Patent
1979-04-16
1981-02-24
Cardillo, Jr., Raymond F.
H04M 1104
Patent
active
042529972
ABSTRACT:
A ring-down or non-dial subscriber telephone such as a freeway emergency telephone is connected to automatic electronic switching (EAX) equipment for interconnection with an emergency operator by an interface circuit having a polarity-sensitive full-wave bridge controlling voice connection of the telephone to the operator. Actuation of the bridge is controlled by a current sensitive controller connected in series with the originating loop containing the freeway telephone. The bridge monitors the on-hook and off-hook states of the called telephone and energizes alarm circuitry upon failure of the calling telephone to go on-hook within a predetermined time after the called telephone goes on-hook. The circuit also has a capability of monitoring current flow in the originating loop containing the calling telephone and of energizing a common alarm circuit in the EAX equipment in the absence of such current flow. Circuit elements are also provided for disconnecting the interface circuit from the common alarm system while retaining identification of the calling telephone responsible for the alarm condition.
REFERENCES:
patent: 3748389 (1973-07-01), Casterline et al.
Lodas Gregory W.
Stewart Dennis M.
Cardillo, Jr. Raymond F.
General Telephone Company of California
Lawler John F.
Popek Joseph A.
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