Abstract: An interactive audio/visual demonstration system for connection to a telephone system, comprising an audio/visual unit connected to an interface circuit. The interface circuit decodes DTMF tones received from the audio/visual unit and in response causes implementation of one or more special features in the telephone system. The interface circuit is preferably connected to an audio track of a video tape recorder, and to the telephone system, such as a PABX, in order to implement a highly interactive video tape presentation in response to a video tape being played on the video tape recorder. The interface circuit is of simple construction and hence durable and inexpensive.

Abstract: This invention relates to a switching system testing arrangement which uses a looparound circuit, into which a test signal is injected and received to determine whether the loop is functioning properly. The system provides means for testing individual switches (or equivalent time division counterpart), individual loops and links between switching stages and the network, complete loops between peripherals, short loops between peripherals and their local control units, or any loop that can be set up within the system, without incurring loss of use of parts of the system which would otherwise be required to obtain the loop but are not of interest to test. The control data and test signals are applied, to set up the loop and into the loop respectively, via message transmission paths which are separate from the loop under test.

Abstract: A circuit for use in conjunction with a microprocessor for refreshing, checking and correcting data signals stored in a dynamic memory. The circuit utilizes a direct memory access controller for transferring data signals stored in successive locations of the dynamic memory to a non-existent peripheral. Data signals appearing on a data bus as a result of the data transfer, are applied to a parity checking circuit for generating an interrupt signal to the microprocessor in response to detection of parity errors in the data signal. The microprocessor then performs a data recovery routine in which correct versions of the data signal stored in a non-volatile memory, are transferred for storage in the dynamic memory under control of a microprocessor. Parity errors in data signals stored in the dynamic memory are thus corrected prior to being accessed by the microprocessor.

Abstract: An electronic telephone handset detector, for generating an output signal to an external controller indicative of a telephone handset being connected to or disconnected from a subscriber's set. A microphone input terminal is connected to a source of direct current such that in the event the microphone is connected to the terminal, direct current flows therethrough. A comparator circuit, connected in a circuit to the microphone input terminal, detects the current flowing through the microphone from the source of direct current and generates the aforementioned output signal in response thereto.

Abstract: A digital progress tone detector, for connection to a telephone line and a PABX, comprising circuitry for generating one or more reference tones having user definable frequencies and performing single frequency discrete Fourier transforms on one or more signals received from the telephone line at the defined frequencies, and providing an output signal to the PABX in response thereto. The output signal provides an indication of whether or not a predetermined one or more progress tone frequencies have been detected in the received signals. Because the generated reference tone frequencies are user definable, the present invention can be easily adapted for use in various foreign countries having different progress tone frequency requirements. A preferred embodiment of the invention is implemented on a single microcomputer chip in conjunction with peripherals (such as codecs, crosspoint switches, etc.).

Abstract: A decimating filter utilizing first and second switched input capacitors for sampling an input signal on opposite phases of a first sampling clock signal. The switched input capacitors are connected to an integrating circuit for filtering the sampling signal. An output of the integrating circuit is sampled according to a second sampling clock signal having a frequency equal to a submultiple of the first sampling clock signal frequency. By sampling the input signal on opposite phases, the input signal is effectively sampled at twice the first sampling clock signal frequency. Accordingly, in applications involving high sampling frequencies, such as digital signal transmission, the input signal can be sampled at a sufficiently high frequency without requiring a prohibitively high input sampling clock frequency. The decimating filter is of simple design and can be inexpensively implemented on an integrated circuit chip requiring small area.

Abstract: This invention relates to a peripheral control unit for a digital switching system. It utilizes a peripheral control network formed of combination time and space division switches which communicate with peripheral cards using a number of time divided lines (channels of which correspond to peripheral units), and communication with the main system central control using a parallel bus connected to a controller and a transceiver, which is connected to the system control via serial time divided lines. In this manner a very few number of wires is required to be connected to the peripheral cards, while allowing selectively simple communication structure and high reliability.

Abstract: A digital switching system which is comprised of a circuit switching network under control of a main system control for carrying and switching transmission paths for signals transmitted between peripherals (i.e. lines, trunks, service circuits, etc.), and a separate message switching network under control of the main system control for carrying supervisory and control signals related to the status of the peripherals between peripheral unit management circuit controller(s) and the main system control.

Abstract: A circuit for transmitting both voice and data at the same time between a subscriber's set and a switching exchange via a bidirectional two wire link. The invention is comprised of a subscriber's set adapted to generate and receive baseband voice signals and data signals, a circuit for 100% amplitude modulating the generated data signal on a carrier signal having its lowest sideband after filtering above the voice signal base band, a circuit for applying the voice signals and modulated carrier to a two-wire subscriber's line, a circuit for separating the voice signals and modulated carrier, and a circuit for demodulating the digital signal and applying the digital signal to control circuits of a switching exchange. Voice signals are applied to voice handling circuits such as the voice switching circuits of the switching machine.

Abstract: A circuit for receiving voice and data signals on a balanced line, the data signal being an amplitude modulated form of a carrier signal having a frequency at least twice as high as the highest frequency in the voice band. The circuit matches the input impedance thereof to a first nominal balanced line impedance with respect to voice signals and a second nominal balanced line impedance with respect to data signals, applies the data signals to an unbalanced data output terminal, and applies the voice signals to a terminal connected to a bidirectional unbalanced input/output lead of a PABX.

Abstract: A method and apparatus is disclosed for automatic control of battery maintenance including fast recharge and equalizing of the voltages on individual cells of the battery. The charging current through a resistance in series with the battery is monitored, and in response, a control circuit energizes a relay which controls the output voltage of a power supply used to charge the battery and drive a load. The control circuit includes a clock, connected to a recharge counter, which effects the recharge process for a predetermined period of time. The recharge counter is connected to the relay which regulates the output voltage of the power supply. The control circuit also includes a battery current sensor, which monitors the charging current of the battery, and a second counter, which provides an enabling signal to the relay for initiating a longer cycle which equalizes the charges on individual cells of the battery if the battery has been recharged from a severely discharge state.

Abstract: An indicator for use with a multiline telephone, which displays the status of both a local and called telephone set. The status indicator is comprised of a first indicator enclosed within a second for displaying by a shade or color the status of a called line, and a second indicator at least partly surrounding the first for partly displaying the first for displaying by shade or color with the second indicator the status of the calling line, whereby a party observing the indicator obtains simultaneous indication of the status of the calling and the called lines. Preferably the first indicator is a circle, enclosed within the second indicator which is a square, both being elements of a liquid crystal display. Each square indicator can be located next to a line access pushbutton with which it is associated.

Abstract: A transformerless, fully balanced, telephone line circuit is provided. Two differential amplifiers are employed, one for incoming signals and the other for outgoing signals. The latter drives the line with two out-of-phase, equal amplitude signals. A comparator detects grounding of either TIP or RING at the telephone to accommodate international applications.

Abstract: An apparatus and method of controlling the loop gain in a loudspeaking telephone comprising storing reduced representations of an outgoing signal and an incoming signal in corresponding incoming and outgoing storage circuits respectively, in which the storage circuits have much faster attack times than decay times, comparing the representations, and controlling the gains of outgoing and incoming signal paths of the loop according to the degree and polarity of the result of the comparison. With the outgoing signal path connected to a microphone or a signal source and the incoming signal path connected to a loudspeaker, hands-free communication can be carried on having much more natural characteristics than in the past, devoid of most of the "hollow" sound characteristic of prior art systems.

Abstract: A planarizing process for producing a passivation or insulating layer immediately underlying an upper metallized layer on the surface of an integrated circuit having very large radius of curvature steps, thus providing a reliable base for the metallized layer. The process is comprised of the steps of depositing and defining first metal conductors on the surface of an integrated circuit, depositing a first dielectric layer over the surface of the integrated circuit including the conductors, the dielectric layer being comprised of material selected from the group comprised of silicon dioxide and silicon nitride, depositing and polymerizing a layer of negative isoprene resist over the surface of the dielectric layer, plasma etching the surface of the isoprene and dielectric layers to a predetermined thickness over the metal conductors in an atmosphere of CF.sub.

Abstract: A lock for retaining a printed circuit board within a frame, which can be used adjacent opposite front covers of the front edge of the printed circuit board to increase the structural rigidity of the frame when locked. This allows the printed circuit boards to be shipped within the frame direct from the factory within an entire fully tested system, with reliability, avoiding damage which often previously occurred due to vibrations and bouncing during transportation. Each lock is comprised of a lever, a protrusion for rotatably attaching the lever to the printed circuit board at a fulcrum point spaced from the axis of the lever, and a latch fixed to the lever at a position closer to the lever and closer to one end of the lever than the fulcrum point, whereby the latch can be rotated over-center relative to the fulcrum point into a cooperating hook and locked therein as the lever is rotated about the fulcrum point.