Plural line selector apparatus for enabling selection of one of a plurality of telephone lines

A selector having a plurality of output circuits and a common circuit for selectively completing a current path between said common and one of said output circuits comprising:

• a first plurality of manually operable momentary contact switches, each of said first plurality being associated with one of a corresponding plurality of circuits to be connected to a common circuit;
• a corresponding plurality of bistable electronic switch means, said switch means normally in a first condition and operable to a second condition, each of said bistable electronic switch means including:
• a first input for enabling said electronic switch means to a first condition, and a second disable input for enabling said electronic switch means into a second condition;
• a first plurality of output switch means, each of said switch means responsive to the associated one of said bistable switch means being in the second condition for completing an electrical circuit between a corresponding circuit and said common circuit;
• a plurality of NAND gates, said plurality corresponding in number with said plurality of bistable switch means, each said NAND gate including a plurality of inputs and an output;
• a plurality of voltage inverter means, each one of said inverter means connected in between the output of a corresponding one of said NAND gates and said disable input of a corresponding one of said bistable electronic switch means;
• a plurality of resistor means corresponding in number to said plurality of bistable switch means;
• means connecting each resistor means between a source of voltage at one end and at the other end in circuit with one said contact switch means, to the input of the bistable electronic switch means associated with said contact switch means and to a NAND gate input of the respective ones of said plurality of NAND gates associated with the remaining bistable electronic switch means;
• bias resistor means connected between electrical ground potential and one input of each of said NAND gate means;
• hookswitch means;
• second resistor means having a substantially lesser resistance than said bias resistor means;
• means connecting said hookswitch means and said second resistor means in series circuit between said source of voltage and said same NAND gate inputs as said bias resistor means;
• said hookswitch means being in a normally open condition and operable when closed to complete a circuit between said source and said inputs to change the voltage thereat;
• additional momentary contact switch means having a normally open position and operable to a closed position, one contact thereof connected to electrical ground potential;
• voltage inverter means;
• means connecting the input of said inverter to the remaining contact of said additional switch;
• electronic switch means having an input and output and responsive to a high voltage at its input for switching from a first to a second condition and responsive to a low at its input for switching from the second condition to the first condition;
• means responsive to said electronic switch means being in said first condition for interrupting the circuit between said common and a selected one of said outputs;
• means connecting the output of said inverter to said input of said electronic switch means;
• a capacitor;
• means connecting one end of said capacitor in common circuit with said bias resistor means and said inputs of said NAND gates and means connecting the other end of said capacitor in circuit with said output of said inverter;
• and
• an electric circuit whereby operation of said additional switch means results in an open circuit between said common circuit and said output circuits and restoration thereof results in the generation of a low pulse to the input of all said NAND gates and any bistable switch means that is in the first condition is restored to the second condition.

A line selection device for coupling a telephone instrument circuit associated with a telephone instrument of the type having a hookswitch to a selected one of a plurality of trunk telephone line circuits comprising:

• a first plurality of manually operable spring-return single-pole single-throw selection switches, each of said switches containing a pair of electrical contacts in a normally open circuit for closing an electric circuit therethrough in response to placement to the switch operate condition, said plurality of selection switches corresponding in number to the plurality of output telephone lines with one of the switches being associated with a corresponding one of said trunk line circuits;
• a source of high voltage and a source of low reference voltage, one source being of a higher voltage level relative to the other;
• means connecting one contact of each selection switch to said source of low reference voltage;
• a first plurality of electromechanical relay means, said plurality corresponding in number to said plurality of selection switches and one of said relay means associated with one of said first switch means, each of said relay means including a winding, and a set of contacts normally open responsive to energization of said winding for operating to the closed position contact;
• each of said contact sets of said relays connected between a common circuit in said telephone instrument and a corresponding one of said plurality of trunk telephone line circuits;
• a corresponding first plurality of NPN type transistors, each of said plurality being associated with a corresponding one of said relay means in said first plurality of relay means, each of said transistors having a base, a collector, and an emitter;
• means connecting each relay winding electrically in series between said source of high voltage and the collector of a corresponding one of said transistors;
• a plurality of NAND gate latches, said plurality corresponding in number to said first plurality of switches and transistors with each NAND gate latch being associated with a corresponding one of said transistors and said switches, each of said NAND gate latches including a first input, a second input, and a first output, each said NAND gate latch means normally in a first condition having a low voltage at said second output and responsive to a low voltage at its first input for switching to a second condition having a high at its said second output and further responsive to a high applied at its second input for switching back to said first condition;
• means connecting said first output of each one of said plurality of NAND gate latches to the base of a corresponding one of said transistors for energizing said transistor means in response to the establishment of the corresponding NAND gate latch means in the second condition;
• a first plurality of resistor means corresponding in number to the number of NAND gate latch means, each having a first and a second end, one end of each resistor means being connected to said source of high voltage;
• a plurality of NAND gates corresponding in number to the plurality of NAND gate latches, each of said NAND gates having a plurality of separate inputs corresponding in number to said NAND gate latch means and an output, each of said NAND gates normally providing a low voltage at the output thereof and responsive to a low voltage at any one of its plurality of inputs for providing a high voltage at the output thereof;
• each one of said NAND gates being associated with a corresponding one of said NAND gate latch means;
• a first plurality of voltage inverter means, said plurality corresponding in number to said plurality of NAND gates, each of said inverter means containing an input and an output for providing a low voltage or a high voltage at the output thereof in response to the input thereof having applied thereto either a high voltage or low voltage, respectively, each one of said inverter means having an input coupled to the output of a corresponding one of said NAND gates and its output connected to said second input of a corresponding one of said NAND gate latch means;
• means coupling said remaining end of each one of said first plurality of resistor means electrically in common with the remaining contact of a corresponding one of said selector switch means, said first input of a corresponding one of said NAND gate latch means and one input of each of those of said NAND gate means not associated with said respective one of said NAND gate latch means, whereby operation of a selector switch means associated therewith applies a low voltage to said first input of said NAND gate latch means associated therewith and to one input of each of the non-associated NAND gates;
• bias resistor means connected at one end to said low source;
• means connecting the remaining end of said bias resistor means electrically in common to one separate input of each of said NAND gate means;
• means for connecting said source of high voltage in circuit with one end of said hookswitch of said telephone instrument, said hookswitch means, normally open, for closing an electrical circuit upon removal of a telephone handset from its cradle;
• second resistor means, said second resistor means having a substantially lesser resistance than said bias resistor means;
• means for connecting the remaining end of said hookswitch means and said second resistor means in an electrical series to the remaining end of said bias resistor.