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Dtmf Encoder And Decoder Using Labview

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2002 Annual Conference


Montreal, Canada

Publication Date

June 16, 2002

Start Date

June 16, 2002

End Date

June 19, 2002



Conference Session

Instrumentation Poster Session

Page Count


Page Numbers

7.448.1 - 7.448.10



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Paper Authors

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David Loker

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NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract

Main Menu Session 2559

DTMF Encoder and Decoder using LabVIEW

David R. Loker, P.E. Penn State Erie, The Behrend College


In this paper, a laboratory experiment is presented for a senior technical elective course in telecommunications in the Electrical Engineering Technology Baccalaureate program at Penn State Erie, The Behrend College. For this experiment, students use LabVIEW and a PC-based data acquisition (DAQ) system to design a dual-tone multifrequency (DTMF) encoder and decoder. The user input for the encoder is from a 12-pushbutton external keypad used to simulate the touch-tone telephone keypad. The output of the decoder is a 7-segment display used to indicate the depressed pushbutton. The encoder and decoder are each implemented on a separate PC-based DAQ system. They are interconnected with a signal wire and a ground wire, simulating the telephone line.

I. Introduction to the Telecommunications Systems Class

A senior technical elective course in telecommunications is offered as part of the Baccalaureate degree in Electrical Engineering Technology at Penn State Erie, The Behrend College. There are two prerequisites for this course. The first prerequisite course is a junior level communications systems course which emphasizes an introduction to analog communication techniques. The second prerequisite course is a junior level measurements and instrumentation course which introduces LabVIEW and data acquisition. This senior telecommunications systems course emphasizes voice and data communicat ions techniques. There are seven laboratory experiments covered within this course, and all of the experiments utilize LabVIEW. The dual-tone multifrequency (DTMF) encoder and decoder experiment is the second experiment within the course and covers three weeks of the semester.

In order to complete the objectives for this experiment, the students are presented introductory information about dual-tone multifrequency (DTMF) and about the technique for simulating the DTMF encoder and decoder using a data acquisition (DAQ) system. Based upon the students' previous knowledge about LabVIEW and data acquisition, they are asked to design the hardware and software needed to demonstrate a working DTMF encoder and decoder. The hardware required for this experiment consists of a keypad to simulate the function of the telephone keypad and a 7-segment display for displaying the properly decoded pushbutton. The software required for this experiment consists of developing the algorithms necessary for encoding and decoding the depressed pushbutton. After demonstrating a working system, each student group provides a lab report discussing their results.

II. Introduction to DTMF

A dual-tone multifrequency (DTMF) waveform is generated when a pushbutton on a telephone keypad is depressed. 1-4 This is also referred to as touch-tone dialing. The arrangement of the keypad is shown in Figure 1.

"Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright ã 2002, American Society for Engineering Education"

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Loker, D. (2002, June), Dtmf Encoder And Decoder Using Labview Paper presented at 2002 Annual Conference, Montreal, Canada. 10.18260/1-2--10145

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