There's a few projects out there that can listen to a pattern of knocks and take action on the results, and the following example by Michele Marolla is a simple and easy to understand version. Using a piezo sensor to detect the knocks, the system can be taught new patterns to remember, control a servo (or other device) if the correct pattern is entered - and also play back the sequence to ensure the creator understands what needs to be done in the future. The project is demonstrated in the following video:
Although only a bare version, it's all there so you can fit the parts to your own enclosure. To find out more, visit Michele's project page. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
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