DTMF - Dual Tone Multi Frequency Signalling
Posted On Tuesday, February 12, 2008 at at 11:12 PM by Murali SrinivasanDual Tone Multi-Frequency, or DTMF is a signaling method for instructing a telephone switching system about the telephone number to be dialed.DTMF tones are also in caller ID systems to transfer the caller ID information.The DTMF system uses eight different frequency signals transmitted in pairs to represent sixteen different numbers, symbols and letters used are #, *, A, B, C, and D.
DTMF Keypad Frequencies.
DTMF Keypad Frequencies.
The DTMF keypad is 4×4 matrix, each row representing a low frequency, and each column representing a high frequency. While pressing a key (say '1' ) will send a sinusoidal tone of the two frequencies (697 and 1209 hertz). The original keypads have levers inside, so each button activates two contacts. The multiple tones are generated by pressing a key.This is the reason for calling the system as Dual Tone Multifrequency. These tones are then decoded by the switching center to determine which key was pressed.
