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'[PIC]: bandpass was [PIC]: The tintinnabulation '
2000\11\08@135359 by Lawrence Lile

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Hmmmm.... If you can do a low pass filter in software with such ease, what
about a bandpass filter in software?  I have another project where I need to
pick out a single frequency among a noisy signal, and I was dreading the
extra $$$ involved in a bunch of tighly tuned analog filtering.

-- lawrence

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2000\11\08@142112 by Scott Dattalo

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On Wed, 8 Nov 2000, Lawrence Lile wrote:

> Hmmmm.... If you can do a low pass filter in software with such ease, what
> about a bandpass filter in software?  I have another project where I need to
> pick out a single frequency among a noisy signal, and I was dreading the
> extra $$$ involved in a bunch of tighly tuned analog filtering.

You can look at:

http://www.dattalo.com/technical/theory/dtmf.html

For the theory of decoding DTMF, which amounts to plucking out tones. However,
the algorithm is suited torwards a yes/no result.

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2000\11\08@145226 by David VanHorn

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At 12:29 PM 11/8/00 -0600, Lawrence Lile wrote:
>Hmmmm.... If you can do a low pass filter in software with such ease, what
>about a bandpass filter in software?  I have another project where I need to
>pick out a single frequency among a noisy signal, and I was dreading the
>extra $$$ involved in a bunch of tighly tuned analog filtering.

If you sample exactly X times per wave of the desired signal, and average
the signal into those X bytes in ram, then you'll end up with a copy of the
waveform (if it exists). The max and min values will be near zero if not.

How you average it in will set the bandwidth of the filter, and it's
response time.
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