Hello Epierre, I'm working in a proyect and i'm using MQ131 sensor, but I have a problem with the Arduino Code. I've seen the page (https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino) but I have a problem because my sensor readings are 0. if you would be so kind, could you send me only the code of sensor MQ131 ??. Thank you very much!!