I whipped this up Friday afternoon after a costume party invite. It normally says "LANE ENDS MERGE RIGHT" and can be hacked to say "CAUTION! ZOMBIES! AHEAD!!!"
I used an RBBB arduino board from Modern Devices to control an 8x32 LED display from Sure Electronics. When you open the access panel, the blinking green light indicates normal operation. To hack the sign you must figure out which of six bolts is the key and clamp an alligator clip to it. When the correct bolt is found, the light will flash blue quickly and then continue flashing red while the hacked message is displayed. The key bolt is randomly picked each time the hack is disengaged.
Thank you. I was having a time trying to come up with a quick costume when I spied that display and figured I'd better go with what I know.
The 'enclosure' is a cardboard box, painted black and lined with tinfoil. I cut out a hole for the display and secured it with a dab of hot glue on the corners. The front flap secures with a pair of neodymium magnets. The ckt is built on a breadboard and ziptied inside the box. A piece of plexiglass fit in a slot on the breadboard giving me a mount for the hacking terminals.
My apologies for the crappy video quality; I plan to fix that this weekend.