Abstract: In an attachment apparatus for a key telephone system of the type which permits a plurality of intercom substations to access a trunk telephone line via a common communication circuit, a novel subset operable switching circuit is disclosed that permits each subset access to said common communication circuit only on an individual one-at-a-time basis. Transistor circuitry is provided to lock out other stations when more than one subset tries to gain access at the same time.

Abstract: An attachment to key telephone system apparatus is disclosed which permits an intercom substation to access a trunk telephone line. This includes an intercom-to-trunk line access unit for coupling telephonic communications between its input and a selected one of a plurality of trunk lines connected to its output. The unit contains a selector, an advancing means and means responsive to at least one dial digit selection type signal at an input for advancing the selector to a trunk line directly or by means of a nonbusy trunk hunting mode of operation. Relay means are provided at a key service unit, responsive to operation of push button switch means at the selected intercom substation, for interrupting the communications circuits between the intercom substation and the intercom circuit in the key service unit and establishing the communication circuits between the intercom substation and the input of the intercom-to-trunk access unit.

Abstract: An attachment to key telephone system apparatus is disclosed which permits an intercom substation to access a trunk telephone line. This includes an intercom-to-trunk line access unit for coupling telephonic communications between its input and a selected one of a plurality of trunk lines connected to its output. The unit contains a selector, an advancing means and means responsive to at least one dial digit selection type signal at an input for advancing the selector to a trunk line directly or by means of a nonbusy trunk hunting mode of operation. Relay means are provided at a key service unit, responsive to operation of push button switch means at the selected intercom substation, for interrupting the communications circuits between the intercom substation and the intercom circuit in the key service unit and establishing the communication circuits between the intercom substation and the input of the intercom-to-trunk access unit.

Abstract: Means and methods are disclosed to prevent dialing of long distance telephone calls from a restricted local substation by counting the number of digits dialed at that station and preventing the sending of further digits once the count attains a predetermined number. Means are also included by which the initial dialing of the digit zero, which might enable one to obtain access to the long distance telephone operator, also results in disabling of the telephone dial.

Abstract: Improved means are disclosed to prevent a restricted local telephone substation or set from dialing long distance telephone calls by counting the number of digits dialed at the station and preventing the sending of additional digits once the count attains a predetermined number. An electronic counter and a Nand gate latch circuit are arranged in a novel manner in which responsive to the local station going off-hook the Nand gate latch is set into a second condition and the counter is enabled to receive and count pulses from the substation. Means coupled to an output of the counter reset the Nand gate latch to its first condition should the count exceed the predetermined number. Additional means are included in combination by which the dialing of the digit zero as the first digit of a called number also results in resetting the latch.

Abstract: A touch type dial digit selector to rotary type dial digit sender converts touch type dial input information to a rotary type dial output and includes a touch type selector pad having the ten digit selecting push buttons arranged in four rows and three columns and associated row and column switches, an encoder for converting the information represented by the operation of the row and column switches into a four-bit binary code, a storage and pulsing circuit for receiving the digit information, and providing at an output the series of pulses representative of the dialed number. The storage and pulsing circuit includes a strobe input for initiating the registration of the input information by the storage and pulsing circuit. Means responsive to the concurrent operation of at least one row switch and at least one column switch of said touch type selector provide a strobe pulse to said strobe input at the end of a predetermined time interval greater than N seconds.

Abstract: An electronic selector switch is disclosed that enables selection of one of a plurality of output circuits.