Working Of DTMF (Dual Tone Multi Frequency) Technology and Its Applications

DTMF is a type of a signaling system, used to send the information through the phone lines. The dual tone multi-frequency is the signal of a phone company, it generates when you press an ordinary telephone touch keys. In the united states or in other places, it is known as a touch tone phone dialing. Mostly this technology is used in the mobile phones with the right techniques and decoded DTMF signal is used in the robotic microcontrollers to increase the robot performance to a certain action. The usage of DTMF technology in applications is a not new technology, but the purpose of this paper is to address a new approach to this. In this article, we will learn about the working and applications of the DTMF.

What is a DTMF?

The DTMF is a signaling system for recognizing the keys or on the dialed number of a push button or simply we can say it as a DTMF keypad. It is a combination of two sine wave tones to constitute a key. The tones are called as a rows & Colum frequencies and they are represented on the DTMF keypad. DTMF switches ON the long distance signaling to the dialed number through the voice frequency.

In the dual tone multi-frequency, if we press any key on your phone, then it generates two tones of specific frequencies, the first specific frequency is a high frequency of tone and the second one is a low frequency of the tone. The following table shows the signals that you send when you press your touch tone phone keys.

Digital	Low Frequency (Hz)	High Frequency (Hz)
1	697	1209
2	697	1336
3	697	1477
4	770	1209
5	770	1336
6	770	1477
7	852	1209
8	852	1336
9	852	1477
0	941	1336
*	941	1209
#	941	1447

DTMF Working Principle

The dual tone multi-frequency uses eight frequency signals which are transmitted in a pair to produce the sixteen numbers with the symbols & letters. The following table shows the eight numbers, symbols and the letters from A-D. Let us consider that, if we press any key it will produce the highest & a low tone for each of two frequencies. By using the HT9170B IC, digital counting technique these two tones are decoded to determine the key which should be pressed.

	1209 Hz	1336 Hz	1477Hz	1633Hz
697Hz	1	2	3	A
770Hz	4	5	6	B
852Hz	7	8	9	C
941Hz	*	0	#	D

In the phone, the tone is filtered with the help of the operational amplifier. If the output is high voltage then the pin 10 enables output of D0, D1, D2, & D3 which are decoded the outputs of IC. The DV pin 15 is an output pin which is set at high by using the IC after all the pins from D0-3 are filled and the action will show the data is valid and useful. To check the tone of authentication we should use the RT/GT and EST monitor. If the tone is very long the steering control of these pins will automatically fill the latches of D0-3 pins. After this, it will set DV pin on high to indicate the output is ready to use by the microcontroller.

By this process, the DTMF decoder can decode the 16 different types of key tones in the form of 4-bit binary decode output. The following table shows that four-bit binary decoder for each key tone and number.

Digit	OE	D0	D1	D2	D3
1	H	1	0	0	0
2	H	0	1	0	0
3	H	1	1	0	0
4	H	0	0	1	0
5	H	1	0	1	0
6	H	0	1	1	0
7	H	1	1	1	0
8	H	0	0	0	1
9	H	1	0	0	1
0	H	0	1	0	1

Applications of DTMF

• The DTMF tones are mainly used at the telephone switching centers, to detect the dialed numbers
• These are used in the terrestrial stations to switch on and switch off the remote transmitters
• DTMF is also used in the call centers, IVR systems, and security systems
• This system can be used in the industrial applications

Advantages of DTMF

• A fast response will achieve
• With low price, the DTMF can be designed
• It can control the electrical devices wirelessly
• The consumption of power is less
• The construction of DTMT is very easy

In this article, we have discussed working with DTMF technology and its application. I hope by reading this article you have gained some basic knowledge & information about the DTMF technology. If you have any queries about this article or about the electronic and communication projects for engineering students, please feel free to comment in the below section. Here is the question for you, what are the functions of the dual tone multi-frequency?