So, exams are finally over and I've had time to get playing with something again. Some friends bought me a NERF Vulcan for my birthday (cheers!) and of course I had to mod it up. The gun itself is now running off a 3-cell lipo pack, which about doubles the rate of fire, and has three ammo belts chained together to give 74 rounds in one continuous burst of fire.
I then hooked up an Arduino and servo motor to a series of cabletied pencils, which can pull the trigger on command. The Arduino and a USB webcam then connect to a laptop which is running motion and a small python script which interfaces to the Arduino and plays sound clips from Portal turrets when motion is detected/no longer detected.
The whole thing works very nicely, shooting down anyone who walks into my room with a rapid burst of darts, and terrifying them with the portal turret sounds.
Check out flickr for more photos!
I modified Principia Lab's servo code from here and motion and Portal turret sounds from Valve's Portal and the code below for controlling motion and the arduino and playing the sound files: