I just finished building a CO2 air quality monitor using a TTGO T4 board and a MH-Z19B sensor.
I had to build the graphing function from scratch as there are no graphing libraries available for the Arduino/ESP32 ecosystem (that I could find).
The monitor supports the following features:
- CO2 and Temperature monitoring with 100ms updates (faster that the sensor)
- Real time graph with a 3 hour scrolling cycle
- Color codes for CO2 concentration levels
- Auto-scaling graphs
It is pretty much feature complete at the moment. The components are quite expensive but I am happy with the result. For less than $100 it has more functions that more expensive commercial products.
The case, source code and instructions are here: https://github.com/wilyarti/TTGO-T4-Air-Monitor