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I'd like to know how a 'hand clap' switch works. You know, the kind where you *clap-clap* and the light turns on, *clap-clap* again and the light turns off.

How is the clapping sound detected? How can it be differentiated from whistling, people talking, a barking dog, ... ? Can it be another kind of sound?

What kind of components would I need to build such a sensor/switch, assuming everything works on DC?

Note: I am not interested in just buying a Velleman kit :-)

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Actually I can switch my clapper by making two barking sounds. – AndreKR Jun 15 '11 at 13:08

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The most famous example of this was "The Clapper".

See the patents for the details: 1 and 2

http://www.instructables.com/id/how-773/step1/Clapper-Circuit-Diagram/

Here's a recent hackaday post on achieving the same thing: http://hackaday.com/2011/02/07/diy-clapper/

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On a related note, you can't build this because it's patented for the next 7 years. :P – Kevin Vermeer Oct 29 '10 at 0:20
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You can't build it and sell it – Toby Jaffey Oct 29 '10 at 0:23
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It is very important to note someone with a patent can sue for building with non-commercial intent. You are stealing one sale. – Kortuk♦ Oct 29 '10 at 0:57
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This just goes to show that patents are evil and only hinder development. :) – XTL Oct 30 '10 at 19:31
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@Kortuk: It protects corporations that have lots of lawyers and make mediocre improvements to existing inventions, while they lobby for laws that disenfranchise the little guy that invents something amazing: secure.wikimedia.org/wikipedia/en/wiki/… – endolith Oct 25 '11 at 14:59
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up vote 4 down vote

What's typical for clapping hands is that it's a sudden short, but strong sound. (The sound of a barking dog may look somewhat similar, but the peaks will be longer.) A possible way to detect it is to trigger an MMV with the input signal if it's higher than a certain threshold, and see if this high level is still present when the MMV times out. If it isn't it was probably clapping hands. You'll have to experiment with threshold level and MMV time.

Not filed for patent :-)

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Isn't this what the schematic in Joby Taffey's answer does? – Federico Russo Jun 15 '11 at 10:11
it looks different. The microphone output is not used after the 555 (I think that's what it is, as monostable multivibrator). +1 – Federico Russo Jun 15 '11 at 10:50

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