MQ2 Gas Sensor Pinout, Features, Equivalents & Datasheet Jan 04, 2018Operating Voltage is +5V. Can be used to Measure or detect LPG, Alcohol, Propane, Hydrogen, CO and even methane. Analog output voltage: 0V to 5V. Digital Output Voltage: 0V or 5V (TTL Logic) Preheat duration 20 seconds. Can be used as a Digital or analog sensor. MQ135 Alcohol Sensor Circuit and Its Working - elprocus It is a simple drive circuit; This is about the MQ135 alcohol sensor circuit diagram and the working operation and its applications. We hope that the given information in the article is helpful to you in gaining some good knowledge and understanding the project.