Android usb serial for direct read

[dwhitemv (Doug White)]

The serial output format is described in this post, though it doesn’t explain the gas output:

Understanding PurpleAir Serial Output

When using the PurpleAir Utility or a Classic-SD sensor modified to record SD data every second data is not in CSV format. Instead, it is in a custom format described below, which may require additional processing to use. 1-second Reports Every second, one of the laser counters will report. Five reports will be recorded from channel A, then five reports from channel B. This process repeats until the next 2-minute report. This 2-minute report is the averaged data that is uploaded to our API as “…

You can get the field descriptions from the chip’s datasheet:

• p: Pressure in millibars/hPa
• iaq: Index for Air Quality (mobile sensor), like EPA AQI
• T: Temperature
• H: Humidity
• sIaq: Static Index for Air Quality (“static” meaning “stationary” here), like EPA AQI; is not subject to the auto-trim algorithm like iaq is
• gasR: Gas resistance value (raw reading of the sensing device, may or may not be temperature- and humidity-compensated depending on which field they’re reading)

There may be more fields depending on which chip your sensor is equipped with. I linked the datasheet for the BME688, but I believe older sensors may have the predecessor chip, the BME680.