Eiechip 9PCS/Lot Gas Detection Sensor Module MQ-2 MQ-3 MQ-4 MQ-5 MQ-6 MQ-7 MQ-8 MQ-9 MQ-135 Sensor Module Gas Sensor Starter Kit

Most of the sensors are triggered by more than one substance, so it's virtually impossible to know WHAT is triggering the sensor. Many of the sensors are triggered by similar gases. None of the sensors are calibrated, so you cannot measure concentrations of any specific gas. Each sensor provides an Analog outpout that is somewhat proportional to the level of the gases the sensor is designed to detect. But you cannot know for sure exactly which gas is triggering the sensor. The analog outputs do not seem to be linear either. There is also a digital output pin that can be set (using a potentiometer) to set the digital pin high when a sensor level is exceeded. When the digital pin goes high, a Green LED on the sensor board lights up. Technically, you can use the sensors just hooking power to them, and relying on the Green LED to tell you when the preset level has been exceeded. The digital pin could also be used to trigger an alarm. If you want to read the Analog output, you could connect to something like an Arduino or Raspberry Pi and create a program, or you could hook an analog meter to the pin. There is a lot of versatility hear.... Don't rely on these to monitor hazardous environements as these are intended for hobby use.Update: Hooked up several of the sensors to monitor the indoor air quality of my house. Ran all sensors for 48 hours to get them burned in propertly. Started to test each sensor and monitor its analog output using various substances. Tracked the Min, Max, and Current measurements. Used the following samples to test how each sensor reacted.Paper towel wet with 91% isopropyl alcoholButane grill lighterBalloon filled with Natural Gas from service port on my gas meterResults.Waved the paper towel in front of each sensor for ~ 5 secondsEVERY sensor reacted to the alcohol, even sensors that are not particularly designed to respond to alcoholIt took about half an hour for readings to drop back to ambient.... then tried Butane.Pressed button to release Butane gas from lighter for 2 seconds with nozzel up against sensor.Again, EVERY sensor reacted to the ButaneAnother half hour, then tried Natural Gas (Methane).Slightly opened end of balloon for 1 second right in front of each sensorAgain, EVERY sensor reacted to the Natural Gas.Starting to see a pattern here. It is virtually impossible to use any of the sensors to know what gas is being detected, so now I am starting to question their practicality.None of the sensors analog outputs start anywhere near ZERO, so you need to operate them in clear air for a while to see what the "no detection" value is, and use that as an offset.I couldn't get any of the sensors to generated an analog output greater than 921. I am not sure if that's because I setup my Arduino to use AREF = 5volts and maybe the sensor outputs are scaled to use a lower voltage. In general, the sensors Analog reference values are around 400, only the MQ2 sensor started at ~200. All the sensor's Analog outputs peaked ~800 +- 100. Looks like each sensor will change a maximum of 400 from detecting "nothing", to what I figured is "saturation".

These are the standard sensor units, they work. Takes a bit of time to get them to stabilize and provide reliable readings - usually 10 minutes or so. Use them to measure particulates in a 3D Printing enclosure and so far they work very well. These sensors are all 5V and work well.Only challenge I had was some of them were not broken out yet (the frame PCB was still attached), so use a pliers to break them off. Don't use your hands, they're sharp!

Not sure how these are supposed to work. The internet at large only knows about the raw sensors, and has no idea what to do with the modules or how they work.1 star review to get some support, these are sitting on my shelf until I figure out how they work.

Who would have thought you could buy one of these at this price? Nine? are you kidding? Super deal.

Packaged nicely in little sealed antistatic pods. Came dressed in official Arduino blue soldermask.

This is a nice selection of gas sensors for a wide variety of atmospheric pollutants. It is very easily interfaced to an Arduino-like microcontroller and gives repeatable but uncallibrated results.

Great sensors for Arduino use. Lots of information online about use with the Arduino. Seller also has available circuit diagram for circuit board which the sensors are mounted on.

A great variety of gas sensors for different projects! I used the propane sensor for a camper van arduino console. Working good so far!