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Topic: reacting to specific frequencies (Read 1 time) previous topic - next topic


Apr 17, 2012, 05:12 am Last Edit: Apr 17, 2012, 05:31 am by hilukasz Reason: 1
is there a direction someone can push me on how to build a circuit that would react to a certain sound like a clap?

was thinking of using something like this with a filter: http://www.sparkfun.com/products/9964

I have means of recording and analyzing a sound so I can find what frequency the sound is around at least. I was thinking of building a hardware or digital band-pass filter (not even sure how I would do that honestly, hah) that would only trigger a signal to arduino if that frequency was met.

I've seen suggestions in using a UM3763: http://www.chinaicmart.com/series-UM3/UM3763.html

This is only my guess at how to do this. maybe there is a better way? any ideas?
for(i = 0, i < 820480075, i++){ Design(); Code(); delay(1000); } // hellowoo.com


The main problem is that a sound like a clap is a complex waveform and is not just one frequency. That makes it difficult to recognise.
For getting at the frequency content of a waveform look to use a FFT. However that gives you in effect a list of all the frequencies and their relitave strengths. Recognising a specific sound is a lot more complex because its FFT will change over time.
While you can implement a band pass filter digitally it will not be a very high order filter due to the lack of processing power of the arduino.


Bandpass filters can have high-Q with low order though...
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That might help you, but he's right, claps are difficult to differentiate from other complex high frequency waveforms.  If all the others are low pure tones and less brief than it will be easy!  Read the datasheet within my link above.
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Implementing an envelope detector might help with capturing claps - the envelop is pretty distinctive.  Basically rapid attack and no noticeable duration before decay.  The only frequency-dependent part is choosing a time-constant for the decay - wants to be short but long enough to not count a single clap as several events.
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