Making Sense of data from MQ2 Combustible Gas Sensor?

Hi Guys,

The literature that came with this kit might have well as been non-existant. I have a sensor I've wired to my arduino uno, and it looks like it's working. For instance, it typically reads around 150-200 with just the ambient air, but when I focus my butane lighter on it, it'll jump up into the 600-700 range - so I guess it's working.

I assume the key figure I should look at is the 'sensing resistance' (from 2K ohms - 20K ohms)? I'm trying to figure out what arduino is telling me when it's giving me the reading of 150-200 with ambient air, or 600-700 when I push butane to the sensor?

Here's the technical data I found on a sensor that looks pretty similar:

I'm trying to have the arduino tell me the percentage of combustibles in the air, and if I can fine tune it for HHO gas, even better.

Thanks for any tips :slight_smile:

The problem is that the resistance called R0 is something you are supposed to measure with the sensor in a 1000 PPM concentration of H2. Most people don't have that test standard readily available.

Look at the chart in the datasheet to see what RS/R0 you should be getting in clean air. Looks to be about 9.6 to me. From your voltage (reading * 5.0 / 1024.0) and your RL, calculate the resistance you are measuring. Then divide that by 9.6 to calculate R0. Then you can use the chart to get estimates of concentration from Rs/R0.

In the Playground is a page for MQ gas sensors : http://playground.arduino.cc/Main/MQGasSensors
After the preheat time, you try to find a resistor that seems fine.

After the preheat, and when the 5V is accurate, and when the sensor has warmed up for a few minutes, the values are stable. Suppose the normal values are 115...120, you can raise an alarm at 150 (just a whild guess, but you get the idea).