Added smoke example

examples/smokeDetector/smokeDetector.ino

@@ -0,0 +1,51 @@
+/*
+  MQUnifiedsensor Library - smokeDetector
+  
+  Demonstrates the use a MQ2 sensor.
+  Library originally added 01 may 2019
+  by Miguel A Califa, Yersson Carrillo, Ghiordy Contreras, Mario Rodriguez
+ 
+  Added example
+  modified 23 May 2019
+  by Miguel Califa 
+
+ This example code is in the public domain.
+
+*/
+
+//Include the library
+#include <MQUnifiedsensor.h>
+
+//Definitions
+#define pin A0 //Analog input 0 of your arduino
+#define type 4 //MQ4
+
+//Declare Sensor
+MQUnifiedsensor MQ4(pin, type);
+
+void setup() {
+  //Init serial port
+  Serial.begin(115200);
+  /*****************************  MQInicializar****************************************
+  Input:   
+  Output:  
+  Remarks: This function configure the pinMode
+  ************************************************************************************/ 
+  //init the sensor
+  MQ4.inicializar(); 
+}
+
+  void loop() {
+  /*****************************  MQReadSensor  ****************************************
+  Input:   Gas - Serial print flag
+  Output:  Value in PPM
+  Remarks: This function use readPPM to read the value in PPM the gas in the air.
+  ************************************************************************************/ 
+  //Read the sensor and print in serial port
+  //Lecture will be saved in lecture variable
+  int lecture =  MQ4.readSensor("smoke"); // Return smoke concentration
+  Serial.print("MQ4 smoke ppm lecture: ");
+  Serial.print(lecture);
+  Serial.println(" ppm");
+  delay(400);
+}