DTMF Communication system
US4087638A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 1, 1976 |
| Grant date | May 2, 1978 |
| Priority date | — |
| Expiry date | Oct 1, 1996 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/30
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
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 en…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.