Different pieces of code I modified/created for the OnionOmega.
The Python code does not reliably work on the Onion Omega2. This is a modified version of the C code provided by NCD.IO. Follow these instructions to support building the code on your Omega2.
On my Omega2+ the compile took only a few seconds. Compile with:
gcc AD7999_4channel.c -o AD7999
The most basic version to just read the raw ADC value. For my own needs I don't need absolute ppm values. I've tested this in clear air and introduced small amounts of propane and I get reproducable results. A quick test for your own sensor is to point a propane torch (for plumbing use) at it an open it. This will spike the reading to the highest you should ever see.
You can probably pull the required math from this. But the updated code for the Omega did not provide meaningfull results
Version modified to work on the Onion Omega. You will need to load some extra kernel modules to make this work properly. I've tested this with the 70A, 3 channel model.