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DTMF Based Engineering Projects

The first DTMF was developed by the Bell System in USA; it became popular under the brand name Touch-Tone that uses in push-button based telephones delivered to telephone customers in 1963.The acronym of the DTMF is Dual Tone Multi Frequency; it is the source for telephone system. The term DTMF is the generic name for touch tone. The touch tone of the smart phone is a DTMF generator that generates DTMF tones when you press the buttons.


DTMF signaling system is used to recognize push buttons or keypad. The telephone systems in olden days used pulse dialing and later it was replaced by a multi frequency dialing system called DTMF. This system is a multi-frequency tone dialing system uses a keypad in mobile sets and telephones to convey the input dialed by the caller.

DTMF allows long distance signalling of dialled numbers in the range of voice frequency over telephone lines. This has removed the involvement of telecom operator between the callee and the caller and thus develops automatic dialling in the telephone switching centers.

DTMF uses a blend of two sine wave tones to signify a key. The sine wave tones are called row and column frequencies as they communicate to the layout of the keypad of the telephone. A DTMF produces a sinusoidal tone which is a combination of the frequencies of row and column. Here, the low group frequencies are row frequencies, whereas the high group frequencies are column. DTMF tones can signify one of the symbols on the keypad. This is corresponding to 4 bits of data, which is also named as a nibble.

When you push the buttons on the keypad, it generates two tones: row and column tones. These two tones recognizes the pressed key to any device you are controlling. If the keypad is on your phone, then the equipment in the central telephone office identifies the inputs that have been given by these tones, and connects the call accordingly.

If anyone using a DTMF to control the equipment, the two tones can recognize the device that needs to be controlled, as well as which function they want to execute.

• If you press the number 1 on the keypad, then it generates the tones in the range of frequencies 1209Hz & 697 Hz.
• If you press the number 2 on the keypad, then it generates the tones in the range of frequencies 1336Hz and 697Hz.
• For both 1 and 2 digits, the 697Hz tone is similar, but it takes a couple of tones to make a number and the decoding of the device know the variation between the two frequencies that both would complete a digit 1and 2.


DTMF tones are mainly used in telephone switching centers for finding dialed or called number. And also in a particular cable TV and radio networks to signal a local cable operator and a network station for station identification. DTMF is used in broadcasting called as local insertion and also in terrestrial stations for turning ON and OFF remote transmitters.

This category consists of DTMF projects with abstract, PPT and block diagram which can be downloaded by the students. Here is a list of collection of DTMF based projects.


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