How a "secret knock" device works and how to build one

Come see how a "secret knock" device works and learn the techniques for creating very effective knocks. You will see how it works on the gum ball machine (Make Volume 25), plus how the same software/hardware can be adapted to other needs.

What inspired you to make this project?:
Make Magazine vol 25 inspired my granddaughters to build a secret knock gumball machine. Their school in San Mateo held a recent Mini Maker Faire (although they weren't allowed to use that name) where they displayed their make projects, notably a secret knock gumball machine and how to make led flashlights. Their tables were the hit of the evening and we all noticed how much difficulty was experienced by a large number of participants in understanding 1) how the machine worked, 2) how the knocks were interpreted inside the Arduinos, and 3) how little recognition was evident regarding how the timing of musical notes was the basis for the machine. We plan to show folks how to understand and use this technology to build something of their own.