Telephone set identification system using reverse polarity interrogation signal

Claim 2

A party telephone identification system comprising: a central office including a central office battery; a multiparty subscriber''s line connected into said central office; a plurality of telephone sets connected to said line, each said set having on hook and off hook conditions; circuit means in said central office for connecting said battery to said line to apply a normal polarity of potential across said line and for reversing the polarity of potential across said line; electrical signal generating means connected in each of said sets, so that when a set is in the off hook condition and said central office potential applies said reverse polarity to said line, said signal generating means generates and transmits an identification oscillatory signal unique to said off hook set to the central office.

Claim 3

A party identification system as set forth in claim 1 wherein: said electrical signal generating means includes at least one inductance, resistance, capacitance tuned circuit for providing an oscillator signal of a predetermined frequency when said reverse polarity battery potential is applied to said telephone line.

Claim 4

In a telephone system, a telephone set, a line connecting said telephone set to a central office, circuit means in said central office for applying a first polarity battery potential to said line, circuit means for reversing the polarity of the battery potential, and means in said telephone set responsive to said reverse polarity battery potential when the telephone set is in the off hook condition for transmitting an oscillatory identification signal to said central office.

Claim 5

In a telephone system, a telephone set, a line connecting said telephone set to a central office, circuit means in said central office for applying a first polarity battery potential to said line, circuit means for reversing the polarity of the battery potential, and means in said telephone set responsive to said reverse polarity battery potential when the telephone set is in the off hook condition for transmitting an oscillatory identification signal to said central office.

Claim 6

A telephone system as defined in claim 3 wherein said means in said telephone set includes an oscillator circuit connected to the telephone line via the telephone set hookswitch contacts and said oscillator circuit oscillates in response to said reverse polarity battery potential.

Claim 7

A telephone system as defined in claim 4 wherein said means in said telephone set includes a multifrequency oscillator circuit coupled to a pushbutton dial to provide multifrequency dial signals when receiving the first polarity of battery potential and circuit means coupled to said oscillator circuit for rendering the oscillator automatically responsive to said reverse polarity battery potential.

Claim 8

A telephone system as defined in claim 4 wherein said oscillator circuit generates a plurality of frequencies during the presence of said reverse polarity signal.

Claim 9

In a telephone subset including a pair of hookswitches, a multifrequency semiconductor oscillator ciRcuit having a pair of tuned inductance-capacitance circuits with a plurality of switches for changing the resonant frequency of the tuned circuits to control the frequency of oscillation, an a pushbutton dial connected to the plurality of switches for selectively closing a switch in each of the tuned circuits each time a pushbutton is depressed, the improvement comprising: circuit means shunting one of the plurality of switches in at least one of said tuned circuits; switching means having first and second states of operation; means coupling said switching means to said pushbutton dial so that said switching means is switched from said first state to said second state while a pushbutton is depressed, and circuit means connecting said oscillator circuit to said pair of hookswitches through said switching means so that the connection between said oscillator circuit and said pair of hookswitches is reversed when said switching means is switched from said first state to said second state, the arrangement is such that with telephone hookswitches in the off hook condition and a first polarity of potential applied between the pair of hookswitches, said semiconductor oscillator circuit is unoperative until a dial pushbutton is depressed, and with a second polarity of potential opposite said first polarity applied between the pair of hookswitches and the oscillator circuit is energized to oscillate at a frequency corresponding to the tuned circuit having shunt circuit means.

Claim 10

In a telephone subset including a pair of hookswitches, a multifrequency semiconductor oscillator ciRcuit having a pair of tuned inductance-capacitance circuits with a plurality of switches for changing the resonant frequency of the tuned circuits to control the frequency of oscillation, an a pushbutton dial connected to the plurality of switches for selectively closing a switch in each of the tuned circuits each time a pushbutton is depressed, the improvement comprising: circuit means shunting one of the plurality of switches in at least one of said tuned circuits; switching means having first and second states of operation; means coupling said switching means to said pushbutton dial so that said switching means is switched from said first state to said second state while a pushbutton is depressed, and circuit means connecting said oscillator circuit to said pair of hookswitches through said switching means so that the connection between said oscillator circuit and said pair of hookswitches is reversed when said switching means is switched from said first state to said second state, the arrangement is such that with telephone hookswitches in the off hook condition and a first polarity of potential applied between the pair of hookswitches, said semiconductor oscillator circuit is unoperative until a dial pushbutton is depressed, and with a second polarity of potential opposite said first polarity applied between the pair of hookswitches and the oscillator circuit is energized to oscillate at a frequency corresponding to the tuned circuit having shunt circuit means.

Claim 11

A telephone set as defined in claim 7 wherein: said switching means includes first and second single-pole double-throw switches, each having a movable contact and a pair of stationary contacts, and wherein separate ones of the stationary contacts of each switch is connected to a different one of said pair of hookswitches; said oscillator circuit includes a transistor; said circuit means connects the collector and emitter electrodes of said transistor circuit to the movable contacts of said first and second switches, respectively, and said coupling means couples the movable contacts of the first and second switches to all the dial pushbuttons.

Claim 12

A telephone subset as defined in claim 7 wherein: a separate circuit means is connected to shunt one of the plurality of switches in each of said tuned circuits so that when said second polarity of potential is applied between said hookswitches said oscillator circuit generates the frequency corresponding to the dial frequency of the two shunted switches.

Claim 13

In a telephone subset as defined in claim 9 wherein: said separate circuit means comprises a series resistor and capacitor circuit.

Claim 14

In a telephone subset as defined in claim 9 wherein: said separate circuit means comprise a pair of normally closed switches coupled to said pushbutton dial to be opened each time a pushbutton is depressed.

Claim 15

In a rotary dial type telephone, the improvement comprising: a pair of terminals for connection to a telephone exchange; a hookswitch having off hook and on hook conditions connected to said pair of terminals; a semiconductor oscillator circuit; a tuned circuit including an inductor and a capacitor, inductively coupled to said oscillator circuit for determining the frequency of oscillation, and circuit means coupling said oscillator circuit to said hookswitch so that when said hookswitch is in an off hook position and the normal polarity of energizing potential across said pair of terminals is reversed, said oscillator circuit is energized to break into oscillation and apply the oscillation signals to said pair of terminals.

Claim 16

In a rotary dial type telephone, the improvement comprising: a pair of terminals for connection to a telephone exchange; a hookswitch having off hook and on hook conditions connected to said pair of terminals; a semiconductor oscillator circuit; a tuned circuit including an inductor and a capacitor, inductively coupled to said oscillator circuit for determining the frequency of oscillation, and circuit means coupling said oscillator circuit to said hookswitch so that when said hookswitch is in an off hook position and the normal polarity of energizing potential across said pair of terminals is reversed, said oscillator circuit is energized to break into oscillation and apply the oscillation signals to said pair of terminals.