Abstract: A device is provided for connection to a shared telephone line for detecting and audibly indicating the on-hook and off-hook status of the line. The device includes sensing and changing circuitry connected to the shared telephone line for detecting a voltage step occurring during status change transitions between on-hook and off-hook states and correspondingly changing the device during these status changes transitions so that the device is prohibited from drawing power from the shared telephone line when the shared telephone line in not in use. A piezo speaker produces audible on-hook and off-hook sights corresponding to on-hook and off-hook states of the telephone line.

Abstract: A multi-link communication system includes a number of stations and interconnecting audio links under the control of a central computer. Each station is addressable by the computer for connecting selected stations to a selected audio link for establishing audio communication between stations. Each station has at least one corresponding access circuit for establishing an audio connection to a selected or preassigned link, and the connection is maintained by a corresponding memory circuit that is addressable by the computer. A group of output lines from the computer are used as select inputs to an analog multiplexer connecting a bidirectional control line to the selected access circuit for connecting or disconnecting the corresponding station and also for receiving connect or disconnect requests from the corresponding station. In a particular embodiment, the stations include multi-link dial and dialless telephones, single-link dialless telephones, and intercom speakers in an automatic private branch exchange.

Abstract: A user programmable clock which is both simple to program and capable of executing relatively complex events. The front panel has a display divided into a plurality of functional blocks, with an operator positionable pointer adapted to activate any block. A single keypad is used to enter data in the respective blocks designated by the pointer. The system allows programming of comparatively complex events, capable of relating a single time to any combination of days and any combination of zones. Event programming is further simplified by providing an immediate indication of an erroneous entry along with a signal distinguishing between various potential types of errors.

Abstract: An administrative telephone system for use in schools, hospitals and the like which includes a dialable administrative telephone set and a plurality of dialless remote or "staff" telephone stations having identifying numbers, interconnected by a central exchange. The administrator can dial any staff telephone station by pressing two digit buttons on the dial pad. Associated with the administrative telephone set is a digital display device having a column of display positions. Each staff telephone station has a call-in switch. The central exchange includes storage provision coupled to the digital display for registering and displaying, in order, the numbers of the staff telephone sets which have called in and thus have indicated a desire to communicate with the administrator.