Updated basic examples

examples/MQ-7/MQ-7.ino

@@ -26,6 +26,7 @@
 #define pin A0 //Analog input 0 of your arduino
 #define type "MQ-7" //MQ7
 #define ADC_Bit_Resolution 10 // For arduino UNO/MEGA/NANO
+#define RatioMQ7CleanAir 27.5 //RS / R0 = 27.5 ppm 
 //#define calibration_button 13 //Pin to calibrate your sensor
 
 //Declare Sensor
@@ -49,8 +50,28 @@ void setup() {
   Alcohol | 40000000000000000 | -12.35
   */
   
-  // Calibration setup
-  MQ7.setR0(4);
+  
+  /*****************************  MQ CAlibration ********************************************/ 
+  // Explanation: 
+  // In this routine the sensor will measure the resistance of the sensor supposing before was pre-heated
+  // and now is on clean air (Calibration conditions), and it will setup R0 value.
+  // We recomend execute this routine only on setup or on the laboratory and save on the eeprom of your arduino
+  // This routine not need to execute to every restart, you can load your R0 if you know the value
+  // Acknowledgements: https://jayconsystems.com/blog/understanding-a-gas-sensor
+  Serial.print("Calibrating please wait.");
+  int calcR0 = 0;
+  for(int i = 0; i<=10; i ++)
+  {
+    MQ7.update(); // Update data, the arduino will be read the voltage on the analog pin
+    calcR0 += MQ7.calibrate(RatioMQ7CleanAir);
+    Serial.print(".");
+  }
+  MQ7.setR0(calcR0/10);
+  Serial.println("  done!.");
+  
+  if(isinf(calcR0)) {Serial.println("Warning: Conection issue founded, R0 is infite (Open circuit detected) please check your wiring and supply"); while(1);}
+  if(calcR0 == 0){Serial.println("Warning: Conection issue founded, R0 is zero (Analog pin with short circuit to ground) please check your wiring and supply"); while(1);}
+  /*****************************  MQ CAlibration ********************************************/ 
 
   /* 
     //If the RL value is different from 10K please assign your RL value with the following method: