Dual tone signal decoding and encoding;Remote control device;Signal generator
The keystroke or digital information is converted into a two-tone signal during encoding and transmitted, and the existence of the keystroke or digital information is detected in the received DTMF signal during decoding.
A DTMF signal is made up of audio signals of two frequencies. The frequencies of these two audio signals come from two pre-allocated frequency groups: a row frequency group or a column frequency group. Each pair of such audio signals uniquely represents a number or symbol.
There are usually 16 keys in the telephone, including 10 numeric keys 0-9 and 6 function keys *, #, A, B, C, D. According to the combination principle, there should be 8 different single audio signals. Therefore, there are also 8 kinds of frequencies that can be used, so it is called multi-frequency, and because it uses any one of the high and low frequencies to arbitrarily select the combination for encoding, it is also called "8 out of 2" encoding technology.
According to CCITT's recommendations, the internationally adopted multiple frequencies are 697Hz, 770Hz, 852Hz, 941Hz, 1209Hz, 1336Hz, 1477Hz and 1633Hz. With these 8 frequencies, 16 different combinations can be formed, which represent 16 different numbers or function keys.
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