Abstract: The invention relates to methods for testing analog telephone line equipment including, in particular to detect faults in their hybrid resistor arrays. It consists in isolating the equipment from the telephone line and then applying the normal ringing signal to it. If the resistor array is defective, the output logic signal of the off-hook/on-hook detector circuit comprises a succession of 0 and 1 at the frequency of the ringing signal, which indicates the fault. This makes it possible to eliminate the equipment test relay usually employed.

Abstract: An apparatus for controlling operation of a recording device with a telephone configured for orientation in a first state and a second state includes: (a) an information conveying section for conveying information from the telephone to a recording locus in the recording device; (b) an indicating section for receiving a monitor signal having a first value when the telephone is in the first state and having a second value when the telephone is in the second state; the indicating section employs a single fixed bias to generate a first indicating signal when the telephone is in the first state and to generate a second indicating signal when the telephone is in the second state; and (c) an engaging section; the engaging section responds to the first and second indicating signals to orient the recording device for recording the information or for not recording.

Abstract: A communication peripheral apparatus automatic line searcher includes a CPU (central processing unit) connected to two ring detectors, two hold detectors, two in-use detectors and a loop detector, the ring detectors, hold detectors and in-use detectors being respectively connected to a first telephone line and a second telephone line, the first telephone line and the second telephone line being respectively connected to contacts of a first relay, the first relay having a center contact connected to the normal-close contact of a second relay. The CPU automatically switches the vacant telephone to the vacant telephone line upon a call through one telephone line. The relays are switched to drive the phone power through the CPU to indicate the in-use status of the corresponding telephone line.

Abstract: A communications detector for detecting remote user hang-up or disconnection by a telephone answering machine (TAM). The remote hang-up detector (RHUD) may operate in conjunction with a modem and does not affect transmission and receipt of modem signals and modem performance. An optically isolated voltage detector indicates to the TAM that the remote user has hung up by detecting reversal or interruption of the loop current supplied by the central office, thereby causing the local user or modem to likewise hang up.

Abstract: A ring generator circuit is included in a subscriber line interface circuit (SLIC) for providing a high voltage ring signal to a plurality of ringers at the same time. The ring generator circuit includes an adder and divider circuit connected to receive a DC offset and an AC reference signal from the SLIC. The adder and divider circuit outputs a fractionalized summed signal. That signal is supplied to a full-wave rectifier, which rectifies the fractionalized summed signal so that it is always a positive voltage. The rectified signal is supplied to a switch control circuit, a first amplifier and a second amplifier. The first and second amplifiers have the same gain, but with opposite signs or polarities. The outputs of the first and second amplifiers are sent to a commutating switch, which is controlled by an output of the switch control circuit.

Abstract: A subscriber line circuit for a telephone network having current controlled switches and current sources. Methods of making and using the components are also disclosed.

Abstract: A circuit and method for reducing power consumption during operation of a solid state switch that controls connection of a source of alternating current to a load includes a circuit for determining a voltage across the switch. The switch is operated upon receipt of both a command signal and an indication that the voltage across the switch is less than a predetermined value. When used in a telephone system subscriber line interface circuit (SLIC), the circuit controls two switches that connect an ac ring signal from an ring generator to a telephone. The voltage sensed across the switch may be converted to a low current level and the circuit embodied in an integrated circuit.

Abstract: DC level control for an electronic telephone line card which filters the DC component from the input audio signal, determines the gain setting of the transmit path, develops a DC adjust voltage opposite to that of the DC shift component and subtracts the DC adjust voltage to the input voltage to cancel the DC shift component. A quantized, discontinuous feedback path is implemented to respond only to DC shifts so the AC operation remains substantially unaffected. Such discontinuous feedback eliminates stability and impedance matching problems introduced with continuous feedback solutions. A DC control circuit according to the present invention includes a low pass filter for detecting DC shifts, a quantizer for asserting an incremental signal, a threshold detector for activating adjustment functions, and an accumulator for developing the DC adjust voltage by incremental steps.

Abstract: A subscriber line control device utilizes a scan input table and a last look table. The scan input table stores respective current line states of a plurality of analog subscriber lines. The last look table stores respective preceding line states of the plurality of analog subscriber lines and information for validating or invalidating a timer device. A valid timer device corresponds to when a monitoring process is required. The scan input table is compared with the last look table at every predetermined cycle. When they do not match, it is judged whether the line state has changed or if the timer device is validated. Based on the judging result, an analog subscriber line control is performed according to an instruction specified by a call processing unit. The analog subscriber control is any of a call origination monitor, a dial pulse monitor, and an on-hook and off-hook (HIT) monitor.

Abstract: A subscriber circuit comprising a monitor circuit operating with a power supply voltage supplied to a subscriber instrument and monitoring an operation of the subscriber instrument for generating a monitor signal indicative of the result of monitor, and a power supply voltage abnormality detecting circuit receiving the power supply voltage supplied to the subscriber instrument, for generating an active abnormality detection signal when the power supply voltage deviates from a predetermined voltage range.

Abstract: A telephone line interface circuit with d.c. amplifiers coupled to tip and ring paths is protected against transient voltages by a crowbar-type protection device coupled via a diode bridge to the tip and ring paths, positive and negative terminals of the diode bridge being connected respectively to ground and via a diode to a negative supply voltage line for the amplifiers. The diode prevents discharge of a capacitor, coupled between the negative supply voltage line and ground, through the protection device when it conducts. A locked up state, in which the amplifiers maintain holding current to the protection device after a transient voltage, is avoided by further diodes coupled from the negative terminal of the diode bridge to inputs of the amplifters, or by controlling a current limiter to interrupt current to the capacitor when the diode is reverse biased, so that the capacitor discharges.

Abstract: A detector circuit is provided for detecting the off-hook status of the extension telephone line. The detector is connected to tip and ring lines of the telephone line for determining a change in the voltage between the tip and ring lines. The detector includes a low pass filter for filtering noise and AC signals. The filtered signals are transmitted through a converter which converts a differential voltage between the signals into an absolute voltage relative to a ground. A pair of voltage peak detectors generate output signals in response to changes in the absolute voltage. A first peak detector provides a quickly varying output signal representing an instantaneous voltage. The second peak detector provides a slowly varying output response representative of an average voltage over a period of time. The average voltage is employed as a reference voltage against which the instantaneous voltage is compared.

Abstract: Apparatus for detecting whether a telephone call has been disconnected, which apparatus includes: (a) a click detector for detecting a click and for generating a "click indication"; (b) a telephone handset impact detector for detecting a telephone handset impact and for generating a "handset impact indication"; (c) a silence detector for detecting silence and for storing a "silent indication"; (d) a timer for determining a predetermined time interval and for transmitting a signal to a controller whenever the time period expires; wherein, in response to the signal, the controller analyzes the "click indication", the handset impact indication", and the "silent indication" to determine whether a predetermined sequence of handset impact, clicks, and silence was detected and, if so, for generating a signal indicating that the telephone call has been disconnected.

Abstract: In a telephone answering machine, a detector for a automatic disconnect function uses a first amplifier to detect, amplify, and invert small input signal changes, and second amplifier to detect large input signal changes and a logic arrangement responsive to the output signals of the first and second amplifiers to detect the presence of only the small input signal changes.

Abstract: A telephone line card circuit includes an operational amplifier circuit having first and second inputs and an output. A field-effect transistor circuit has first, second and control electrodes, the control electrode is coupled to the output of the operational amplifier circuit, the first electrode is coupled to the TIP/RING terminal, and the second electrode is coupled to the second input of the operational amplifier circuit. A first resistor is coupled between the TIP/RING terminal and the first input of the operational amplifier circuit. A second resistor is coupled between the first input of the operational amplifier circuit and a terminal of the circuit whereby the terminal of the circuit is typically coupled to a supply voltage terminal.

Abstract: An information separation device having a transformer operating as a separating filter to separate transmitted direct current power and alternating voltage information. The transformer has at least two windings on a first side holding power in reserve. Between these windings a capacitor is serially coupled that transmits information signals. The windings are coupled at their other ends to transmission lines for direct current power and alternating voltage information. The transformer has another winding on the second side that processes received information. Two controllable inverse valves are coupled by their output electrodes between the transmission lines. The control electrodes of the valves are coupled to a load-independent voltage source during a transmission signal.

Abstract: Apparatus in an automatic telecommunications system which communicates between a central location and at least one remote location over the switched telephone network, senses changes in loading of the telephone line which correspond to a telephone going off-hook, to serve as an indication that a telephone has gone off-hook and to cause the automatic telecommunications system to relinquish its use of the telephone line, or not to go off-hook if a telephone is in use.

Abstract: A loop closure detector for a two-wire telephone line comprises a four-arm resistive bridge, in which the four arms are constituted respectively by a first battery feed resistor, the two-wire line in series with a second battery feed resistor, and two resistors forming a potential divider across the battery voltage which is coupled across one diagonal of the bridge. A voltage sensing circuit, constituted by a comparator or a light emitting diode, is connected across the other diagonal of the bridge to provide an output representing a loop closure state of the line. A ring-ground detector is also described using a similar bridge and voltage sensing arrangements.

Abstract: A transformerless hybrid circuit arrangement for a subscriber line interface circuit of a telecommunications exchange is disclosed. A preferred embodiment of the hybrid arrangement comprises a first and a second operational amplifier plus a differential amplifier connected together in the following manner: The non-inverting input of the first operational amplifier is connected to a first reference voltage and the output of this amplifier is connected (1) via a first resistor to one wire of the two-wire subscriber line, and (2) via a third resistor to the inverting input of the amplifier. The non-inverting input of the second operational amplifier is connected to a second reference voltage and to the receiving branch of the four-wire line of the telecommunications exchange.

Abstract: A subscriber line interface circuit receives and twice inverts currents from a 2-wire subscriber line and returns the currents to the subscriber line so longitudinal input impedance is low. Any differential input current in the subscriber lines is bypassed by a capacitor, so differential input impedance is very high. The circuit also sends a signal current from one system having one ground to another system having a different ground through one current path, while sending another current, having a phase opposite and amplitude equal to the signal current, through another path. This effectively isolates the two systems having different grounds.

Abstract: A subscriber line interface circuit comprises a balanced amplifier having positive and negative inputs for amplifying a voltage thereacross to generate a pair of mutually complementary voltages across true and complementary outputs. Four resistors of a first value are respectively connected between a subscriber tip line and the negative input, between a subscriber ring line and the positive input, between the negative input and true output and between the positive input and complementary output. Two resistors of a second value smaller than the impedance of the subscriber loop are respectively connected between the tip line and the complementary output and between the ring line and the true output. A DC feedback circuit is connected to the complementary output to generate a DC feedback signal according to a desired variable DC power feeding characteristic.

Abstract: The invention relates to circuitry for providing and monitoring the status of telephones, especially those used in conjunction with advanced telephone answering machines, such as is also disclosed herein. The voltage on the extension line leading to the telephone set (termination device) is monitored to determine whether the telephone set is on-hook or off-hook. Also, a tone decoder monitors DTMF signals on the extension line. The telephone set, when off-hook, is normally connected to the subscriber line. However, if a predetermined digit is keyed into the telephone set, the telephone set will be disconnected from the subscriber telephone line and connected to a selectively actuable current source. The telephone set, being powered by the current source and being disconnected from the subscriber line, can then be used for the control and monitoring of the telephone answering machine. Also, the current source is protected against the application of the subscriber line voltage.

Abstract: A communication system having remotely controllable signal receiving means for automatically setting the receive function for a start-signal transmitted from a terminal device and for changing the receive function when the terminal device is changed. At start-up, a main processor reads start-signal type information for each of the terminal devices from a main memory. The line circuits associated with the respective terminal devices are then set with a start-signal receive function according to the start-signal type information. When a terminal device is added or changed, the start-signal receive function is changed by merely updating the start-signal type information stored in the main memory.

Abstract: A telephone circuit for ring trip detection that can be monolithically integrated, includes a current transducer coupled to a user's telephone line, and an integrator circuit. The output current of the current transducer is proportional to the line current until equal and opposite threshold values are reached. When the line current threshold values are exceeded, the transducer output current is constant. The transducer output current is integrated by the integrator circuit over at least one complete cycle. When a telephone headset is removed, a direct current is applied to the ringing signal current resulting in asymmetry in the half-cycles of the transducer output current. The asymmetry provides a non-zero integrated current for a complete cycle. When the integrated value of the asymmetrical current is greater than a selected value, a signal is applied to the ringing circuit, halting the ringing signal.

Abstract: A circuit providing a message waiting indication using a light emitting diode and a constant current surge protected circuit for use with PABX extension telephone instruments. Recently developed light emitting diodes operated with current of one milliampere or less are effectively used in the present circuitry which limits current to the device in the operating mode and also as low leakage current while in the "off" mode.