Created the LEGO Secret Knock Box to help the Discovery Centre in Halifax re-launch their LEGO room. Inside is an Arduino (freakin' love Arduino) listening for the secret knock combination. Once it hears the correct combo, it activates a motor and spits out a card with visual instructions to create a LEGO project.
One thing I discovered in making this was to NEVER make a paper dispensing mechanism. It is way harder than I ever thought. Many thanks to Steve Hoefer for creating the original project that became the basis for this one.