https://youtu.be/hSYCt7LrYxQ Video instructivo /*MQ2 sensor with Arduino.  * https://srituhobby.com  */    # include  <LiquidCrystal_I2C.h>  LiquidCrystal_I2C lcd ( 0x27 ,  16 ,  2 ) ;   # define  LED 2  # define  Buzzer 3  # define  Sensor A1   void  setup ( )  {    Serial . begin ( 9200 ) ;    lcd . init ( ) ;    lcd . backlight ( ) ;    pinMode ( LED ,  OUTPUT ) ;    pinMode ( Buzzer ,  OUTPUT ) ;  }   void  loop ( )  {    int  value =  analogRead ( Sensor ) ;    lcd . setCursor ( 0 ,  0 ) ;    lcd . print ( "Value :" ) ;    lcd . print ( value ) ;    lcd . print ( "  " ) ;     if  ( value >  400 )  {      digitalWrite ( LED ,  HIGH ) ;      digitalWrite ( Buzzer ,  HIGH ) ;      lcd . setCursor ( 0 ,  1 ) ;      lcd . print ( "GAS Detected!" ) ;    }  else  {      digitalWrite ( LED ,  LOW ) ;      digitalWrite ( Buzzer ,  LOW ) ;      lcd . setCursor ( 0 ,  1 ) ;      lcd . print ( "             " ) ;    }  }