Tone dial toll restrictor
US4177358A · kind A · utility
Inventor
Key dates
| Filing date | Jun 21, 1978 |
| Grant date | Dec 4, 1979 |
| Priority date | — |
| Expiry date | Jun 21, 1998 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/677
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
Logic circuits including electronic switching are provided for admitting or rejecting signals from a dual multi-frequency telephone into a trunk line, or toll line, the initiating control of which is provided from a dial tone signal feeding a detection circuit whereby selective recognition of coded signals permits further processing into the trunk line, there being additional, specific logic circuits for preventing further processing of the coded signals when a "zero" or a "one" numerical digit is recognized as the first signal. If the dial tone signal is not detected, the telephone line connected to a telephone is held at a voltage polarity which prevents dialed signals from the telephone from reaching the telephone line. When a dial tone is detected, the line polarity is reversed, thereby permitting dialed signals to reach the line.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.