Sensing #methane with #Arduino started as an idea for student projects, and since then it developed beyond.
It is an old idea to have a tricorder-like device to measure traces in the atmosphere. We are a bit closer to it with the microcontroller Arduino and tin oxide sensors, at least if we talk about methane, LPG and alcohols.
Recently, I have been testing MQ sensors with Arduino. These cheap sensors (<5 EUR) have been used for safety-alarm systems, so high concentrations alarm trigger is the most common use so far. However, I had an impression that there is a potential in using them for a scientific project, even so, when we talk about ambient concentrations.
To follow that idea, I designed an on-desk system to measure methane, and my goal was to use small volumes of the sample, <5 mL. At the end I come up with something like this:
With the injection of as low as 2 mL, I was surprised to see the distinctive peaks. I tried a different concentration, and it seemed it was working pretty good.
Then the time came to add more elements to the system such as data logging board so that I could store the data for further analysis. This was possible but required some coding to get data saved in the desired format for further processing. The signal processing also needed an automated integration, well, more coding. In the end, I was able to perform the first 'systematic' measurement, and to my surprise, the detection limit was < 1ppm.
LOD < 1PPM
Yes, I measured sub-ambient levels of methane with a 4 EUR sensor, and the reproducibility was good too. The signal increase with concentration linearly (the most desired behaviour) which allowed an easy calibration.
However, there are a lot of other challenges. For instance, selectivity should be tested. These sensors can as well detect alcohols and other alkanes with different efficiency, so the potential interference should be considered. The sensors also respond to the humidity and temperature changes, which means that the system needs stable conditions or well-defined correction method.
In conclusion, this is a low-cost methane system for the lab use, frequent calibration is needed, and the time-resolution depends on the loaded concentration (2 min for ambient levels, 4 min for 10 ppm, more than 10 min for 50 ppm). It will not get portable or give a direct concentration output any time soon (e.g. without the post-processing script), but I had a lot of fun and will try to improve it.