Part 3: The software side
Finally got round to tidying up the code. There's the arduino sketch which powers the lights, and a java application that runs in the background on the server, reads the server logs and will produce the serial commands that are sent to the arduino.
It uses the RXTX serial library, and the code itself is available on GitHub at https://github.com/darkmidnight/UnrealLANBox
There's still room for plenty of improvement, like getting the lights to flash when a flag has been taken.
I also put together a video showing the build process and a demo of it in action, see below