Post on 18-Aug-2015
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TECHVILLA
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DTMF interfacingIntroduction to DTMF
DTMF Interfacing
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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
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The DTMF Signal
• The 12 keys on a cellphone have unique signal associated with itself.This is called DTMF.
• When call is on,the pressing of any key leads to generation of DTMF signal which is audible on other side.
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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 #
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Procedure for decoding DTMF Signal
• Dividing the signal into shorter equal time segments.
• Determining which two frequency component are present
in each time segment.
• Determining which button was pressed.
• A DTMF decoding system has two parts:
• a set of bandpass filters to isolate individual frequency
components,
• a detector to determine whether or not a tone frequency is present
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DTMF decoder using MT880
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DTMF decoder circuit
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DTMF interfacing with atmega16
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