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Dual-tone multi-frequency signalling HABEEB ALI

10011P0409,ECE(IDP) JNTU COLLEGE OF ENGINEERING

HYDERABAD,500085

ALI.HABEEB1@GMAIL.COM

Abstract Here I described dual tone multiplefrequency operation and a small program to showhow it generates two combination of sinusoidalsignals.Concept behind that and its advantagesalso been described.

keywords DTM ! "#$%#&C'

I. INTRODUCTION

Dual tone multiple frequency is used in

telecommunication, where dialin of num!er

"also si nalin such as redialin # is done !y dual

frequency ,for e for each $ey there !e alloted

com!ination of two frequencies.

DU%& TON' (U&TI)&' *R'+U'NC has

!ecome -ery popular has replaced pulse dialin

system in telecommu nication world.

It also finds application in personal computers,remote

sensin systems etc.

In Telecoomunication it is used for si nallin ,such as

!usy tone,unnum!ered tone,timin tones etc.

It operates in international reco nised

standards,it means some fi ed frequency alloted for

each num!er we dial.so that decodin circuit which

we use remain same for all instruments .'ach num!er is i-en !y com!ination of frequencies.The -ersion of DT(* that is used in push !utton

telephones for tone dialin is $nown as Touch-Tone .

DI%&IN/

0. 1I2TOR

There are two dialin system one is loop

dialin other is DT(*.3elow circuit that are used old telephone

system.whichare electromechanical .

4hen you lift the phone.circuit ets closed

few dc amp current flows from central office

Dial is arran ed in such such that closin and

off of switch i.e., pulses represents di it you

ha-e dialled.

Upper limit of 56 pulses for sec is there for

each di it.so eac pulse on time is 566ms.

On and off period is not constant it may !e

different in differnt countries

for e 7

http://en.wikipedia.org/wiki/Push-button_telephonehttp://en.wikipedia.org/wiki/Push-button_telephonehttp://en.wikipedia.org/wiki/Push-button_telephonehttp://en.wikipedia.org/wiki/Push-button_telephone

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U2% on time89:ms

off time8;;ms

in ratio 075.

this sytem is more costly ,less efficient,less

relia!le and less efficienct.

2o we mo-e to electromechanical systems.4hich is

DT(*.

;. DT(*

It uses < different frequencies which on com!inationi-es 59 different si nallin .

2o,$eypad has 59 different sym!ols i.e., num!ers and

some alpha!ets which are represented in the form of

matri of order =!y=.

This idea was i-en !ell la!oratories .

It uses low frequency for rows and hi h frequency forcolumns.2chematic dia ram is shown in fi ure

*requency used in DT(* has some properties 7 all frequency are different none of the frequency is inte er multiple of

othe frequencies and they are not com!ination of any other

frequencies that is sum and difference willnot produce other frequency

*requencies used here may not -ary 5. from theirnominal frequencydifference !etween hi h and low frequency wil !e notmore than ;d!.

The sym!ols ?,@%,3,C,D $eys are used for repeatercontrol,remote !ase operation and otherfor sometelecommunication purposes.

' 7@ is used for dialin

If $ey is 5 pressed it produces a superposition of twosinusoidals accordin to their frequency alloted inDT(*

Aey 5 produces 9B: and 506B sinusoidal cur-es.

This concept can !e !etter understood !y a pro ram

which can !e easily implemented in (%T&%3 .

This is for 5 to B no s and same can !e pro rammedfor =!y = matri .

>> pro ramclcclose allclear allt=0:0.0001:0.0099length(t)enter nos !n a ro" three t!#es

$or !=1:%n=!n&'t( enter no )!$ n== * +rea,en-!$ n==1 $1= 9/ $ =1 092 $re3'enc!es!n -t#$ cons!-er!ng onl4 no s$re3'enc4 en-!$ n== $1= 9/ $ =1%% 2en-

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!$ n==% $1= 9/ $ =15//2en-!$ n==5 $1=//0 $ =1 092en-

!$ n==6 $1=//0 $ =1%% 2en-!$ n== $1=//0 $ =15//2en-!$ n==/ $1=76 $ =1 092en-!$ n==7 $1=76 $ =1%% 2

en-!$ n==9 $1=76 $ =15//2en-$!g're (1) &lott!ng all those8=s!n( $ &! t) s!n( $1 &! t)2 !$ !==1 &lot(t 8 r ) hol- on en- !$ !== &lot(t 8 + ) hol- on

en- !$ !==% &lot(t 8 g ) hol- on en-en-

!n&'t=1 5

5. CI;C

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6. DT(* R'C'I 'R

Usin si nallin plan as descri!ed !y C')T recei-er

-alidates tone frequencies and decodes sees that they

are in accepta!le frequency de-iation.then after that it

oes to power detector whic performs operations

suchas toneonset ,thresholdin etc

. %))&IC%TION2

DTMF tones are thus mainly used

At the telephone switching centres for

detection of dialled/called number.

They are also used !y certain radio and ca!leT networ$s.These networ$s use DT(*

tones to si nal a networ$ station or local

ca!le operator when a local ad-ertisement is

to !e inserted or for station identification. In

broadcasting, this is known as local

insertion. DTMF tones were also used by terrestrial

stations for turning on and shutting off

remote transmitters.

DT(* tones are sometimes used in caller ID

systems to transfer the caller ID information.

/. CONC&U2ION

In this DT(* concept ha-e !een e plained with a

pro ram which can !e easily -erified in (%T&%3.

The main idea to understand $ey !ehnd DT(* and to

further de-elop and to apply this in -arious fields in

technolod y in !etter approach.

R'*'R'NC'2

E5F Crai mar-en,/enaral purpose of DT(*, Te as

Instruments.E0FDT(* format 7 http7GGwww. ena-e.comGdtmf.html

E;F DT(*7 from

http7GGwww.!oondo .comGtutorialsGdtmfGdtmf.htm

E=F DT(* 2I/N%&&IN/,4IAI)'DI%

http7GGen.wi$ipedia.or Gwi$iGDualHtone multiH

frequency si nalin

EJF DT(*7from !lo

http7GGwww.en ineers ara e.comGtutorialsGdtmfHdualH

toneHmultipleHfrequency

E9F%pplication of dtmf,)D*

http7GGwww.Kilo .comG

http://en.wikipedia.org/wiki/Caller_IDhttp://www.genave.com/dtmf.htmlhttp://www.boondog.com/tutorials/dtmf/dtmf.htmhttp://www.engineersgarage.com/tutorials/dtmf-dual-tone-multiple-frequencyhttp://www.engineersgarage.com/tutorials/dtmf-dual-tone-multiple-frequencyhttp://en.wikipedia.org/wiki/Caller_IDhttp://www.genave.com/dtmf.htmlhttp://www.boondog.com/tutorials/dtmf/dtmf.htmhttp://www.engineersgarage.com/tutorials/dtmf-dual-tone-multiple-frequencyhttp://www.engineersgarage.com/tutorials/dtmf-dual-tone-multiple-frequency