Key telephone privacy circuit
US4117274A · kind A · utility
8Cited by
5References
4Claims
0Family size
Assignee
Inventors
Key dates
| Filing date | Dec 26, 1973 |
| Grant date | Sep 26, 1978 |
| Priority date | — |
| Expiry date | Dec 26, 1993 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M1/68
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A privacy circuit for use in a key telephone station set is disclosed. Using only a single relay, the privacy circuit operates to exclude the user from a busy central office line while allowing the user to gain access to an idle line. The privacy circuit is positive acting and cannot be circumvented by manipulating the keys and/or switchhook while at the same time allowing service to continue during a local power failure. Additional circuitry is provided to allow conference connections among key telephone sets equipped with privacy circuits.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.