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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