I made these ages ago, but they have moved on a little. I may add more "air quality" type stuff in future, but for now they are temperature, humidity and CO₂. I have updated for a colour display.
The new house has coax cabling in place, which is no use to me, so I have redeployed as 12V DC supply so I can install these on existing single gang back boxes.
The main thing is that they are all on GitHub. This includes the code, PCB, and 3D case designs. This includes linux code to log the MQTT to a database. It also can send MQTT for controlling heating and ventilation based on temperature and CO₂ levels, which I am using with tasmota flashed relays (Shelly).
The PCB is now all KiCad, so easy to get printed properly.
The 3D case design has been fun - I made code to generate an SCAD model from the KiCad PCB layout so ensuring all connectors, and spacing for all components is always accurate. That was fun! I have included simple boxes with USB-C socket and also one gang face place boxes, with and without OLED or CO₂ sensor.
So have fun.
P.S. I have updated the repository Documentation to have detailed step by step instructions with pictures for building these.