AVR-Chat

Of course an external and dedicated chip is the best and easy option.
By the way, generating DTMF is not as difficult as is decoding it, so it can
be done by software.  I did it many years ago using a bare 8051 and 3.57MHz
clock, produced a mix of two several points sinewaves, mixing them by
software and finaly pumping into a R-2R 8 bits ladder, ended up in a nice
and clean waveform.  It required tricky instruction count in the sine table
reading, as well luck in a form that an easy market crystal frequency cut
allow it.  The frequency generation was just a matter of speed reading the
128 bytes sine table (180 degrees), more or less table address the routine
skip over at reading - represented a different produced frequency.  The
experiment was nice since it ended up creating enough software tecnology to
allow production of several sounds that were widely used at the next
projects.  There is nothing like a sine wave sound generation... :)

wagner.


----- Original Message -----
From: "Rogier Schouten" <r.a.schouten@student.tue.nl>
To: <AVR-Chat@yahoogroups.com>
Sent: Friday, January 02, 2004 9:40 AM
Subject: Re: [AVR-Chat] DTMF


Hi,

Take a chip for that purpose. I believe MITEL makes them. MT8870D is a DTMF
decoder, and they have encoders as well.

Rogier