Key telephone intercom line system

Details Key telephone intercom line system Key telephone intercom line system

1976-09-21

1978-03-28

Claffy, Kathleen H.

179 18AD, 179 18BF, H04M 172

Patent

active

040816249

ABSTRACT:
The disclosure relates to a key telephone system intercom line circuit which uses only three leads to connect plural telephones and an intercom line control circuit. These leads comprise two talking circuit leads and one control lead. Exclusion circuits in each of the telephones are controlled by signals applied on the single control lead (1) to allow a telephone to seize the intercom line circuit when it is in an idle state, (2) to allow a called telephone (signalled via a separate pair of calling leads) to answer without being excluded and (3) to exclude all other telephones from the intercom line circuit after the calling telephone has seized the intercom line circuit. Indicators in each telephone associated with particular intercom line circuits provide a visual signal at each telephone set concerning the status of the intercom line circuit by (1) not being lit when the intercom line circuit is in an idle state (2) flashing periodically when the intercom line circuit is in the seized state and (3) being continuously lit when the intercom line is in a talking state.

REFERENCES:
patent: 3860763 (1975-01-01), Sudoh et al.
patent: 3872261 (1975-03-01), Shinoi et al.
patent: 3904834 (1975-09-01), Shinoi et al.
patent: 3961144 (1976-06-01), Hirate

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