Converting raw values from MICS6814 into ppm

Hi @razzor1984, unfortunately this doesn't make too much sense as the sensors pick up a mix of gasses. this is what Pimoroni explains on their website:

https://learn.pimoroni.com/tutorial/sandyj/getting-started-with-enviro-plus

MICS6814 analog gas sensor and ADS1015 analog to digital converter (ADC) The MICS6814 is an analog gas sensor that can detect three different groups of gases that they refer to in the datasheet as reducing, oxidising, and NH3. The major gases/vapours that the sensor detects are: carbon monoxide (reducing), nitrogen dioxide (oxidising), and ammonia (NH3), but it is also sensitive to others, including hydrogen, ethanol, and hydrocarbons.

Each of the three groups of gases is effectively its own sensor within the MICS68141, and the analog voltage readings that the sensor produces are read by an analog to digital converter (ADC) and then converted into resistances by our code. These resistances will range from low hundreds of Ohms to tens of thousands of Ohms, and vary depending on the levels of each group of gases.

Because each group of gases could be a mix of different gases, it's not possible to single out any one gas specifically or to quantify their levels precisely, so the best way to interpret the data is to take readings until they stabilise, set a baseline, and then look for changes relative to that baseline. This gives you a rough idea of whether the air quality is increasing or decreasing.

The reducing and NH3 resistance readings will drop with increasing concentrations of the gases that they detect, and the oxidising sensor will increase with increasing levels of nitrogen dioxide. You can see how the sensor reacts to the different gases in the charts below.

tijmenvandenbrink / enviroplus_exporter

Converting raw values from MICS6814 into ppm #8