Intercommunication and remote unit selection system employing a minimum of interconnecting wire

Claim 2

A multi-unit intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, said system comprising: a set of conductors; said central unit and each of said remote units having a first terminal and a second terminal and a two-way audio circuit connected between said first and second terminals of said units; the terminals of each of said remote units being connected across unique pairs of conductor''s of said set; selection means for selectively connecting the first and second terminals of said central unit each to a different conductor of said set to complete a two-way communications path through the audio circuits of the selected remote unit and said central unit and along the unique pair of wires connecting said selected remote unit; signaling means at each of said remote units for applying a control signal across the first and second terminals of said remote unit; control means at said central unit for initiating a control operation at said central unit in response to the control signal from the selected remote unit; and a reversible audio amplifying unit connected to the audio circuit of said central unit; and said control means being operative to control the direction of said reversible amplifying unit.

Claim 3

An intercom system according to claim 1 wherein: said set of conductors includes a first group of conductors connected only to the first terminals of said remote units and a second group of conductors connected only to the second terminals of said remote units; said selection means includes means for connecting the first terminal of said central unit to one of the conductors of said first group and means for connecting said second terminal of said central unit to one of the conductors of said second group.

Claim 4

An intercom system according to claim 2 wherein said system further comprises: a uni-directional circuit element connected in the same orientation in each of said remote units and in series with the audio circuit of said remote unit to permit current to flow only in a direction from said first to said second terminal of each of said remote units; and means at said central unit for applying a DC bias potential across the terminals of said central unit, said bias means including a positive lead connected to the first terminal of said central unit and a negative lead connected to said second terminal of said central unit; whereby, only the selected one of said remote units is rendered conductive to an audio signal.

Claim 5

An intercom system according to claim 1 further comprising: a releasable door latch at said central unit; said control means at said central unit being operative to release said door latch in response to a control signal from said selected remote unit.

Claim 6

An intercom system according to claim 1 wherein: said signaling means at said remote unit includes means for varying a DC voltage at said central unit; and said control means at said central unit includes means responsive to a DC voltage level change to initiate said control operation.

Claim 7

An intercom system according to claim 5 wherein each of said remote units comprises: a speaker coil and a capacitor connected in series in said audio circuit; and a variable resistance network connected in parallel across said audio circuit and including switching means operative to selectively connect different resistances into said resistive network to vary the DC impedances across the terminals of said remote unit.

Claim 8

An intercom system according to claim 5 wherein each of said remote units comprises: a variAble resistance network connected between the terminals of said remote unit and including switching means operative to selectively connect different resistances into said resistive network to vary the DC impedances across the terminals of said remote unit.

Claim 9

An intercom system according to claim 1 further comprising: means at said central unit for applying a call signal across the terminals of said central unit; means connected at said central unit operative to interrupt said communications path between said central and selected remote unit; time delay control means operatively connected to said interrupting means to close the communications path in response to a reset signal and to break said communications path at some predetermined time sufficient for a response to some signal from said remote unit.

Claim 10

An intercom system according to claim 5 wherein said control means at said central unit is responsive to the timed duration of a control signal from said remote unit to initiate a control function.

Claim 11

An intercom system according to claim 1 further comprising: a sneak path preventing circuit at each of said remote units, including a uni-directional conducting device and a zener diode reverse connected in series with said uni-directional conducting device and said audio circuit; said sneak path preventing circuit being oriented to permit conduction only from said first to said second terminal of each of said remote units; conductors of said set being connected to the first terminal of some of said remote units and to the second terminals of others of said remote units.

Claim 12

An intercom system according to claim 10 further comprising: means at said central unit for applying a bias voltage across the terminals of said central unit, said bias voltage being from one to two times the reverse voltage of said zener diodes, whereby said bias voltage is sufficient to complete a path through one and only one of said remote units.

Claim 13

An intercom system according to claim 11 wherein said bias voltage is from: one time the reverse voltage of the zener diodes plus the amplitude of said audio signal, to: two times the reverse voltage of said zener diodes minus the amplitude of said audio signal.

Claim 14

An intercom system according to claim 11 wherein: said selector means is effective to connect a unique remote unit in a communication path with said central unit by uniquely applying a signal of a given polarity across a selected pair of conductors of said set.

Claim 15

A multi-unit intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, said system comprising: a first set of conductors; each of said units having a first terminal and a second terminal; the terminals of each of said remote units being connected across a different pair of conductors of said first set so as to provide a unique conductive path therebetween; some of said conductors being connected to the first terminal of at least one remote unit and a second terminal of at least one other remote unit; first selection means for selectively connecting the terminals of said central unit each to a different conductor of said set of a selected remote unit and said central unit; a potential source connectable across the terminals of said central unit; a sneak path preventing circuit at each of said remote units, including a uni-directional conducting device and a zener diode reverse connected in series between the terminals of each of said remote units; and said sneak path preventing circuit being oriented to permit conduction only from said first to said second terminal of each of said remote units.

Claim 16

A multi-unit intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, said system comprising: a first set of conductors; each of said units having a first terminal and a second terminal; the terminals of each of said remote units being connected across a different pair of conductors of said first set so as to provide a unique conductive path therebetween; some of said conductors being connected to the first terminal of at least one remote unit and a second terminal of at least one other remote unit; first selection means for selectively connecting the terminals of said central unit each to a different conductor of said set of a selected remote unit and said central unit; a potential source connectable across the terminals of said central unit; a sneak path preventing circuit at each of said remote units, including a uni-directional conducting device and a zener diode reverse connected in series between the terminals of each of said remote units; and said sneak path preventing circuit being oriented to permit conduction only from said first to said second terminal of each of said remote units.

Claim 17

An intercom system according to claim 14 wherein: the potential of said potential source is from one to two times the reverse voltage of said zener diodes, whereby said potential is sufficient to cause a conductive path to be completed through oNe and only one of said remote units.

Claim 18

An intercom system according to claim 15 wherein: each of said remote units includes an audio circuit connected between the terminals of each of said remote units; and said potential is from: one times the reverse voltage of said zener diodes plus the amplitude of said audio signal to: two times the reverse voltage of said zener diodes minus the amplitude of said audio signal.

Claim 19

An intercom system according to claim 16 wherein: said audio circuit of each of said units is connected in series with the zener diode, and the uni-directional conducting device thereof.

Claim 20

An intercom system according to claim 15 wherein: said system is effective to connect a specified unique remote unit in a communication path with said central unit by uniquely applying a signal of a given polarity across the combination of two conductors of said set to which said specified unique remote unit is connected, whereby said specified unique remote unit becomes said selected remote unit.

Claim 21

An intercom unit according to claim 14 further comprising: a pair of audio conductors extending from said central unit to each of said remote units; said central unit including an audio circuit connected between said audio conductors; each of said remote units including an audio circuit, a load connected in series with said zener diode and said unidirectional conducting device, and switching means for connecting said audio circuit to said audio conductors when said load is energized.

Claim 22

An intercom system according to claim 14 wherein: the unidirectional conducting device of each of said remote units being the base to emitter path of a transistor; each of said remote units including a third terminal, the collector of said transistor being connected to said third terminal; said central unit including a third terminal and conductor means for interconnecting said central unit third terminal and the third terminal of said remote unit, and said potential source is further connectable between said central unit third terminal and one of said first and second terminals of said central unit.

Claim 23

A system according to claim 20 wherein said conductor means includes: a second set of conductors, each of the conductors of said second set being connected to the third terminals of different groups of remote units; and second selection means for connecting said third terminal of said central unit with a selected one of the conductors of said second set.

Claim 24

An intercom system according to claim 21 wherein: each of those remote units which have their third terminals connected to the same one of the conductors of the said second set, has its first and second terminals connected in a unique current conducting path across a combination of two of the conductors of said first set.

Claim 25

An intercom system according to claim 21 wherein: said first set of conductors includes a plurality of identical sub-sets of conductors; each of said sub-sets of conductors having different sets of remote units connected thereto; and said first selection means including switching means for selectively connecting said sub-sets of conductors to said central unit terminals.

Claim 26

An intercom system according to claim 14 wherein each of said units includes an audio circuit, and the system further comprises: calling means at said control unit for momentarily connecting said potential source across said central unit first and second terminals; and latching means at each of said remote units operative to connect the audio circuit of the selected remote unit to the audio circuit of said central unit in response to a potential being applied across the terminals of said selected remote unit.

Claim 27

An intercom system according to claim 24 further comprising: a pair of audio conductors separate from the conductors of said sets for connecting the audio circuits of each of said remote units in parallel across the audio circuit of said central unit.

Claim 28

An intercom system according to claim 25 wherein: said latching means includes a holding circuit through said audio conductors.

Claim 29

An intercom system according to claim 26 wherein: each of said remote units includes a selective impedance network for varying the impedance between two of the terminals of the remote unit to generate control signals to said central unit.

Claim 30

An intercom system according to claim 27 wherein: said central unit includes a knock-down timer operative to break said holding circuit at a predetermined delay time after said timer has been set, said timer being set in response to the operation of said calling means and in response to certain of said control signals.

Claim 31

An intercom system according to claim 27 wherein: said central unit includes a reversible audio amplifying unit responsive to certain control signals from said remote unit to establish its direction of operation.

Claim 32

An intercom system according to claim 27 wherein: said central unit includes means for disabling said central unit audio circuit until certain signals from said remote unit are received at said central unit.

Claim 33

An intercom system according to claim 14 wherein each of said units includes an audio circuit and said system further comprises: calling means, at said central unit, including normally opened momentary switch means connected in series with said potential source between the first and second terminals of said central unit; a pair of audio conductors connecting the audio circuits of each of said remote units across the audio circuit of said central unit; a normally opened switch, at each of said remote units, connected between the remote unit audio circuit and said audio conductors; a switch actuating circuit, at each of said remote units, connected between the remote unit first and second terminals, and being energized to close said switch when said switch means of said calling means is closed; a holding circuit for energizing the switch actuating circuit of a remote unit when the remote unit switch is closed, said holding circuit including means connecting the actuating circuit with the remote unit audio circuit at each remote unit and means connecting the central unit audio circuit with the potential source; and means for breaking said holding circuit to open said switch.

Claim 34

An intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, each having an audio circuit, said system comprising: a first set of conductors; each of said units having a first terminal and a second terminal; each of said remote units having its terminals connected across a different pair of conductors of said first set; a potential source connected between the first and second terminals of said central unit; calling means including normally opened switch means for selectively connecting said source between conductors of said first set to thereby apply an energizing potential across the first and second terminals of the selected remote unit; a pair of audio conductors connecting the audio circuits of each of said remote units across the audio circuit of said central unit; a normally opened switch, at each of said remote units, connected between the remote unit audio circuit and said audio conductors; a switch actuating circuit, at each of said remote units, connected between the remote unit first and second terminals, and being energized to close said switch when said switch means of said calling means is closed; a holding circuit for energizing the switch actuating circuit of a remote unit when the remote unit switch is closed, said holding circuit including means connecting the actuating circuit with the remote unit audio circuit at each remote unit and means connecting the central unit audio circuit with the potential source; and means for breaking said holdIng circuit to open said switch.

Claim 35

An intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, each having an audio circuit, said system comprising: a first set of conductors; each of said units having a first terminal and a second terminal; each of said remote units having its terminals connected across a different pair of conductors of said first set; a potential source connected between the first and second terminals of said central unit; calling means including normally opened switch means for selectively connecting said source between conductors of said first set to thereby apply an energizing potential across the first and second terminals of the selected remote unit; a pair of audio conductors connecting the audio circuits of each of said remote units across the audio circuit of said central unit; a normally opened switch, at each of said remote units, connected between the remote unit audio circuit and said audio conductors; a switch actuating circuit, at each of said remote units, connected between the remote unit first and second terminals, and being energized to close said switch when said switch means of said calling means is closed; a holding circuit for energizing the switch actuating circuit of a remote unit when the remote unit switch is closed, said holding circuit including means connecting the actuating circuit with the remote unit audio circuit at each remote unit and means connecting the central unit audio circuit with the potential source; and means for breaking said holdIng circuit to open said switch.

Claim 36

An intercom system according to claim 32 wherein: said central unit has a third terminal, each of said remote units includes a third terminal and a relay; third terminal conductor means for connecting said third terminal of said remote unit to the third terminal of said central unit; each of said switch actuating circuits includes a transistor and the winding of said relay, said relay winding being connected between said third terminal and the collector of said transistor; the base of said transistor is connected to the second terminal of said remote unit and the emitter of said transistor is connected to the first terminal of said remote unit; and said switch includes the contacts of said relay.

Claim 37

An intercom system according to claim 33 wherein: said first set of conductors includes a first sub-set of conductors connected to the first terminals of said remote units and a second sub-set of conductors connected to the second terminals of said remote units; and said system further comprises a first selector for selectively connecting the first terminal of said central unit with a conductor of said first sub-set, and a second selector for selectively connecting the second terminal of said central unit with a conductor of said second set.

Claim 38

An intercom system according to claim 34 further comprising: said third terminal conductor means which includes a third sub-set of conductors connected to the third terminals of said remote units; and a third selector for selectively connecting the third terminal of said central unit with a conductor of said third sub-set.

Claim 39

An intercom system according to claim 35 wherein: one of said sub-sets includes a plurality of groups of conductors connected to different groups of remote units, and said system further includes a group switch for connecting said group of conductors to the corresponding sub-set selector; and said system includes a fourth selector for selectively actuating one of said group switches.

Claim 40

An intercom system according to claim 32 wherein: the switch means of said calling means includes a set of momentary switches each connected between one terminal of said central unit and the first terminal of a different one of said remote units.

Claim 41

An intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, wherein: each of said units includes a first terminal, a second terminal, a third terminal, and an audio circuit; said central unit includes an audio circuit, and a potential source connectable from said first terminal to said second and third terminals; each of said remote units includes a transistor switch for connecting the remote unit audio circuit to the audio circuit of said central unit, said transistor having its emitter connected to the remote unit first terminal, its base connected to the remote unit second terminal, and its collector connected to the remote unit third terminal; said system includes a first set of conductors connecting to the first terminals of said remote units, a second set of conductors connecting to the second terminals of said remote units, and a third set of conductors connecting to the third terminals of said remote units; and said system further includes a first selector for connecting one conductor of said first set to the first terminal of said central unit, a second selector for connecting one conductor of said second set to the second terminal of said central unit, and a third selector for connecting one conductor of said third set to the third terminal of said central unit.

Claim 42

An intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, wherein: each of said units includes a first terminal, a second terminal, a third terminal, and an audio circuit; said central unit includes an audio circuit, and a potential source connectable from said first terminal to said second and third terminals; each of said remote units includes a transistor switch for connecting the remote unit audio circuit to the audio circuit of said central unit, said transistor having its emitter connected to the remote unit first terminal, its base connected to the remote unit second terminal, and its collector connected to the remote unit third terminal; said system includes a first set of conductors connecting to the first terminals of said remote units, a second set of conductors connecting to the second terminals of said remote units, and a third set of conductors connecting to the third terminals of said remote units; and said system further includes a first selector for connecting one conductor of said first set to the first terminal of said central unit, a second selector for connecting one conductor of said second set to the second terminal of said central unit, and a third selector for connecting one conductor of said third set to the third terminal of said central unit.

Claim 43

An intercom system according to claim 38 wherein: the different conductors of one of said sets correspond to different floors of an apartment building.

Claim 44

An intercom system according to claim 38 further comprising: a plurality of remote termination units arranged in groups and eAch having an audio circuit; said first recited remote units being remote switching units operable, when energized, to connect the audio circuits of the termination units of a unique one of said groups to the audio circuit of said control unit, a fourth set of conductors; each of said remote termination units having a first terminal and a second terminal, a normally-opened switch connected in the termination unit audio circuit, and means connecting between the remote termination unit first and second terminals operative when energized to close said switch; each of the conductors of said fourth set being connected to the first terminal of one remote termination unit of each of said groups; the second terminals of each of said remote termination units of each group being interconnected; said central unit having a fourth terminal, a potential source being connected between said fourth terminal and the audio circuit of said central unit; and a fourth selector for selectively connecting said central unit fourth terminal to one of the conductors of said fourth set.

Claim 45

An intercom system according to claim 40, wherein: the conductors of said fourth set correspond to different floors of an apartment building; said system further comprising a plurality of switches and each corresponding to vertical columns of apartment units each operable in response to a unique combination of settings of said first, second and third selectors, each unit being located on a different floor of the apartment building.

Claim 46

An intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, each of said units having an audio circuit, said system comprising: a plurality of switch units, each having a first terminal, a second terminal, and a third terminal, each of said switch units being actuated when all of the three terminals thereof are energized; each of said switch units being operable when actuated to connect the audio circuits of a unique group of remote units to the audio circuit of said central unit; and selection means for selectively actuating said switch units by selectively energizing all of the three terminals of a selected one of said switch units.

Claim 47

An intercom system for communicating with an audio signal between a central unit and any one of a plurality of remote units, each of said units having an audio circuit, said system comprising: a plurality of switch units, each having a first terminal, a second terminal, and a third terminal, each of said switch units being actuated when all of the three terminals thereof are energized; each of said switch units being operable when actuated to connect the audio circuits of a unique group of remote units to the audio circuit of said central unit; and selection means for selectively actuating said switch units by selectively energizing all of the three terminals of a selected one of said switch units.

Claim 48

An intercom system according to claim 42 wherein: said central unit includes a first terminal, a second terminal, and a third terminal; said central unit includes a potential source connectable between said first terminal and both said second and third terminals; each of said switch units includes a transistor switch operative when energized to actuate said switch unit to connect the audio circuits of the selected group of remote units to the audio circuit of said central unit, said transistor having its emitter connected to the switch unit first terminal, its base connected to the switch unit second terminal, and its collector connected to the switch unit third terminal; said system includes a first set of conductors connecting to the first terminals of said switch units, a second set of conductors connecting to the third terminals of said switch units, and a third set of conductors connecting to the third terminals of said switch units; and said system further includes a first selector for connecting one conductor of said first set to the first terminal of said central unit, a second selector for connecting one conductor of said second set to the second terminal of said central unit, and a third selector for connecting one conductor of said third set to the third terminal of said central unit.

Claim 49

An intercom system according to claim 43 further comprising: a fourth set of conductors; each of said remote units having a first terminal and a second terminal, a normally opened switch connected in the remote unit audio circuit, and means connecting between the remote unit first and second terminals operative when energized to close said switch; each of the conductors of said fouRth set being connected to the first terminals of remote units of different groups of remote units; the second terminals and the audio circuits of each of said remote units being interconnected; said central unit having a fourth terminal and means for applying potential between said fourth terminal and the audio circuit of said central unit; and a fourth selector for selectively connecting said central unit fourth terminal to one of the conductors of said fourth set.

Claim 50

An intercom system according to claim 44, wherein: the conductors of said fourth set correspond to different floors of an apartment building and the riser switches correspond to vertical columns of apartment units, each located on a different floor of the apartment building.