Pierce Nichols wrote:
>
> On Tue, 9 Sep 1997, Alex Melven wrote:
>
> >  Hello all!
> >
> >  There is so much examples of DTMF encoding! Could enybody give me an
> > example of DTMF decoding. I need it very much. I will decode it using
> > ADC of 16c73.
>
>         Well, it's just a pair of tones, so you should just be able to do
> a FFT to get those tones out of the incoming signal.

An FFT generates too much information, requires too much RAM, and
cannot efficiently decode all of the non-harmonically related DTMF
tones. 8 simultaneously running Goertzel algorithms centered over
the 8 DTMF tones is much better. Isn't this how Steve Hardy implemented
his DTMF decoder?

The ADC will make decoding easier. However, if you are concerned
with cost then check out some theory on a 1-bit A/D converter
DTMF decoder:

http://www.interstice.com/~sdattalo/technical/theory/dtmf.html

If you are not concerned with cost, then any one of the many
DTMF decoding IC's will make your job much easier.

Scott