Two-wire intercom with hands-free function

Details Two-wire intercom with hands-free function Two-wire intercom with hands-free function

1992-03-27

1993-07-13

Schreyer, Stafford

Telephonic communications

Private or single line system

Lockout

379172, 379169, H04M 904, H04M 908, H04M 1100

Patent

active

052280780

ABSTRACT:
An intercom system for a door and inside stations has a speech function for two-way communication with hands-free operation. The intercom system includes a two-wire connecting lead between the door station and each inside station to transmit a conversation current and an operating current. The intercom system includes a bridge circuit for suppressing feedback, a bipole circuit to decouple conversation currents from a power supply, a calling circuit for calling on the two-wire connecting lead and using a call current of opposite plurality with respect to the operating current, and a short-circuit circuit in each inside station for short-circuiting the corresponding two-wire connecting lead when the corresponding door opening button is actuated.

REFERENCES:
patent: 3743791 (1973-07-01), Duff et al.
patent: 3761630 (1973-09-01), Silitch

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