Although DTMF works in normal human voice range, the combination of inharmonic frequencies makes it hard for the human voice to impersonate.Īlthough mobile phone networks use digital signals instead of DTMF for direct dialing, DTMF is still used over mobile phones to navigate automated systems such as phone menus, voice menus and other advanced calling services.

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 encoder is either in idle mode (encStatus 0) and is currently not used to encode digits, or it is active (encStatus 1) and generates DTMF tones and pauses of certain duration. The variable encStatus reflects the current status of the encoder. With DTMF, each keypress on your phone generates tones made of two specific frequencies. This DTMF decoder circuit recognizes the phone tone from the phone line and then decodes the pressed key on the keypad of the telephone. DTMF tone generator is controlled by a set of variables. Over the years, DTMF has replaced Pulse dialing, the early type of telephone dialing in which short pulses were used to relay the dialed number. The DTMF keypad is a 4x4 matrix in which each row represents a low frequency and each column represents a high frequency.Pressing a single key sends a sinusoidal tone for each of the two frequencies.

Dual-Tone Multi-Frequency (DTMF) is the signal that you generate when you press an ordinary telephone's touch keys. Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog paths.

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