This code should be considered deprecated in favour of the following:
https://github.com/raintonr/arduino-sensors-for-loxone
Old code is left intact here for archive purposes only.
Modified version of Jiri Jasa's Arduino Pro Mini 1-Wire MQ135 interface. I would have cloned his repo but there wasn't one :(
This version basically does away with the MQ135 library in favour of simply dumping a raw analog value to the 1-Wire interface. As the Arduino Pro Mini ADC doesn't have a greater resolution than the DS2438 didn't see that being a problem. Any final value manipulation can be done in the recieving system.
Please see comments in the code, and also: