On Wed, 2 Dec 2009 17:51:34 -0200, Bruno L. Albrecht wrote:

> Hi,
> I'm trying to separate 3 frequency components from an analog signal. The
> original signal is composed by the sum of 3 frequencies (1500, 4000 and
> 10200 Hz) and some noise. The objective is to separate only those 3
> frequencies and evaluate their magnitudes. I thought about lots of ways of
> doing it, but couldn't get an effective one.
> Any ideas?
> 
> Cheers,
>  Bruno
> 

If there were two tones, perhaps a PLL.  But I think this would be a nice
application for the Goertzel algorithm if you're willing to use DSP.  The
dsPICs would easily be able to do this - in fact, I think wikipedia has a
C implementation as well as a description (for DTMF decoding).  I don't know
how the majority of the maths work, but the implementation is straightforward
enough to follow.  I suppose your solution will also depend on how much noise
you have/anticipate (and the frequency if it's from a known source; aliasing
may be a problem), but sounds like a good application for Goertzel anyway.
Would certainly be an interesting project.

Regards,

Pete Restall
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