Area : ¸® PIC- ¬

Date : Sun Jun 29, 19:50                                                       
From : Ian Cameron                                             2:4600/65
Org  : The Open University                 
Subj : DTMF                                                                  
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997 9:30:14 -0500
h
MTP
 25

> Can anyone furnish me with a list of the frequencies which correspond to
> those
> used in 'tone' dialling; 0-9, #, * ?

There's a DTMF FAQ available at:

http://www.paranoia.com/~filipg/HTML/LINK/LINK_IN.html#LINKIN_004

>From part of that FAQ:

3. Short introduction to DTMF

DTMF means: Dual Tone Multi-Frequency, There is no baseband
multiplexing done on DTMF signals. The signal generated by a DTMF
encoder is a direct algebraic summation, in real time, of the
amplitudes of two sine (cosine) waves of different frequencies. i.e.
pressing '1' will send a tone made by adding 1209 Hz and 697 Hz to the
other end of the line.

(From the Editor)

Here's a more detailed explanation of what DTMF is:

Q: What frequencies do touch tones use for which numbers?

A: The touch tone system uses pairs of tones to represent the various
keys. There is a "low tone" and a "high tone" associated with each
button (0 through 9, plus * (star) and # (octothorpe or pound symbol).
The low tones vary according to what horizontal row the tone button is
in, while the high tones correspond to the vertical column of the tone
button.

The tones and assignments are as follows:


          1     2     3     A  :  697 Hz

          4     5     6     B  :  770 Hz
                                           (low tones)
          7     8     9     C  :  852 Hz

          *     0     #     D  :  941 Hz
        ----  ----  ----  ----
        1209  1336  1477  1633 Hz
               (high tones)

or:


          1209 Hz 1336 Hz 1477 Hz 1633 Hz

                   ABC     DEF
697 Hz      1       2       3       A

           GHI     JKL     MNO
770 Hz      4       5       6       B

           PRS     TUV     WXY
852 Hz      7       8       9       C

                   oper
941 Hz      *       0       #       D

or:


    1  697+1209
    2  697+1336
    3  697+1477
    4  770+1209
    5  770+1336
    6  770+1477
    7  852+1209
    8  852+1336
    9  852+1477
    0  941+1336
    *  941+1209
    #  941+1477
    A  697+1633
    B  770+1633
    C  852+1633
    D  941+1633

When the 4 button is pressed, the 770 Hz and 1209 Hz tones are sent
together. The telephone central office will then decode the number
from this pair of tones.

The tone frequencies were designed to avoid harmonics and other
problems that could arise when two tones are sent and received.
Accurate transmission from the phone and accurate decoding on the
telephone company end are important. They may sound rather musical
when dialed (and representations of many popular tunes are possible),
but they are not intended to be so.

The tones should all be +/- 1.5% of nominal. The high frequency tone
should be at least as loud, and preferably louder than the low
frequency. It may be as much as 4 db louder. This factor is referred
to as "twist." If a Touchtone signal has +3db of twist, then the high
frequency is 3 db louder than the low frequency. Negative twist is
when the low frequency is louder.

---

Hope this helps.

Cheers, Ian.


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 * Origin: ### Internet-Eudora-Fido-Gate ### (2:4600/65)