Path: utzoo!attcan!uunet!husc6!rutgers!bellcore!faline!thumper!pff
From: pff@thumper.bellcore.com (Peter Ferris)
Newsgroups: sci.electronics
Subject: DTMF (Touch-Tone) --> RS-232 Conversion
Keywords: DTMF, RS-232, Touch-Tone, Please Help!
Message-ID: <1441@thumper.bellcore.com>
Date: 25 Jan 89 16:17:35 GMT
Organization: Bell Communications Research
Lines: 31

Greetings,
Excuse me if this is something that's been asked 583 times already, but I'm
attempting to build a DTMF (Touch-Tone) --> RS-232 converter.  I've seen the
units in the magazines for $90, but it seems to me that's about $75 too much!
Does anybody have any experience in this area?

My specific questions are:

1)  I guess the choices seem to be the SSI-202 (Radio Shack = c.$13.00)  or the
SSI-204 IC's.  Who makes these (Samsung?), and what is the difference between
them?

2) How should I (or SHOULD I) control baud rate; eg; dipswitch and/or software?
Or would it be simpler / cheaper / "better"  to decide on a "fixed" baud rate
(would 300 baud be fast enough for a very rapid burst?)?

3) I need to decode all <16> characters (0-9, A-D, # & *).

4) The circuit should be somewhat "forgiving" in that the DTMF will be decoded
from a variety of audio sources, ie; scanner, handie-talkie, vcr, and other
audio sources - but the audio could have static or other artifacts in it.

Permit me to add that this project is what we call a "G-Job" - it's for my own
personal pleasure / experimentation.  If anyone has any suggestions, comments
or schematics on this rainy day project I'd sure appreciate hearing from you.  
Best bet is Internet E-mail.

Many Thanks in Advance,

Pete Ferris, N5KBD
pff@thumper.bellcore.com