Computes AQI (air quality index) using a Honeywell HPMA115-004 and and STM32.
I'm learning how to STM32. Much of this is code-gen from the STM32CubeIDE.
If you're looking, there's a usable Arduino library for this sensor at PMSensor-HPMA115. (Or just search for it under AQI or HPM etc. in the Arduino Library Manager.)