Slide 1

DTMF & ITS APPLICATION

Submitted to:- presented by:Mrs.Anita chopra amit kumar singh (Asst. proff) Sec-B1,Roll No-3

1Introduction History Working of DTMFDTMF digits waveformGeneration of DTMFDTMF DetectionFrequency DetectionApplicationAdvantage and DisadvantageReferences

CONTENTSINTRODUCTION DTMF stands for Dual Tone Multi Frequency.Dual-tone multi-frequency signaling(DTMF) is used for telecommunication signaling (telephones and voice mail systems). Dual Tone Multi Frequency is a technology that can be used to send information through phone lines.

It uses speech frequency signals.The version of DTMF that is used inpush-button telephonesfor tone dialing is known asTouch-Tone.Allow users and devices to dial at much higher rate because of the uniformity of numbers.DTMF is also used for signaling between the Telephone network and computer networks.Numbers and commands issued from a keypad.DTMF signals are the superposition of 2 sine waves with different frequencies.Allow users and devices to dial at much higher rate because of the uniformity of numbers.

HISTORY DTMF was the driving technology implemented in push-button telephones. Push-buttons in telephony originated around 1887 with a device called the micro-telephone push-button. This use even predated the invention of therotarydial byAlmon Brown Strowger in 1891.

push-button phone in the 1970s with 12 keys.

Modern push-button telephoneWORKING OF DTMF

Set of high frequencies

Set of low frequencies

Button click generates a combination

8 => S(852, 1336)

Each digit corresponds to a high frequency and a low frequency - Both are transmitted simultaneously Works by sending two sinusoids for each symbol pressed on the telephone keypad.The tones are divided into two groups:Low group: 697 Hz, 770 Hz, 852 Hz, 941 HzHigh group: 1209 Hz, 1336 Hz, 1477 Hz.The DTMF system uses eight frequency signals transmitted inpairs to represent sixteen numbers, symbols and letters. The HT9170B IC, using digital counting techniques, decodes these two tones to determine the key being pressed.

Special tone frequencies National telephone systems define additional tones to indicate the status of lines, equipment, or the result of calls with special tones. Such tones are standardized in each country and may consist of single or multiple frequencies. Most European countries use a single precise frequency of 425Hz, where the United States uses a dual frequency system.

Event Low frequency High frequencyBusy signal(US) 480Hz 620HzRingback tone(US) 440Hz 480HzDial tone(US) 350Hz 440Hz

DTMF DIGITS WAVEFORMGENERATION OF DTMF697 Hz770 Hz852 Hz941 Hz1209 Hz1336 Hz1477 Hz Row Selector Column SelectorDesired Digit Dual Tone Frequency Detection Leading Edge DetectionDTMF DETECTIONx[n]DisplayConvert to DisplayEnableColumnCalculationRow CalculationFrequency Detection697 Hz770 Hz852 Hz941 Hz1209 Hz1336 Hz1477 Hz DigitalCalculationx[n]Calculated Digit13Signal to noise ratio (SNR)Quantity used to describe the quality of signal.Ratio of magnitude of wanted signal to unwanted signal expressed in dB.The transformation from dB to noise power is done following way:

Where Px = Signal Power Pw = Noise Power

Output of DTMF toneDialled noSignal powerNoise powerSNR [dB]11.00700.014818.327921.00370.016517.8322208360991.00360.014818.3160248300091.00360.016717.780900233246860431.00560.016217.9198Test Results from Different Dialled NumbersAPPLICATION OF DTMF DTMF BASED HOME APPLIANCE CONTROL

Mobile operated car using DTMFBLOCK DIAGRAM OF DTMF BASED HOME CONTROL APPLIANCES TELEPHONEDTMFMICROCONTROLLERDC POWER SUPPLYRELAYRELAYRELAYULN2003BLOCK DIAGRAM OF Mobile operated car using DTMFTELEPHONEDTMFMICROCONTROLLERDC POWER SUPPLYMOTOR1MOTOR 2ADVANTAGES OF DTMFCan be controlled from any part of the world.Very compact programming.Easy to operateCan avoid obstacles and propagateDISADVANTAGES OF DTMF In the event of malfunction the damage can be severe.referencesWikipedia, the free encyclopedia.http://www.alcatel-lucent.com/bstj/vol39-1960/articles/bstj39- 1-235.pdfhttp://www.mesi.net/MESiWeb/Digit%20Detector%20Preformance%20data.html http://www.tech-faq.com/abcd.shtml The essential guide to telecommunications. Prentice Hall PTR, 2002.

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