHE_RAM_ATTR interrupt_raingauge()
 #endif
 
 
+/* #################################
+*  ########### topic handler #######
+*/
+
+#ifdef MHZ19CALIBRATIONTOPIC
+  bool mhz19calibrationHandler(const HomieRange& range, const String& value) {
+  if (range.isRange) {
+    return false; //if range is given but index is not in allowed range
+  }
+  Homie.getLogger() << "mhz19 calibration " << ": " << value << endl;
+  
+  if (value=="zero") {
+    mhz19.calibrateZero();
+    Homie.getLogger() << "mhz19 calibration " << ": " << value << endl;
+    #ifdef STATUSNODE
+    sensorNode.setProperty("status").send("MHZ19 Zero Calibration triggered");
+    #endif
+  } else {
+    Homie.getLogger() << "Value outside range" << endl;
+    return false;  
+  }
+  
+  return true;
+}
+#endif
+
 
 /*##################################
 * ######## HELPER FUNCTIONS ########