DTMF Communication system

摘要

A highly flexible and economical dual tone multiple frequency (DTMF) communication system includes a data input source such as a keyboard; a repertory dialer or electronic memory; an integratable digital encoder which includes a digital sine wave synthesizer; and a transmission unit such as a radio or a connection to a standard utility telephone system. The digital encoder provides a DTMF output signal at standard telephone frequencies in response to input data and includes a predial delay circuit which allows for dial tone delay or transmitter start up after receipt of data and before generation of an output signal, a two second delay circuit providing a two second output signal which may be utilized to prevent shut down between successive number entries and to lock out noise from a microphone or to a speaker and an automatic number insertion (ANI) circuit. When enabled, the automatic number insertion circuit automatically locks out a keyboard or other data source and transmits a 4 or 8 digit number supplied by a ROM before transmitting keyboard information. The ANI number may be used for automatic dialing, as a station identifier preceeding radio transmissions or as a code key enabling access to restricted information. Additional features provide in even further operator convenience.