I'm thinking about using a MC1496 (Balanced Modulator / Demodulator). It
seems to fit my needs, once I can sum the carrier to an on/off switch, and
then just demodulate the signal with the same carrier. And all of it with
only two cheap IC per frequency!
What are your opinions?

Cheers,
 Bruno

On Thu, Dec 3, 2009 at 4:39 PM, Peter Restall <pete@restall.net> wrote:

>
> 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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