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Make: Technology on Your Time Volume 25 by Mark Frauenfelder

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SECRET-KNOCK GUMBALL MACHINE

By Steve Hoefer

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Photograph by Garry McLeod

CANDY RAPPER

Make a cute candy vending machine that only dispenses treats when you knock the secret rhythm on its front panel.

One of the best things about exhibiting at Maker Faire is giving attendees a challenge. For the 2010 Maker Faire Bay Area, I decided to combine a past project of mine, a door lock that opens only when you give a secret knock, with a standard crowd pleaser: candy.

The result was this Secret-Knock Gumball Machine, which tempted and tested the crowds at Maker Faire to guess the right rhythm and receive a treat. Since the knock was not terribly secret ...

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