Signal Processing Blockset 6.10

DTMF Generator and Receiver

This demo illustrates a dual-tone multifrequency (DTMF) generator and receiver. The model includes a bandpass filter bank receiver, a spectrogram plot of the generated tones, and a shift register to store the decoded digits. An alternate form of the demo, dspdtmf_audio.mdl, includes real-time soundcard audio on all platforms except Solaris™.

Contents

DTMF Generator

DTMF signaling uses two tones to represent each key on the touch pad. There are 12 distinct tones. When any key is pressed the tone of the column and the tone of the row are generated. As an example, pressing the '5' button generates the tones 770 Hz and 1336 Hz. In this demo, use the number 10 to represent the '*' key and 11 to represent the '#' key.

The frequencies were chosen to avoid harmonics: no frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the frequencies.

The frequencies of the tones are as follows:

        1209 Hz    1336 Hz    1477 Hz

697 Hz    1          2          3
770 Hz    4          5          6
852 Hz    7          8          9
941 Hz    *          0          #

DTMF Receiver

Running the Demo

When you run the simulation, the spectrogram of the received tone will be constructed. If you use the version of the model designed for audio hardware, the received tone is played through the system soundcard. The detected dialed numbers will be shown on the numeric display scope. The following parameters can be adjusted:

Demo Model

Available Demo Versions

Floating-point version: dspdtmf.mdl

Floating-point version using audio hardware: dspdtmf_audio.mdl