gsuberland, 
if anyone's got some spare time, I'd very much appreciate some technical review of the mk2 CO2/AQI sensor board design for EMF Camp.
full schematics, top/bottom copper, renders, and BoM are in the PDF: https://poly.nomial.co.uk/junk/CO2SensorBoardMk2_20240426.pdf
relevant info:
- ESP8266 devboard plugs in underneath, board is either powered by USB Micro on devboard or USB-C on mainboard
- fab & assembly by JLC
- 4L board, inner layers are solid ground planes
- 4P header is for SSD1306 OLED