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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 :-)

Vincent Van Den Berghe
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3 Answers3

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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 :-)

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

See the patents for the details: 1 and 2

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


(source: instructables.com)

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

Glorfindel
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Toby Jaffey
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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 00:20
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    You can't build it and sell it – Toby Jaffey Oct 29 '10 at 00:23
  • You can still build it for "research purposes" but I believe patents would prevent you from selling it or even distributing it for free. (i.e. giving it to a friend.) – Thomas O Oct 29 '10 at 00:28
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    Then how is it distributed as a kit by Vellman? – Kevin Vermeer Oct 29 '10 at 00:31
  • @Joby You can still get in trouble even if you aren't selling it @Thomas do you have any sources that say you can still build if for research purposes? @reemrevnivek if I were to guess, they either use a different method or they have a license to use the technology. – Kellenjb Oct 29 '10 at 00:45
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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 00:57
  • The idea for patents is that people can learn from your product; that's why you have to publish everything out in the open. – Thomas O Oct 29 '10 at 08:43
  • Thanks. You wouldn't happen to have any other links that aren't a wall of text and feature some schematics? :-) – Vincent Van Den Berghe Oct 30 '10 at 16:11
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    This just goes to show that patents are evil and only hinder development. :) – XTL Oct 30 '10 at 19:31
  • There are two sides to that @XTL, it also protects those that invent something amazing. I have quite a few problems with the patent system, but there are some things it does correctly. – Kortuk Oct 30 '10 at 20:25
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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: https://secure.wikimedia.org/wikipedia/en/wiki/America_Invents_Act#First_to_file_and_grace_period_2 – endolith Oct 25 '11 at 14:59
  • If you look at this schematic, but don't build it, you could be sued. By not building it, you do not violate the patent. Thereby, you are taking away business from patent lawyers. – Kaz Apr 01 '13 at 03:55
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The response of a hand clapper is basically the impulse response of your transfer function. Since the response is the transfer function itself, you can design your transfer function to suit your needs accordingly. The best way is, to sample your sound analyzer input and interface it with a digital signal processor and then go crazy with discrete laplaces and FFTs.

ubuntu_noob
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  • This really doesn't make any sense. – Dave Tweed Mar 03 '14 at 05:29
  • why? Can't a hand clap response of a system be used as an impulse response? We've done modelling problems like that in college before, in DSP... – ubuntu_noob Mar 03 '14 at 05:31
  • Yes, hand claps are sometimes used to estimate the impulse response of, say, a reverberant room. But this has absolutely nothing to do with how a clap-operated switch works. – Dave Tweed Mar 03 '14 at 05:35
  • No, I was talking about differentiating a hand clap signal from other discrete impulses, using DFT of the signal where the hand clap can be correlated to other hand claps and then a tuned correlation can be achieved, the other sharp signals, like dog barking or engine revving could be differentiated. I have seen one group display a project on that... – ubuntu_noob Mar 03 '14 at 05:44
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    You are waaay over-thinking this ... – Dave Tweed Mar 03 '14 at 05:58
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    Generally, when answering an old question (2010) it's expected that you spend some time in crafting a very good answer that is better than the existing ones. While yours is valid, it doesn't tell a lot to the reader, so doesn't add much value to the post. – clabacchio Mar 03 '14 at 06:49
  • Okay, I'll delete mine if you want... – ubuntu_noob Mar 03 '14 at 06:52
  • It doesn't matter about this answer, but please consider it in the future, because it ends up bringing old questions to the top page in spite of newer questions. Do it only if you think it's really worth it. – clabacchio Mar 03 '14 at 15:32
  • Okay. Apologies for the answer. I'll take care in the future. I had no idea about the old questions popping up again. You have my word, I'll consider... – ubuntu_noob Mar 03 '14 at 17:04