Abstract: A switch assembly has a back-lit key assembly including an opaque plug, a transparent body lightable from below at least partially to one side of the plug, and a transparent fusing member securing the transparent body and opaque plug together with the fusing member for movement as a unit. A flexible, transparent keypad is secured beneath the key assembly for movement therewith. An electrical contact is secured to the keypad for movement therewith. A board may be disposed at least partially beneath the keypad, the board including a light source disposed at least partially beneath the keypad to illuminate the transparent body and an open electrical circuit adapted to be closed by the electrical contact when the keypad is flexed downwardly.

Abstract: This invention relates to improved trunk interface circuitry for telephone system common equipment, which is used to connect a local customer system to a central office of the telephone company. The improved trunk interface comprises an active two-terminal current sink for limiting the loop current in a non-linear manner, and means for monitoring the voltage across the trunk line which comprises a voltage-to-pulse width converter. The voltage-to-pulse width converter is designed to operate with a microprocessor which measures the time it takes to linearly discharge a capacitor which has been charged to the line voltage.

Abstract: The present invention is embodied in and carried out by a dual channel transmission system with inherent channel identification and extraction. This system employs a data transmission method which has the inherent characteristic that, when two identical receivers are connected to a single signal driver which is transmitting a data stream containing data for each of the channels including one of these receivers, each identical receiver extracts only the data intended for its channel. This method affords the advantage that the signal driver bandwidth may be reassigned by software control so that, when needed, one receiver may extract both channels.

Abstract: A method and apparatus for synchronizing a digital data signal from a first location, such as a digital telephone station, and which is transmitted to a second location, such as the station interface of a telephone switching system common equipment input, with a digital data signal at the second location, is disclosed. The method includes transmitting a data signal to the second location from the first location, receiving the data signal at the second location and determining if the data signal is present at a selected time. Digital coded data is sent to the first location from the second location for selecting successive delay times at the first location. When the delayed data signal is present at the second location at the selected time, the optimum value of the delay time is determined at the second location, preferably by averaging the values of the delay times at which the data signal was first detected and last detected at the second location.

Abstract: A communications system having a common equipment unit and a plurality of telephone station sets coupled to the common equipment unit comprises a common equipment unit having at least one trunk interface for coupling at least one central office telephone line to the common equipment unit and an analog to digital converter for converting analog signals on the telephone line into digital form, and at least one station interface coupling the common equipment unit to at least one of the station sets by a single wire pair.

Abstract: A speakerphone control circuit is disclosed. The control circuit includes a first electronic switch coupled between the speakerphone microphone and a hybrid circuit coupled to the telephone line and a second electronic switch coupled between the speakerphone loudspeaker and the hybrid circuit coupled to the telephone line. A first sensing circuit for sensing the microphone signal and a second sensing circuit for sensing the received loudspeaker signal are provided. The outputs of the first and second sensing circuits are multiplexed and digitized and fed to a microprocessor controller. In response to the levels of the multiplexed signal, the microprocessor determines the state of the speakerphone from among four possible states, including a first talk state, low gain talk state, first listen state and low gain listen state.