# 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

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).