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From: paralogics!compsm!rlg@uunet.uu.net (Randy Gregor)
Newsgroups: comp.dcom.telecom
Subject: Re: Touchtone History
Message-ID: <9803@accuvax.nwu.edu>
Date: 16 Jul 90 08:01:21 GMT
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X-Telecom-Digest: Volume 10, Issue 490, Message 6 of 10


In article <9618@accuvax.nwu.edu>, boulder!boulder!bobk@ncar.ucar.edu
(Robert Kinne) writes:

> Autovon phones had (have still, as far as I know) a 4x4 key matrix
> instead of the 4x3 on conventional DTMF.

And in article <9706@accuvax.nwu.edu>, drivax!marking@uunet.uu.net
(M.Marking) writes:

> Each of the buttons makes two tones, one based on row and one based on
> column, selected so as not to be harmonics of each other. (Hence
> *Dual* Tone Multi Frequency.) The frequencies are:

> 			1209	1336	1477	1653 Hz
> 		697 Hz	 1	 2	 3	 A
> 		770 Hz	 4	 5	 6	 B
> 		852 Hz	 7	 8	 9	 C
> 		941 Hz	 *	 0	 #	 D
> 
> Most phones don't use the last column, but CCITT defines it.

Many of the commercial DTMF generator chips have (or at least did
have) the extended fourth column capability - it's just not used much
(if at all) in consumer applications.

I have a phone manufactured in 1979 with a Mostek MK5092N tone
generator (same as National Semiconductor TP5092).  To get the column
four tones, I added a SPDT switch to select between pins 5 and 9, thus
toggling the third physical keypad column between "normal" column 3
tones (1477 Hz) and extended column 4 tones (1633 Hz, according to
National's Linear Data Book).


Randy Gregor
uunet!paralogics!compsm!rlg +1 213 477 4338
Computersmith   Box 25d  Los Angeles, CA  90025