DTMF

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© 2007 Texas Instruments Inc,

Content developed in partnership with Tel-Aviv University

From MATLAB® and Simulink® to Real Time with TI DSPs

Dual Tone Multi Frequency

(DTMF)

Slide Slide 22© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

DTMF Signals

• The DTMF is a popular signaling method between telephones and switching centers

• DTMF is also used for signaling between the Telephone network and computer networks

• The DTMF signals are Transmitted over a telephone line

• Uses speech frequency signals

• DTMF signals are the superposition of 2 sine waves with different frequencies

Slide Slide 33© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

The DTMF Keypad

1209 Hz 1336 Hz 1477 Hz

697 Hz 1 2 3

770 Hz 4 5 6

852 Hz 7 8 9

941 Hz * 0 #

Slide Slide 44© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

DTMF Digits

Slide Slide 55© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

DTMF Generation

697 Hz

770 Hz

852 Hz

941 Hz

1209 Hz

1336 Hz

1477 Hz

RowSelector

ColumnSelector

Desired Digit + Dual

Tone

Slide Slide 66© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Frequency Detection

Leading Edge

Detection

DTMF Detection

x[n]Display

Convert to Display

Enable

Slide Slide 77© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

ColumnCalculation

Row Calculation

Frequency Detection

697 Hz

770 Hz

852 Hz

941 Hz

1209 Hz

1336 Hz

1477 Hz

Digit

Calculationx[n]Calculated

Digit

Slide Slide 88© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Simulation (cont.)

Selecting Digits for transmission

Slide Slide 99© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Simulation (cont.)

Detected Digits

Slide Slide 1010© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Simulation (cont.)

• The Receiver Performs:

sensing SignalRcv

New DigitBufferDigit

Edge Detected

DetectDigit

sam

ple

s

Slide Slide 1111© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Simulation (cont.)

• Digit Detection: transforms signal received to digit using the following detection blocks:

X1 … XND

etect

941 H

z

Dete

ct852

Hz

Dete

ct120

9 Hz

X1 … XN

Detect697 Hz

Detect770 Hz

Detect852 Hz

Detect941 Hz

1 2 3

4 5 6

7 8 9

* 0 #

Slide Slide 1212© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Simulation (cont.)

• Detection block operation:

– Input: X1…XN signal samples

– Output: flag to indicate whether the signal has a correlation with the frequency under detection or not

– Implementation:

» Band Pass around the frequency under detection

» Average the absolute value of the BPF output

» Comparing the average to an agreed threshold

» Flag is up the average is greater than the threshold

Detectfb = BPF

(fb-eps , fb+eps)

N

kN 1

1 ThresholdTest

flagX1…XN

Slide Slide 1313© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Real-Time Environment

• Based on the Simulation model

• R-T Implementation involves detecting the digits only

• The R-T Simulation involves a few modification to support the interface with the transmitter

Slide Slide 1414© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

PC

DSK6713

TMS320C6713

A/D

txLine In

PC(Sound Card)

DTMF Receiver

MATLAB: DTMF transmissionGUI

Detected Digitsrtdx

DTMF

Real-Time Environment (cont.)

Slide Slide 1515© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Real Time Environment (cont.)

• The DTMF signal is processed in order to overcome DC offset and to make amplitude modifications:

Slide Slide 1616© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

GUI Functionality

• Load the DSK

• Initialize RTDX

• Create DTMF samples

• Transmit them to PC Sound Card

• Display Dialed and Dtected Digits for comparison

Slide Slide 1717© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

The System

Transmitted Digit

USBSound Card

Reported Digit

)RTDX(

GUI