Abstract: A D/A converter having a feedback capacitor C1 between the inverting input and output of an operational amplifier A1 having a virtual ground on the inverting input. First switch means is sequentially responsive to binary values of bits of a digital input word for connecting a bus line to either a reference voltage or ground. Second switch means alternately connects opposite sides of a second capacitor C2.dbd.C1 between ground and the bus line for sampling the logic level of a bit, and across C1 for redistributing sampled charge during each bit. The charge on C1 is transferred to a storage capacitor and then reset to zero at the end of each word. In an alternate embodiment, one of a pair of switched capacitors samples the logic level while the other is connected across C1 for redistributing stored charge. In another embodiment, binary weighted capacitors sample the logic levels of bits in pairs and are simultaneously connected across C1 for redistributing charge.

Abstract: A D/A converter having a feedback capacitor C1 between the inverting input and output of an operational amplifier A1 having a virtual ground on the inverting input. First switch means is sequentially responsive to binary values of bits of a digital input word for connecting a bus line to either a reference voltage or ground. Second switch means alternately connects opposite sides of a second capacitor C2=C1 between ground and the bus line for sampling the logic level of a bit, and across C1 for redistributing sampled charge during each bit. The charge on C1 is transferred to a storage capacitor and then reset to zero at the end of each word. In an alternate embodiment, one of a pair of switched capacitors samples the logic level while the other is connected across C1 for redistributing stored charge. In another embodiment, binary weighted capacitors sample the logic levels of bits in pairs and are simultaneously connected across C1 for redistributing charge.

Abstract: A remote time and charge system for use in conjunction with a telephone traffic service position system is shown. This system provides each hotel or motel with an automated print out of the duration of a particular call, the identity of the particular caller within the hotel or motel and the charges to be applied to the particular call. As a result, no attendant is required at each hotel or motel to monitor long distance calls and request time and charge information for each of them.

Abstract: An interrupt expander circuit provides for greatly enlarging the capacity of vectored interrupts in a microprocessor system. This circuit provides the capability for a very large number of peripheral devices to be connected to a microprocessor centeral processing unit via an interrupt structure while maintaining the same interface requirements between the interrupting peripheral devices and the microprocessor. This circuit provides a priority interrupt structure.

Abstract: An arrangement for mounting a dual-in-line packaged integrated circuit (DIP) to a thick/thin film circuit wherein a portion of each DIP lead is formed into a U-shape including a horizontal foot portion. The arrangement further includes a complementary socket which accepts the U-shaped DIP leads in opposite sides thereof. The socket is then soldered to either a thick/thin film circuit of a circuit board.

Abstract: An active filter used for the loop filter of a phase-lock loop has one input to the operational amplifier thereof connected to receive the output from a phase detector, and has the non-inverting input connected to receive a control signal from an override signal generator. Under normal operating conditions, the output from the override signal generator is such that it does not affect operation of the active filter and the filter operates as a standard loop filter. During abnormal operating conditions the output signal from the override signal generator is of such magnitude that it causes the operational amplifier and, hence, the filter to output the maximum voltage +V. The filter output is connected to one end of a pair of serially connected resistors which have the node connected to the control voltage input of the voltage control oscillator. The other end of the serially connected resistors is connected to the collector of a transistor.

Abstract: A digitally activated ringing circuit for use in conjunction with a central processing unit of an electronic telephone central office is connected between the central processing unit and a telephone subscriber via the central office switching network. The ringing circuit generates an analog signal representing a particular one of a plurality of possible ringing frequencies to be applied to the subscriber line. The instantaneous values of the ringing signal are approximated by information contained within a read only memory.

Abstract: An improved conference circuit for use in a Pulse Code Modulation telephone switching system wherein a number of channels are combined so that a number of subscribers may participate in a common telephone conversation. The conference circuit is provided with a multi-frame voice level summing arrangement whereby spurious channel switching caused by noise peaks is effectively eliminated.

Abstract: The present invention is a call processing monitor circuit for dynamically verifying the operation of a telephone switching center. This system provides for continuously testing a telephone switching center's ability to process telephone traffic. This is accomplished by placing telephone calls one at a time from various network inlets to various network outlets in the switching center. For the detection of a predetermined number of consecutive failures, an output alarm signal is generated by the system.

Abstract: A billing interface circuit for controlling the billing of a station of a private branch exchange via a telephone central office. This circuit automatically connects an intercept recorder to the operator requesting time and charges while providing ring back tone to the station. Therefore, the attendant at the private branch exchange is relieved of the task of manually interfacing between the station and the telephone central office to request time and charges information for billing.

Abstract: A switching device comprising a spring pile-up assembly including a plurality of pairs of cantilevered stationary and movable contact springs secured between a pair of support members. A follower card is slidably mounted on the top portions of the support member allowing the follower to move in a plane 90 degrees to the contact springs. The tips of the movable contact springs protrude through openings in the follower card. A cam card including cam portions is slidably mounted to one of the support members perpendicular to the follower. As the cam card is moved the cams engage an edge of the follower causing it to be displaced in its plane of motion sufficiently to open a selected number of contact springs while allowing another selected number of contact springs to close.

Abstract: The present invention is a call processing monitor circuit for dynamically verifying the operation of a telephone switching center. This system provides for continuously testing a telephone switching center's ability to process telephone traffic. This is accomplished by placing telephone calls one at a time from various network inlets to various network outlets in the switching center. For the detection of an alternate failure pattern, an output alarm signal is generated by the system.

Abstract: A digital intercept recorder/announcer system for use in conjunction with a telephone central office. The system performs the function of recorded message announcement for messages such as wrong number, time or weather announcements. The system samples and digitizes audio input signals from local or remote audio sources. Sampled data is stored in sequential fashion in memory so that it may be read out of memory exactly as it was stored. Upon demand, these stored signals are retrieved from memory, reconverted to an analog form and coupled to a subscriber's line for audio transmission to the subscriber. Delta modulation techniques are employed in the system.

Abstract: A mechanism for automatically restoring an operated and depressed pushbutton line key in a multi-line key telephone instrument. When the telephone instruments handset is returned to the instruments cradle, the cradle rotates a cradle shaft which in turn rotates a hookswitch and a restoral actuator mounted to the shaft. The hookswitch actuator operates hookswitch contact springs placing the instrument in the "on-hook" condition and simultaneously the restoral actuator moves a button restoral arm which swings horizontally about a pivot. Restoral linkage mounted to the restoral arm transfers the arms' motion to an interlock lever which also pivots applying a mechanical force on the line key latch bar, unlatching the depressed pushbutton and restoring it to its original or non-operated position.

Abstract: An interlock circuit is set forth which provides for controlling asynchronous data transfers between a host processor and a plurality of microprocessors via a common buffer. The interlock circuit consists of an interconnection of latches arranged so that the first processor initiating a transfer request inhibits all remaining processors from activating their respective transfer requests. Each processor upon terminating a data transfer clears its associated transfer request. The host processor can clear all transfer requests upon command.

Abstract: A digitally activated coin control circuit for use in combination with a digitally activated ringing circuit for common manipulation of a prepaid coin station by a central processing unit of a telephone switching center to collect and alternatively to refund deposited coins.

Abstract: A reed relay is constructed by first depositing a layer of an electrically conductive material substantially over an encapsulated reed switch. Terminals are laser welded to the conductive layer and a laser beam is used to cut a continuous pitch spiral from the conductive layer to simulate a conventional control winding.

Abstract: A telephone ringing signal generator which produces a signal that can ring a plurality of connected ringers tuned to different frequencies. The ringing signal comprises sequentially varying frequencies and each ringer will ring in response to its particular frequency. A counter is used to define the duration of the ringing signal and enable each frequency sequentially. A variable sweep frequency oscillator is connected to the counter and generates a signal having a different frequency for each counter increment. A programmable filter shapes the signal into a sine wave which is amplified to ringing voltage levels by a ringing signal amplifier.

Abstract: An integrated current source comprising a discrete resistor having one side thereof electrically connected through a PNP transistor to a first DC supply voltage and through series connected base-emitter diodes of a first pair of NPN transistors to a temperature stable DC supply voltage. The other side of the resistor is electrically connected to ground through series connected base-emitter junctions of a second pair of NPN transistors, with the base emitter junctions of the first and second transistor pairs being poled in opposite directions. The NPN transistors are caused to have collector currents that make the base-emitter junction voltages cancel on opposite sides of the resistor. This causes the temperature stable supply voltage to be established across the resistor in order to set a reference current in it, and in an NPN transistor driving the load, that is substantially constant and independent of temperature.

Abstract: An arrangement for locking a reed capsule within a tubular bobbin of a reed switch assembly comprising, a deflectable tab located adjacent a slot formed by two upstanding arms. The tab is disposed to deflect inward when a wire return strap connected to a reed capsule is inserted into the slot. When the reed capsule is fully seated within the bobbin the tab returns outward over the wire strap, locking the strap between the tab and the closed end of the slot.