This project is about hacking the Voltcraft CO-100 CO2-sensor, such that we can read the exact ppm value as displayed on the LCD.
This particular CO2-sensor is present in the klusbunker at RevSpace and is currently used to control the ventilation in a crude manner (by monitoring the warning LEDs on the display module). Having the CO2 ppm value available as a number allows for nice things such as logging the levels over time, announce them on IRC, show them on the LedBanner , etc.
The user manual of the Voltcraft CO-100 says "Attention! The RJ45 connection (see chapter 7, item „K“) must not be used. The connection is only intended for the manufacturer". Of course, a claim like that can only be interpreted as a challenge! :)
The CO2 meter at RevSpace has a sticker saying ZGw063RY. Unfortunately, this is not the module that is often found on the internet, with a protocol documentation.
Also, the CO2 meter at RevSpace seems to miss a bunch of components that can be mounted on the PCB, close to the RJ45 connection (possibly an RS232 chip with step-up capacitors).