Abstract: Transient signal elimination circuitry is disposed in a local communications loop extending from a subscriber telephone to a telephone central office couples ringing and on-hook and off-hook signals through the loop after removing transients in these signals. The circuitry also isolates the telephone subscriber and central office from the local loop until an off-hook signal is detected and restores this isolation when an on-hook condition exists at the telephone subscriber. Transient signal elimination is accomplished with a CPU driven interface which detects undesirable transients such as a ringing or off-hook signal, and in response thereto generates a burst of double tone signal to alert connected equipment. In this manner, the local loop can be simultaneously used for both voice communications and a second information signal with each signal capable of occupying the same bandwidth. These signals can operate independently of each other.

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 private branch exchange for use with different types of telephone sets comprises a current detection device such as a photo-coupler for detecting a current flowing through a data line connecting to a multifunction telephone set to discriminate among different types of telephone sets and a current limiting circuit for limiting a current supplied from a power source device through a voice line in accordance with an detected output from said current detection device.

Abstract: Apparatus and method for receiving and decoding the bursts of line current activity produced by rotary dial action in dialing a sequence of digits. In accordance with the apparatus of the present invention, a rotary dial pulse receiver counts the number of bursts of line current activity produced by a given telephone handset in dialing a standard test digit. A conversion means selects a conversion algorithm which is effective to express the relationship between the number of bursts counted and the value of the digit dialed and applies the selected algorithm to decode the value of subsequent non-standard digits dialed. In accordance with the method of the present invention, a method of converting the number of bursts in line current activity produced through rotary dial action in dialing a sequence of digits by selecting and applying a conversion algorithm is described.

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: The hangup apparatus uses an inadvertent off-hook detector circuit designed to detect the off-hook "howler" alert signal transmitted to a telephone by the telephone company when the telephone has been off-hook for a period of time without any user activity. The detector circuit provides an automatic hangup signal to an automatically actuated hangup switch, disconnecting the telephone voice network from the telephone lines and restoring service to the telephone. One version of the invention can be incorporated into newly manufactured telephones, and another is suitable for use with existing telephones. Both versions can be realized using readily available commercial electronic components.

Abstract: A circuit for implementing a connection of an operational amplifier, and for achieving the switchable sensitivity of the same, as well as the in-and-out switchable filter elements, which results in a low cost, universally applicable line circuit interconnect circuit.

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: Transient signal elimination circuitry is disposed in a local communications loop extending from a subscriber telephone to a telephone central office couples ringing and on-hook and off-hook signals through the loop after removing transients in these signals. The circuitry also isolates the telephone subscriber and central office from the local loop until and off-hook signal is detected and restores this isolation when an on-hook condition exits at the telephone subscriber. In this manner, the local loop can be simultaneously used for both voice communications and a second information signal with each signal capable of occupying the same bandwidth. These signals can operate independently of each other.

Abstract: A pulse detector system for reliably counting pulse signals generated by calling party telephone dials. The system includes generating a dial pulse template based on a sample train of pulses. A preferred embodiment uses a pulse amplitude template comprising an amplitude histogram.

Abstract: A solid-state telephone trunk interface circuit provides high isolation between a central office and telephone equipment. Opto-isolator transistors and a transformer are used to isolate the central office and the local equipment portions of the circuit. A switching transistor (Q4) is connected between a ring connector (3) and turned on and off via an opto-isolator transistor connected to a control connector (9). A ring detector (11) comprising a first diode bridge is connected between tip and ring connectors (2 and 3) via an opto-isolator transistor to a ring signal connector (13). First and second parallel and opposite sign line condition detectors are respectively connected between tip and ring connectors and via opto-isolator transistors to battery-reverse and battery-forward signal connectors (19 and 17). The voice circuit includes a second diode bridge connecting tip and ring connectors to a first winding of a transformer (T1).

Abstract: A communication terminal apparatus having a handset which includes a transmitter, a receiver and a hook switch. The handset is connected to the main body through a modular jack having four pins. The handset includes a bypass circuit for flowing a d.c. component therethrough by bypassing the transmitter or receiver and a capacitor, which is connected in parallel with the bypass circuit and in series with the transmitter or receiver, for cutting a d.c. component. Thus, the status information of the hook switch is applied to a signal line of the transmitter or receiver in a d.c. format superimposingly.

Abstract: The invention provides a tip party identification facility in association with a subscriber line interface circuit. The tip party identification facility takes advantage of a shutdown feature and the output of a common mode error amplifier of the subscriber line interface circuit. The use of this facility enables the central office to determine whether the tip party or ring party is off-hook for billing purposes.

Abstract: A telephone circuit, which may be monolithically integrated, for supplying ringing signals to a subscriber's telephone line and for detecting an off the hook condition during ringing, including a logic control circuit connected to exchange components which control the supply of the ringing signals and determine their rhythm. The logic control circuit is connected to a circuit for detecting direct current on the line and a current comparator for generating a signal when the value of the line current exceeds a predetermined current value. This signal is also supplied to the exchange components via a transfer circuit to inform them that an off the hook condition has taken place. The logic control circuit is connected to a timing signal generator which synchronizes its functions with times in which the ringing signal has a zero amplitude, and is connected to a signal amplifier circuit which supplies the ringing signals to the line and to the transfer circuit.

Abstract: A method is disclosed for measuring telephone dial pulse parameters independent of telephone subscriber line length. To avoid distortions resulting from varying subscriber line lengths, there is performed during the first pulse interval of a dial pulse series to be measured, a voltage measurement with results in a value that depends on the line length, and, in accordance with this value, the times measured for pulse interval and pulse duration of the dial pulse series are corrected.

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: An apparatus for effectively monitoring the hook status of a remotely stationed telephone, and a sub-audible tone associated with a corresponding alarm reporting device, monitors variations in impedance in the subscriber loop, preferably from the central facility which is monitoring the remote location. To this end, a disturbance (voltaage signal) is introduced onto the subscriber loop by an appropriate source. Steps are then taken to measure potential variations in this voltage signal, and to determine the hook status of the subscriber loop based upon these variations in potential. To make sure that the ancillary equipment which is being connected to the telephone network will not adversely affect basic telephone services, care is taken to make sure that the signal which is introduced onto the subscriber loop will neither create audible noises on the telephone line, nor interfere with the operation of the switching equipment of the telephone company.

Abstract: A parallel off hook detector for an electronic remote data recorder includes a short-integrator and a long-term integrator, both monitoring the voltage on a line. The integrated outputs of the short-term and long-term integrators are compared to determine whether the outputs maintain a predetermined difference for a predetermined minimum time characteristic of an impedance being connected across or removed from the line.

Abstract: A device for detecting a specified signal on a conventional telephone line includes a pair of input terminals to which to connect a pair of conventional telephone lines, and a circuit connected to the input terminals that draws a different amount of power from a separate power source when the specified signal is present across the input terminals thant it draws otherwise. A transformer couples the power supply to the circuit while isolating the power source from the input terminals, and power sensing circuitry that senses a difference in power supplied to the transformer generates a control signal that is also isolated from the input terminals.

Abstract: A key telephone system for use with at least two telephone lines that extend between a central office and two or more telephone stations. Each station is capable of responding to a manually-actuated hold select switch by establishing a hold condition on one of the lines and by connecting a line terminating impedance across the line that is to be held. Each station is further capable of monitoring the state of each line, and indicating the state of each line, without applying any indicating signals to the telephone lines. Each station furthermore determines threshold voltages for on-hook, off-hook and hold line states and determines line state by comparison of line voltage with such threshold voltages.

Abstract: Detector circuitry monitors the line voltage on a telephone line to detect an off-hook condition. In order to accomodate varying line voltages and noise conditions, the circuitry automatically selects a threshold off-hook voltage by an iterative initialization procedure which is initiated on circuit power-up. The intialization procedure repeatedly compares the threshold voltage to the actual line voltage over a period of time to eliminate false off-hook detection due to noise.

Abstract: A driver circuit to drive an M-lead in a tie trunk between telephone branch exchanges is disclosed. The driver continues to provide for a current increase as the resistance of the load on the M-lead decreases, until at a particular point maximum current is achieved. After this point, as the resistance of the load continues to decrease, the driver circuit decreases the load current, such that power dissipation in the driver is kept at a safe level for a device. The V-I characteristic of the driver circuit is such that for any given value of load resistance, the circuit has only one possible point of operation which will eliminate any possibility of latch-up. Simplicity and precision are also achieved by this circuit. The accuracy of the performance characteristic is limited only by the tolerance of the passive components used.

Abstract: An improvement to automatic answering and call forwarding features used in telephone communications which allows a user to remotely activate, modify, and deactivate these features. The improvement describes a transformerless means for coupling signals to and from the telephone line without compromising the operation of the telephone line. The apparatus employs a microprocessor controller (11) with memory (12), a tone encoder (15), a toner decoder (14), a voice synthesizer (16), a timer (13), a cassette interface (17), an RS232C interface (20), a switching matrix (21), and a line interface (22). Audio, pulse dial, and tone signals are routed among the components and the telephone line (51) by the switching matrix (21) and line interface (22). The line interface (22) provides a transformerless means for coupling signals to and from the telephone line (51) and also analyzes the status of, and signals present on, the telephone line (51).

Abstract: A communication system is connected to a pair of telephone conductors which supply telephone service to a telephone subscriber. An optically coupled switch connects a first winding of a transformer across the telephone conductors. A second winding of the transformer is connected to a modem for communicating over the telephone conductors via the transformer. A voltage sensor circuit senses the voltage across the telephone conductors and detects a reduction in the voltage level across the conductors which indicates an off-hook condition of a telephone unit of the subscriber connected to the conductors. The voltage sensor circuit also detects the presence of a ring signal on the conductors. The switch is periodically opened so as to disconnect the transformer from the telephone conductors, and permit the voltage sensor circuit to check for an off-hook condition.

Abstract: The flow of direct current and/or ringing alternating current in a telephone line subscriber loop is detected by means of current flow detectors. The output signals produced by the current flow detectors are applied to an evaluation circuit, the zero-crossings of the ringing alternating current being used to determine whether a ringing alternating current has been superimposed on the loop direct current.In order to increase the reliability of the evaluation and to detect noise voltages coupled into the subscriber-loop, the durations of positive and negative half-waves of the loop current are measured and the evaluation is effected by comparing the sum and the ratios of the measured values relative to a presettable threshold.

Abstract: A circuit for detecting a first plurality of status signals on a multiplicity of telephone lines and generating a second lesser plurality of control signals, less than the first plurality, in response thereto. Predetermined ones of the control signals are transmitted via a multiplexing circuit to a comparator circuit. A digital-to-analog converter generates analog threshold voltages for application to the comparator circuit in response to receiving command signals from a microprocessor. The comparator circuit generates a third lesser plurality of output signals, less than the second plurality, indicative of the status of a multiplicity of remote trunk circuits connected to the telephone lines. The circuit is inexpensive and occupies little circuit board area.

Abstract: The circuit of the present invention detects variations of a current I.sub.L flowing in a telephone line LL. A low-value resistor r is connected in series with line LL. A constant voltage generator is connected across this resistor. The current Is applied to resistor r by the contant voltage generator varies as a function of I.sub.L. This being so, a measurement of the variations of Is will reflect variations of I.sub.L and, therefore, can be used to detect both amplitude and directional variations of I.sub.L.

Abstract: A tip-ring interface that utilizes a single detector to detect ringing, forward loop current, and reverse loop current. In one embodiment, forward or reverse battery state may be detected when on-hook.

Abstract: A circuit for connection into a telephone line for detecting when a telephone instrument has gone off-hook and which is unaffected by the presence of a ringing signal on the telephone line. The circuit comprises a transistor switch, a first plurality of series connected diodes connected in series with the telephone line for developing a first voltage thereacross when the telephone instrument has gone off-hook, an RC circuit coupled to the first plurality of diodes for charging to the first voltage when the telephone instrument has gone off-hook after a time delay and for activating the switch, a second plurality of series connected diodes, the second plurality being greater than the first plurality, the second plurality of diodes being connected to the switch and to the first plurality of diodes for developing a second voltage thereacross during one half cycle of a ringing signal on the telephone line.

Abstract: An improved offhook supervision circuit including an amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The amplifier is arranged to develop and output a loop voltage signal representing the level of the DC signals applied to the subscriber loop circuit. A comparator device has a first input connected to the amplifier and is arranged to receive the loop voltage signal output by the amplifier. A second input of the comparator device is connected to a reference voltage device which outputs a predetermined reference signal voltage. Any significant reduction of the DC signal level on the loop circuit will cause the loop signal voltage output by the amplifier to fall below the reference signal voltage. An offhook signal is then output from the comparator device to a control device signaling an offhook condition.

Abstract: In a facsimile communication system, a call signal detecting device for identifying call signals which are received over a network. Both an unsounding call signal and a sounding call signal are detected by a single detection circuitry, which is also responsive to off-hooking of an own station's telephone set. Detection of such signals is implemented by the measurement of a period which is performed by a processing unit, so that changes in the specifications of the signals to be detected can be accommodated merely by modifying a program of the processing system and not the hardware of the device.

Abstract: An electronic switch for supplying power to a digital telephone which consumes substantially no power in the idle mode. A transistor for supplying power to the digital telephone is latched on in either of two situations. In the first situation, the telephone's hookswitch is closed. A second transistor turns on and maintains the first transistor on even after the hookswitch has been opened. In the second situation, a voltage pulse is applied to the input voltage conductor lines causing the first and second transistors to turn on. Again, the second transistor maintains the first transistor on. The circuit is inactivated by a sleep signal which turns off the second transistor which in turn turns off the first.

Abstract: A fast response electronic switch used for control of connect and disconnect functions, primarily related to speech network applications for electronic-microprocessor based telephones utilizing dual tone multifrequency and/or universal pulse dial address signaling. Disclosed circuitry includes an active surge protector, a saturated transistor switch and bias circuit which exhibits a high AC impedance with respect to the telephone subscriber line.

Abstract: Disclosed is a channel unit for directly interconnecting a toll office multiplex line and a terminal unit line such as that of a private branch exchange (PBX) or a telephone station set, thereby eliminating the normal local end office interconnection. In particular, the channel unit interfaces the different signaling protocols of the two lines and generates call progress controls signals such as dial tone and audible ringing which are normally generated by the local end office. The channel unit comprises a converter for each line for converting the electrical interface signals representative of the busy and idle conditions of the line to logic levels also representative of the busy and idle conditions of the line. A predetermined series of these logic levels form a control signal that indicates the state of a call on the line.