Telephone-call prohibit circuit
US4482787A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 4, 1983 |
| Grant date | Nov 13, 1984 |
| Priority date | — |
| Expiry date | Jan 4, 2003 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/677
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A circuit for preventing a telephone set from being used without approval, the telephone set including a handset, telephone lines coupled to the handset, a dial pulse signal generator and hookswitches for coupling the telephone lines to the handset and for cooperating with the handset. A circuit is provided for converting the dial pulse signals into a binary code, a prohibit circuit is provided for generating a prohibit signal which prohibits a telephone call when the binary codes corresponding to prohibited dial numbers are input thereto, and an unlock circuit is provided for generating during a predetermined period a control signal which allows a telephone call when the binary codes corresponding to secret dial numbers are input thereto. A transfer switching means is provided for selectively coupling the converting circuit to either the prohibit circuit or to the unlock circuit and for cooperating with the hookswitches. A gate circuit is provided for preventing the passing of the prohibit signal of the prohibit circuit in response to the control signal of the unlock circuit, and a switch is provided for breaking the telephone lines in response to the prohibit signal from the gate…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.