Abstract: A precise temperature dependent voltage reference and voltage comparator comprising a three terminal circuit. When the input voltage exceeds a predetermined threshold, the output switches from the nonconducting, "off" state to a current conducting "on" state. The threshold condition can be tailored to a specific temperature characteristic and low voltage range with an input current on the order of 25 microamperes. With the output tied to the input, the circuitry can act as a reference diode.

Abstract: A circuit which prevents a telephone station from being used for unauthorized toll calls while allowing toll calls to be made when preceded by authorized passwords. When the telephone station is in the toll restriction mode of operation a microprocessor disconnects the tone generator from the keypad and provides audible and visual error signals upon detection of operation of the "0" or "1" keypad buttons. Upon detection of simultaneous operation of the "1" and "2" keypad buttons, the microprocessor provides audible and visual signals to prompt entry of a password. If a valid password is entered, the telephone station enters the unrestricted mode of operation and the toll restriction circuit is disabled until the handset is returned to the on-hook position after termination of the subsequent toll call.

Abstract: A voltage comparator with both analog and digital outputs. The analog output being useful to control a analog processer such as a voltage regulator while the digital output gives an indication of the controlled state. The present circuitry may be adapted as a lowcost means of adding microprocessor control to an ongoing process whose behavior is dependent upon the state of another parameter such as the voltage exhibited by a non-rechargeable battery supply.

Abstract: A secretarial answering system for use with a switching system which includes a plurality of subscriber telephone stations each equipped with a buzzer, and a secretarial telephone station equipped with an audible signalling circuit and a plurality of lamp and switch pairs. A first processing unit periodically scans line circuits to determine changes in the busy, idle or ringing status of the subscriber stations. A second processing unit converts status and line identification information from parallel to serial format, and transmits it to the secretarial station via a link bus protocol for packetized messages. The secretarial station then provides visual and audible indications of subscriber station status. The secretarial station transmits a switch initiated directed call pickup or a call transfer message to the switching system, and a buzzing requested message to the second processing unit.

Abstract: The present invention consists of a subcircuit which may be employed in integrated circuit technology to provide the necessary drop from a relatively high voltage source and to provide base current for biasing of associated transistorized circuitry. Each subcircuit employs four transistors and one resistor and provides an effective drop from approximately 1.1 volts when it is desired to provide at least 2 microamps of bias circuit. Additional subcircuits of similar configuration can be placed in series with the present circuitry to increase the amount of voltage drop in accordance with the requirements of the associated circuitry.

Abstract: A laminate switch assembly comprising dual dome switchplates providing improved tactile sensation good balance characteristics and able to maintain a low dynamic resistance throughout its life expectancy. Both tensioned domes are aligned with electrical contact areas part of which is formed on the underside of one dome and the other on a printed circuit board or backplate, which in response to depression are placed in contact with each other to provide a switch closure to a connected or associated electrical device.

Abstract: A technique for evaluating keypad conditions while utilizing only a minimum number of ports in a microprocessor involved in control of a telephone instrument. Because of the limited number of ports available and necessity to also evaluate conditions of mode selecting strap switches, the utilization of a reduced number of ports is highly desirable in such an enviroment. Such a reduction becomes an absolute necessity particularly in dealing in those enviroments that include random access memories, read only memories, pulse dialers, integrated circuits and liquid crystal displays. A combination of diode gating, resistive decoupling and time multiplexing techniques are used to match the input/output requirements to the available ports of a specific microprocessor.

Abstract: A hold circuit for use with a single line telephone operable over long or short telephone loops. The included circuit during response to the momentary operation of a manual switch actuates a silicon controlled rectifier to place a resistive load across the telephone line thus allowing the subscriber at the telephone instrument to go "on-hook". Subsequent removal of the basic instrument handset from the hook-switch, or of a related extension telephone going "off-hook", will cause the resistive load to be removed.

Abstract: A hookswitch mechanism for use in a telephone instrument utilizing a compound form cantilever spring fastened to a printed wiring card with circuit connections made to the printed wiring card. A contact engaging portion on the cantilever spring wipes across a contact located on the printed wiring card before disengaging the contact to insure a clean contact surface regardless of surrounding atmospheric conditions.

Abstract: An arrangement of mounting printed wiring boards providing reduced backplane conductor congestion. The printed wiring boards are mounted in columns and interconnected within a column by conductors on interconnect planes. Connections between interconnect planes and between external terminations and the interconnect planes are accomplished by conductors on backplanes which connect to the interconnect planes. Congestion of backplane conductors is avoided by routing connections, not terminating to external points, directly from one interconnect plane to another interconnect plane by means of conductors on a cross-connect board connecting the two interconnect planes. The arrangement also includes a column between the backplane and the printed wiring boards which are mounted at an angle to the horizontal. Air flows through this column to cool the printed wiring boards by means of convection.