My testing with the SGP30 sensor proved fruitless, as various sensors
would mis-report (under- and over-) levels and generally not be
consistent with each other or reality. These sensors are simply too
flaky with zero consistency.
Instead, switch to the SGP41, which so far seems more robust and is used
in other tools like the AirGradient One. We leverage their calculations
for VOC Index -> VOC levels, as well as a generalized isobutylene-based
eCO2 calculation.
This library proved to be just as useless for reliable IAQ as the
original BSEC library (swinging wildly based on nothing at all), so
revert back to tag 1.2 and ESP-IDF.
Implements an AQ calculation from [1], which should hopefully provide a
more stable, sensible value for the air quality.
This also adds a configurable gas ceiling level, needed for full
calibration and explained in the README.
[1] https://github.com/thstielow/raspi-bme680-iaq
The human text ratings are still a work-in-progress.
