diff --git a/.gitignore b/.gitignore
index d398f9d..75ec3f0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1 @@
-
-.vscode/arduino.json
-.vscode/c_cpp_properties.json
+.vscode/*
\ No newline at end of file
diff --git a/MHZ.cpp b/MHZ.cpp
index 4510232..0da32da 100644
--- a/MHZ.cpp
+++ b/MHZ.cpp
@@ -8,16 +8,24 @@
 const int MHZ14A = 14;
 const int MHZ19B = 19;
 
-const int MHZ14A_RESPONSE_TIME = 60;
-const int MHZ19B_RESPONSE_TIME = 120;
+const int MHZ14A_PREHEATING_TIME = 3 * 60 * 1000;
+const int MHZ19B_PREHEATING_TIME = 3 * 60 * 1000;
+
+const int MHZ14A_RESPONSE_TIME = 60 * 1000;
+const int MHZ19B_RESPONSE_TIME = 120 * 1000;
 
 const int STATUS_NO_RESPONSE = -2;
 const int STATUS_CHECKSUM_MISMATCH = -3;
 const int STATUS_INCOMPLETE = -4;
 const int STATUS_NOT_READY = -5;
+const int STATUS_PWM_NOT_CONFIGURED = -6;
+const int STATUS_SERIAL_NOT_CONFIGURED = -7;
 
 unsigned long lastRequest = 0;
 
+bool SerialConfigured = true;
+bool PwmConfigured = true;
+
 MHZ::MHZ(uint8_t rxpin, uint8_t txpin, uint8_t pwmpin, uint8_t type) {
   SoftwareSerial * ss = new SoftwareSerial(rxpin, txpin);
   _pwmpin = pwmpin;
@@ -27,10 +35,34 @@ MHZ::MHZ(uint8_t rxpin, uint8_t txpin, uint8_t pwmpin, uint8_t type) {
   _serial = ss;
 }
 
+MHZ::MHZ(uint8_t rxpin, uint8_t txpin, uint8_t type) {
+  SoftwareSerial * ss = new SoftwareSerial(rxpin, txpin);
+  _type = type;
+
+  ss->begin(9600);
+  _serial = ss;
+
+  PwmConfigured = false;
+}
+
+MHZ::MHZ(uint8_t pwmpin, uint8_t type) {
+  _pwmpin = pwmpin;
+  _type = type;
+
+  SerialConfigured = false;
+}
+
 MHZ::MHZ(Stream * serial, uint8_t pwmpin, uint8_t type) {
-    _serial = serial;
-    _pwmpin = pwmpin;
-    _type = type;
+  _serial = serial;
+  _pwmpin = pwmpin;
+  _type = type;
+}
+
+MHZ::MHZ(Stream * serial, uint8_t type) {
+  _serial = serial;
+  _type = type;
+
+  PwmConfigured = false;
 }
 
 /**
@@ -47,9 +79,9 @@ void MHZ::setDebug(boolean enable) {
 
 boolean MHZ::isPreHeating() {
   if (_type == MHZ14A) {
-    return millis() < (3 * 60 * 1000);
+    return millis() < (MHZ14A_PREHEATING_TIME);
   } else if (_type == MHZ19B) {
-    return millis() < (3 * 60 * 1000);
+    return millis() < (MHZ19B_PREHEATING_TIME);
   } else {
     Serial.println(F("MHZ::isPreHeating() => UNKNOWN SENSOR"));
     return false;
@@ -71,6 +103,10 @@ boolean MHZ::isReady() {
 }
 
 int MHZ::readCO2UART() {
+  if (!SerialConfigured) {
+    if (debug) Serial.println(F("-- serial is not configured"));
+    return STATUS_SERIAL_NOT_CONFIGURED;
+  }
   if (!isReady()) return STATUS_NOT_READY;
   if (debug) Serial.println(F("-- read CO2 uart ---"));
   byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
@@ -170,12 +206,20 @@ int MHZ::readCO2UART() {
   return ppm_uart;
 }
 
-uint8_t MHZ::getLastTemperature() {
+int MHZ::getLastTemperature() {
+  if (!SerialConfigured) {
+    if (debug) Serial.println(F("-- serial is not configured"));
+    return STATUS_SERIAL_NOT_CONFIGURED;
+  }
   if (isPreHeating()) return STATUS_NOT_READY;
   return temperature;
 }
 
 byte MHZ::getCheckSum(byte* packet) {
+  if (!SerialConfigured) {
+    if (debug) Serial.println(F("-- serial is not configured"));
+    return STATUS_SERIAL_NOT_CONFIGURED;
+  }
   if (debug) Serial.println(F("  getCheckSum()"));
   byte i;
   unsigned char checksum = 0;
@@ -188,7 +232,11 @@ byte MHZ::getCheckSum(byte* packet) {
 }
 
 int MHZ::readCO2PWM() {
-  // if (!isReady()) return STATUS_NOT_READY; not needed?
+  if (!PwmConfigured) {
+    if (debug) Serial.println(F("-- pwm is not configured "));
+    return STATUS_PWM_NOT_CONFIGURED;
+  }
+  //if (!isReady()) return STATUS_NOT_READY; not needed?
   if (debug) Serial.print(F("-- reading CO2 from pwm "));
   unsigned long th, tl, ppm_pwm = 0;
   do {
diff --git a/MHZ.h b/MHZ.h
index 86a052f..cd2c2fb 100644
--- a/MHZ.h
+++ b/MHZ.h
@@ -26,7 +26,10 @@ extern const int STATUS_NOT_READY;
 class MHZ {
  public:
   MHZ(uint8_t rxpin, uint8_t txpin, uint8_t pwmpin, uint8_t type);
+  MHZ(uint8_t rxpin, uint8_t txpin, uint8_t type);
+  MHZ(uint8_t pwmpin, uint8_t type);
   MHZ(Stream * serial, uint8_t pwmpin, uint8_t type);
+  MHZ(Stream * serial, uint8_t type);
 
   void setDebug(boolean enable);
 
@@ -35,7 +38,7 @@ class MHZ {
 
   int readCO2UART();
   int readCO2PWM();
-  uint8_t getLastTemperature();
+  int getLastTemperature();
 
  private:
   uint8_t _pwmpin, _type, temperature;
diff --git a/examples/MH-Z19B/MH-Z19B.ino b/examples/MH-Z19B/MH-Z19B.ino
index 80e2143..65925b1 100644
--- a/examples/MH-Z19B/MH-Z19B.ino
+++ b/examples/MH-Z19B/MH-Z19B.ino
@@ -1,13 +1,11 @@
-
-
 #include <ESP8266WiFi.h>
 #include <SoftwareSerial.h>
-#include "MHZ.h"
-
-// pin for uart reading
-#define CO2_IN 10
+#include <MHZ.h>
 
 // pin for pwm reading
+#define CO2_IN 10
+
+// pin for uart reading
 #define MH_Z19_RX D4  // D7
 #define MH_Z19_TX D0  // D6
 
@@ -38,9 +36,12 @@ void loop() {
   Serial.println(" s");
 
   int ppm_uart = co2.readCO2UART();
+  Serial.print("PPMuart: ");
+
   if (ppm_uart > 0) {
-    Serial.print("PPMuart: ");
     Serial.print(ppm_uart);
+  } else {
+    Serial.print("n/a");
   }
 
   int ppm_pwm = co2.readCO2PWM();
@@ -48,9 +49,12 @@ void loop() {
   Serial.print(ppm_pwm);
 
   int temperature = co2.getLastTemperature();
+  Serial.print(", Temperature: ");
+
   if (temperature > 0) {
-    Serial.print(", Temperature: ");
     Serial.println(temperature);
+  } else {
+    Serial.println("n/a");
   }
 
   Serial.println("\n------------------------------");
diff --git a/library.properties b/library.properties
index b490aac..6c9328e 100644
--- a/library.properties
+++ b/library.properties
@@ -1,5 +1,5 @@
 name=MH-Z CO2 Sensors
-version=1.1.0
+version=1.2.0
 author=Tobias Schürg
 maintainer=Tobias Schürg
 sentence=Ready to use imeplementation for CO2 sensors of the MHZ series (Intelligent Infrared CO2 Module)