How to use Perl and some inexpensive sensors to track your house's power consumption (and generation, if you have solar panels).
Covers a whole range of useful Perl topics, even if you're not interested in the specifics, including Perl on a Raspberry PI, talking to serial, USB and Bluetooth devices, the right and wrong ways to parse XML, calling an external C library, using AnyEvent, pack(), and other things. As well as a selection of cool hardware toys.