Steve Ocepek, Director of Security Research, Trustwave SpiderLabs presented this talk at Defcon 19 (2011). He harkens back to the days of blinking modem lights, and demonstrates how to create a modern day “blinking light” network monitoring device using the Arduino Uno along with itead Studio’s Color Shield. Dubbed the cerealbox, this design interfaces with your PC via USB to obtain network data which the Arduino interprets and converts for the Color Shield display.
You can visit the Defcon website to download the 36 page PDF on this talk. The Arduino code can be found among a wealth of other conference material on the Defcon 19 DVD which is available as a 1.7 GB download from the Defcon archive.