Dmitry Kiryashov wrote:
>
> 1) Does anybody write real-time DTMF
>     decoder's code (algorithm, theoretical principle) for PIC16CXX
> devices ?
>
> 2) The same question about little size real time
>     kernel (mini multitasker) for PIC16CXX ?
>
> Sorry if my questions are offtopic .
>
> Dmitry.

The problem in DTMF is decoding. One way or another you need to determine
the energy in either 7 or 8 frequency bands and then identify which
frequency in each of the two groups is dominate. There are lots of ways
that this has been attempted. (FFT, special hardware filters). The
problem of doing it in a micro like the PIC16cxx in software and meet the
decoding requirements is the need for a significant number of samples and
limited time to process them DTMF tones can be as short as 20ms. The
major software problem is the need to do signed multiplies in most of the
algothrims that I have seen.

Walter Banks
HTTP://www.bytecraft.com