I purchased several MQ sensors, originally sourced from DFrobot. The pin connections shown on this RobotShop page (1=output, 2=gnd, 3=Vcc) are wrong, It should read (1=output, 2=Vcc, 3=Gnd). The DFRobot site is also mixed up, , This page https://www.dfrobot.com/wiki/index.php/Analog_Gas_Sensor(MQ2)_(SKU:SEN0127) writes it wrong twice, but the picture is right. This page https://www.dfrobot.com/wiki/index.php/Analog_Gas_Sensor_SKU:SEN0127 removed the incorrect text, and the picture is right. I think pin 2 should be Vcc because their 'Gravity' connector convention has it this way, AND the wire colour on the provided leads is red. Not much to go on.
