> I have done DTMF decoding using just a zero-cross detector and a 20MHz
> PIC.  Depending upon whether tone generation is required as well, the
> routine uses about 40-70% CPU time [it has two parts: an interrupt routine
> that uses about 40-50% CPU, and a calculation routine that needs to be
> called about 60 times/sec].
>
> Unfortunately, because I developed the routine for my employer I cannot
> release it on the net, at least not presently.  On the other hand, I will
> say that it is possible to do a good job of detecting DTMF or other such
> tones, using a PIC, even in the presence of other audio (such as dial
> tone).  My routine looks for eight tones simultaneously, and is selectable
> between two groups of eight (one set up for DTMF, one for call-progress
> and special tones).

Would you say your design worked better than an off the shelf DTMF chip?

Gus Calabrese

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