US3728493A

US3728493A - Intercommunication system

Info

Publication number: US3728493A
Application number: US00121034A
Authority: US
Inventors: W Veen
Original assignee: Scovill Inc
Current assignee: NUTONE Inc MADISON AND RED BANK ROADS CINCINNATI OHIO 45227 A CORP OF DELAWARE
Priority date: 1971-03-04
Filing date: 1971-03-04
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17

Abstract

A two-way intercommunication system for selectively interconnecting a central station, such as an apartment or office lobby, with any one of a multiplicity of remote units, such as individual apartments or offices of a multi-unit building.

Description

Apr. 17, 1973 United States atem Ter Veen Auth Prahm...

S 60 67 99 i ll 11 INTERCOMMUNICATION SYSTEM 2,263,157 11/1941 2,536,820 1/1951 [75] Inventor. gfiillam B. Ter Veen,1C1nc1nnat1, 3,284,571 3,491,353 Assigncc: Scovill Manufacturing Company,

Waterbury, C Primary ExaminerRalph D. Blakeslee Assistant ExaminerThomas L. Kundert [22] Filed 1971 Att0meyWood, Herron & Evans [21] App]. No.: 121,034

ABSTRACT A two-way intercommunication system for selectively interconnecting a central station, such as an apartl79/37, l H; ment or office lobby, with any one of a multiplicity of 340/286 remote units, such as individual apanments or offices of a multi-unit building.

[51] Int. [58] FieldofSearch...............................

References Cited UNITED STATES PATENTS 3 Claims, 4 Drawing Figures 2,567,484 lvens l 79/3 7 REMOTE STA. OR UNIT DR, LOCK RELAY sw. OPTION CIRCUIT, DIRECTO'RY USE LAMP I I I l SIGNAL GENERATOR AUDIO TONE l CONTROL CRCUIT= REVERSE SWITCH A22 AMP.

SPEAKER RR. LOBBY INTERCOMMUNICATION SYSTEM This invention relates to intercommunication systems, and more particularly to intercommunication systems for facilitating two-way communication between a central station, such as the lobby of an apartment, office building or the like, and a selected one of a plurality of remote units, such as individual apartments or offices.

The utility of intercommunication systems which permit two-way communication between a central station, such as the lobby of an apartment or office building, and a plurality of remote stations, such as the individual apartments or offices of the building, is now well established and accepted. Such systems permit the tenant of an office or apartment to converse with a prospective visitor prior to permitting the visitor to enter the apartment or office, as the case may be. Such preliminary conversation provides the tenant with an opportunity to screen or interview the prospective visitor, and if so desired to deny entry. In certain instances, for example in the case of door-to-door salesmen, a housewife who normally would be too embarrassed to dismiss a salesman to whom she has opened the door without first subjecting herself to his sale appeal, finds it remarkably less embarrassing and significantly more convenient when using an intercommunication system to summarily dismiss the same salesman without a hearing. This the housewife does in the privacy and security of her apartment knowing the will never be nearer than a distant lobby.

From the standpoint of personal security, the preliminary screening of visitors afforded by intercommunication systems of the type to which this invention is directed permits a housewife to safely deny entry to a potential assailant who, in the absence of such screening, may easily have gained entry when the housewife unwittingly opened the door in response to what she believes is an innocent knock or ring of the doorbell.

Finally, intercommunication systems for an apartment or -office building are desirable from the standpoint of convenience alone. For example, a dairy products delivery-man can conveniently inquire of his customer as to the customers specific need for dairy products on a given day. This avoids trecking to the apartment, which may be on the fifteenth or eighteenth floor of a multi-story apartment building, only to learn that the tenant/customer desires some unusual dairy product which is not normally carried by the deliveryman, but is inventoried in his truck.

in designing an intercommunication system, a number of factors must be considered if the ultimate cost of the system is to be kept within the reasonable bounds necessary for commercial acceptance. Illustrative of such factors is the complexity of the remote station unit. If the remote unit is unnecessarily complex, the total cost of the system may be excessive, it being realized any excess in cost of a remote unit due to unnecessary complexity is multiplied by the number of units, apartments, offices, or the like in the building. For example, if in a 200-unit apartment building the remote unit requires an unnecessary relay, the cost added to the system is not just the cost of one relay, but rather 200 relays since there are two hundred apartments in the building. Due to this multiplication factor, it is therefore essential that the complexity of the remote unit be kept low if system cost is to be minimized.

Another important factor cost-wise is the number of individual wires which are required to interconnect the central station with the various remote units. If multiple independent wires are required between the central station and each remote unit, the total number of independent wires in the system becomes excessively large, the excessiveness being influenced by the multiplication factor noted above, namely, the number of apartments or offices in the building. Excessive wiring is costly for two reasons, namely, the wire itself is expensive as is the electrician s labor required to install it.

Another, and equally important, factor in the commercial acceptance of an intercommunication system is its convenience and ease of use by the tenant. Such systems should have remote units with a minimum number of controls, which controls are also easily understood and used. It must be remembered that the average user is often a woman who does not have a high level of mechanical aptitude or familiarity with technical subject matter.

It has been an objective of this invention to provide a two-way intercommunication system for apartments, office buildings, and the like which is relatively simple and inexpensive in design, and which can be conveniently used by mechanically unskilled personnel. This objective has been accomplished in accordance with certain principles of this invention by providing a system in which all stations, both central and remote, have a two-way speaker and are connectable in parallel to a pair of common audio lines, and a single common control line. In addition to the two audio lines and the single control line which are common to all stations, a plurality of wires corresponding in number to the number of remote units connect the central station with individual ones of the remote stations. At the central station an audio amplifier is provided in combination with amplification direction reverser which is responsive to the control line for reversing, under the control of the remote stations, the connection of the amplifier in the audio lines to thereby facilitate, on an alternate basis, communications to and from the remote stations. Also at the central station is a signal generator, such as an audio frequency tone generator, and a plurality of call switches corresponding in number to the number of remote units. The call switches selectively interconnect the output of the tone generator to the remote units via the individual remote unit signal lines. At the remote station, in addition to the two-way speaker, are four'state or condition switches. in the first, or standby, condition the switch means connects the remote speaker between its respective signal line and the common control line to facilitate initiation of an audible signal at a called remote station in response to actuation in the lobby of that stations call switch In a second condition of the remote station switch means, termed the talk condition, the remote speaker is connected across the audio lines to facilitate communication from the remote station to the central station via the audio lines and the amplifier which is normally connected to amplify communications originating at the called station. In the third, or listening, condition of the remote switch means, the remote station speaker is connected across the audio lines and additionally .a control signal. is

placed on the control and one audio line to actuate the amplification direction reverser to reverse the amplifier connections and permit amplification of signals originating at the central station. In the fourth condition of the remote station signal means a second control signal is placed on the control and one audio line to actuate a door unlocking mechanism at the central station, providing the remote station has first been called by the central unit. In this remote switch condition, the remote station speaker is disconnected from the audio lines.

The system of this invention has a number of novel and unobvious features. For example, by virtue of using a control line and audio lines which are common to each station, remote and central, the number of independent wires required is kept to a minimum regardless of the number of remote units in the system. In fact, the number of independent wires for a building having n remote stations is equal to n+3. Also, since the remote station requires only a two-way speaker and switch means, the materials cost of the system, which is directly related to the cost of a single remote unit by the number of units in the building, is kept to a minimum. Finally, since the remote unit switch means in the standby or normal condition connects the speaker to the signal line, a call can be initiated from the lobby without any required cooperation or participation by the party being called.

These and other advantages and objectives will become more readily apparent from a detailed description of the invention taken in conjunction with the drawings in which:

FIG. 1 is a schematic circuit in block diagram format of a preferred embodiment of an intercommunication system incorporating the principles of this invention;

FIGS. 2A-2C combined is a detailed circuit diagram ofthe preferred embodiment of FIG. 1.

With reference to FIG. 1, the preferred embodiment is seen to include a plurality of identical remote stations or units -1, 10-2, 10-n, and a central station or unit 12 to which each ofthe remote units 10-1, 10-2, 10-n can be selectively interconnected for two-way communication. The remote units 10-1, 10-2, 10-n preferably are located in different apartments or offices of a multi-apartment or multioffice building, while the central unit 12 is located in the lobby or other common area of the building. In the preferred embodiment the central unit 12 includes two identical stations 16 and 16' each of which has a two-

way speaker

17, 17, a door unlocking mechanism 18, 18', a call panel 19, 19', and a use lamp 9, 9'. The speakers l7, 17 of the stations 16, 16' can be selectively interconnected for twoway communication with similar two-way speakers, to

be described, in the remote units 10-1, 10-2, l0n.,

The door unlocking mechanisms 18, 18 of

stations

16, 16 are associated with normally locked doorswhich are designed'to be under the control of door switches,

to be described, associated with each remote unit 10-1, 10-2, 10 -n. The

call panels

19, 19 facilitate selec--=, tive signaling from thestations 16, 16' to the various remote units l0-l, l0-2, 10- n for the purpose of initiating a communication between one of the

central stations

16 or 16 and a selected remote unit. For this purpose, each of the call panels 19, 19' includes a plurality of. switches20-l, 20-2, 20-n and 20-1', 20-2, 20-n', respectively, corresponding in number to the number of remote units 10-1, 10-2, 10-n, and which when activated, result in the production at the corresponding remote unit of an appropriate signal such as an audible tone. The use lamp 9 of central station 16 becomes illuminated when central station 16' is in use. Likewise, lamp 9' signals when station 16 is in use.

In accordance with a preferred form, the identical

central stations

16 and 16 are located in the rear lobby and front lobby, respectively, of the building in which the remote units 10-1, 10-2, l0-n are located. In such case, the door unlocking mechanisms 18 and 18' control normaliy locked doors between the rear and front lobbies, respectively, and the interior of the building wherein the remote units 10-1, 10-2, 10-n are located.

The central station 12, in addition to the rear and front lobby stations 16 and 16', also includes an amplifier 22, a reversal switch 23, a lobby speaker selector switch 8, an audio tone signal generator 24, and a control circuit 25. The amplifier, reversal switch, selector switch, signal generator and control circuit may be physically located in either the front or rear lobby, or elsewhere in the building. The amplifier 22 provides amplification of two-way communications between the rear and front lobby speakers 17 and 17', respectively, and the speakers of the remote stations 10-1, 10-2, 10-n. The reversal switch 23 controls the amplification direction, that is, whether communications from, or to, the central station are amplified. The selector switch 8 selects the appropriate one of the lobby speakers, front lobby speaker 17' or rear lobby speaker 17, for connection to the amplifier 22 via the reversal switch 23, depending upon whether the called party is being called from the front orrear lobby station 16' or 16, respectively. The signal generator 24 generates an audio frequency tone which can be transmitted to one or more of the remote units 10-1, 10-2, l0-n under the control of the switches 20-1, 20-2, 20-n and 20-1', 20-2, 20-n' of the respective call panels 19 and 19'. The control circuit 25 includes the requisite circuitry, to be described in detail, for facilitating the signaling, communicating, door-unlocking, and other control functions of the system.

The remote units 10-1, 10-2, .10-n, which as indicated are structurally and operationally identical, each include a two-way speaker 26, a two-position manually operated door switch 28, a two-position manually operated talk switch 30, and a two-position manually operated listen switch 32. The remote speaker 26 facilitates two-way communication between its respective remote unit 10-1, 10-2, l0-n and the rear or front lobby speaker 17, 17'. The door switch 28 facilitates control from its respective remote unit 10-1, 10-2, l0-n of the rear and front door unlocking mechanisms 18, 18', facilitating unlocking by personnel at the remote units of the doors in the front and rear lobbieswhich permit access to the interior of the building in which the remote units are located. The door operated, either front or rear, by switch 28 depends upon whether the calling party is in the front or rear lobby= 16 or 16, respectively. The talk and listen

switches

30 and 32 permit personnel at the remote units -1, 10-2, 10-n to control the central station reversal switch 23 and thereby select the direction of permissible communication between the rear or front lobby speakers 17, 17', depending upon which is in use, and the remote speakers 26. When talk switch 30 is activated, the central station amplifier 22 amplifies speech from the remote unit 10 to the central unit 12, and when listen switch 32 is activated, the amplifier 22 amplifies speech from the central unit 12 to the remote unit 10. The talk and listen

switches

30 and 32 each have a normal, or standby, position in which they collectively connect the remote speaker 26 in a manner such that it will audibly reproduce a tone signal generated by the tone signal generator 24 should the remote unit be signalled from one or the other of the lobby call panels 19, 19'.

interconnecting the central station 12 and the remote units 10-1, 10-2, 10-n are two audio lines A1 and A2. Audio lines Al and A2 are common to each remote unit 10-1, 10-2, l0-n and alternatively to each of the

lobby units

16 and 16. Stated differently, the remote units 10-1, 10-2, 10-n and, alternatively, the rear and front lobby units 16 and 16', are connected in parallel to the audio lines Al and A2. The amplifier 22 is connected in audio lines A1 and A2 via the reversal switch 23, and, depending on which one of the talk or listen

switches

30 and 32 of a remote unit 10-1, 10-2, 10-n is activated, amplifies speech to or from the central station 12, respectively. The selector switch 8, also connected in audio lines A1 and A2, is located between the reversal switch 23 and the front and rear lobby speakers 17' and 17, and functions to connect, under control of circuit 25 as shown by line 7, the amplifier 22 (via reversal switch 23) to either the front or rear lobby speaker depending upon which lobby unit 16 or 16' is in use.

Also interconnecting the remote units 10-1, 10-2, 10-n is a control line C. The control line C, like the audio lines A1 and A2, is common to each of the remote units 10-1, 10-2, 10-n. Control line C is also connected to the control circuit 25. Thus, the remote units 10-1, 10-2, 10-n and the control circuit 25 connect in parallel to the control line C. The control line is responsive to the position of the remote unit talk and listen

switches

30, 32 for controlling via control circuit 25 the condition of the reversal switch 23 and, hence, the direction of speech amplifier 22. Control line C is also responsive to the door switch 28 for operating, via control circuit 25, the door locking mechanisms 18 and 18.

In addition to the audio lines Al and A2 and the control line C, there are n signal lines S1, S2, Sn. The signal lines S1, S2, Sn are respectively unique to the remote units 10-1, 10-2, 10-n, that is, each remote unit has its own individual signal line. Each signal line 81, S2, Sn is connected to the tone signal generator 24 via its respectively associated front lobby call panel switch -1', 20-2, 20-n and its respectively associated rear lobby call panel switch 20-1, 20-2, 20-n by lines S and S, respectively. With the signal lines S1, S2, Sn so connected, the audible tone generated by generator 24 can be selectively transmitted to any one of the remote units 10-1, 10-2, 10-n by activation of the respectively associated front lobby call panel switches 20-1', 20-2', 20n', or the respectively associated rear lobby call panel switch 20-1, 20-2, 20-n.

In operation, when a party in the front or rear lobby, herein termed the calling party desires to communicate with personnel at one of the remote units 10-1, 10-2, 10-n, herein termed the called party", the individual in the lobby activates the switch 20-1, 20-2, 20-n corresponding to the desired remote unit, if in the rear lobby, or the switch 20-1', 20-2', 20-n' if in the front lobby. For example, if the calling party in the front lobby wishes to communicate with remote unit 10-1, the calling party depresses switch 20-1 of front lobby call panel 19. Depression of this switch interconnects the tone signal generator 24 and signal line S1 of remote unit 10-1, in turn causing an audio signal to be transmitted to speaker 26 of remote unit 10-1. Since talk and listen

switches

30 and 32 of remote unit 10-1 are in their standby positions, speaker 26 of remote unit 10- 1 is connected between switch line S1 on which the audio signal is transmitted and control line C, and the tone is audibly reproduced by speaker 26 of called party unit 10-1. An audible signal is not reproduced by speakers 26 of the other remote units 10-2, 10-n, notwithstanding that they are connected between the control line C and their signal lines S2, Sn through their talk and listen

switches

30 and 32 which are in standby position, because the lobby call switches 20-2, 20-2', 20-n, 20-n' associated with these remote units have not been activated by the calling party to connect the signal generator 24 to their respective signal lines S2, Sn.

Activation of a call switch, e.g., switch 20-1 of the rear lobby, in addition to causing production of an audible signal at the called remote unit 10-1, also functions to cause the control circuit 25 to operate the selector switch 8 via line 7 to connect the appropriate lobby speaker, in this case rear speaker 17, to the amplifier 22 via reversal switch 23.

The audible signal produced by speaker 26 of called remote unit 10-1 signals personnel at this remote unit that a caller is in either the front or

rear lobby station

16, 16. At this point, since the talk and listen

switches

30 and 32 of called remote unit 10-1 are in the standby position, the remote speaker 26 of unit 10-1 is not connected to the common audio lines Al and A2 and the calling party in the front lobby unit 16' is unable to hear conversation originating in called remote unit 10-1. If the called party in remote unit 10-1 desires to speak with the calling party in front lobby station 16', the called party places talk switch 30 in the operative, or talk, position. With talk switch 30 in the talk position, remote speaker 26 is disconnected from signal line S1 and control line C instead is connected across the audio lines Al and A2. Additionally, control line C is open-circuited when the talk switch 30 is in the talk position. This is sensed by control circuit 25 to cause reversal switch 23 to connect the amplifier 22 such that its input is connected to the remote speaker 26 via lines A1 and A2 and its output is connected to the rear or

front lobby speakers

17, 17, as the case may be, depending upon where the calling party is located.

When the called party in remote unit 10-1 desires to stop talking, and start listening in anticipation of hearing conversation originated by the calling party in the lobby, the talk switch 30 is de-activated and returned to its standby position, and the listen switch 32 placed in the listen position. With the listen switch 32 in this position, the remote speaker 26 is connected to the audio lines A1 and A2. Additionally, a predetermined impedance is placed across control line C and audio line A2 which is sensed by the control circuit 25 to modify via line 2 7 the reversal switch 23 and in turn switch the input of the amplifier 22 to the central station speakers 17, 17' selected by switch 8 and theamplifier output to the remote speaker 26. The calling party in the front or rear lobby, as the case may be, is now free to speak into the

speaker

17 or 17, which speech is then amplified by amplifier 22 and transmitted to the remote unit -1 via lines A1 and A2 where it is transduced by speaker 26, which because switch 32 has been placed in the listen position, is connected to audio lines A1 and A2.

When the called party again wishes to talk, listen switch 32 is de-activated and talk switch 30 is placed in the talk position. With talk switch 30 in the talk position, the remote speaker 26 is connected to audio lines Al and A2 and the predetermined impedance associated with the talk switch position, e.g., an open circuit, is placed across control line C and audio line A2 with the result that the control circuit 25 causes, via line 27, the reversal switch 23 to reverse the input and output of the amplifier 22 to facilitate amplification of speech from the remote unit and transmission thereof to the central station 12.

Should the called party in remote unit 10-1 desire to unlock the door connecting the lobby, either from or rear, whereat the calling party is located, and the interior of the building in which the remote unit 10-1 is located, the door unlock switch 28 is switched from a normal or standby position to the active position. This is effective to place a predetermined impedance across control line C and audio line A2, in turn causing the control circuit 25 to generate a signal on either line 29' or 29 which activates the door unlocking mechanism 18 or 18 of the front or rear lobby, depending on where the calling party is located, to unlock that door.

When the called party desires to terminate all conversation, the talk and listen

switches

30 and 32 are placed in their standby positions which remove speaker 26 from audio lines A1 and A2. This prevents the calling party from either listening to conversation originating at the called station, or from speaking to the called station.

The remote units 10-1, 10-2, 10-n are each structurally and operationally identical, and therefore only remote unit 10-1 is described in detail. As can best be seen in FIG. 2, the unit 10-1 includes the twoway speaker 26 which, when spoken into, transduces the speech to an electrical signal on its output lines 26-] and 26-2 for transmission via audio lines Al and A2 to the central unit 12. The two-way speaker 26, when input with a speech-carrying electrical signal on lines 26-1 and 26-2 from the central unit 12 via audio lines Al and A2, transduces the speech signal to an audible output. Two-way speakers of the foregoing type are of conventional and well-known construction, and hence are not described in detail herein. Suitable two-way speakers are commercially available from Nu- Tone Division, Scovill Mfg. Co., designated Model 36548.

The two-way speaker 26 of unit 10-1 is alternately connectable between signal line S1 and control line C, and between audio lines A1 and A2 via the talk and listen

switches

30 and 32. The switch 30 has a first set of stationary, contacts 51-53 and a second set of stationary contacts 54-56. Cooperating with stationary contacts 51-53 is a translatable conductive segment 57, while associated with stationary contacts 54-56 is a translatable conductive segment 58.

Segments

57 and 58 are ganged, and normally biased by a spring (not shown) to the standby position shown.

Contacts

57 and 58 are movable to an active, or talk, position shown in phantom lines.

Listen switch 32 has three sets of stationary contacts 59-61, 62-64, and 65-67 which cooperate with translatable

conductive segments

68, 69 and 70, respectively.

Segments

68, 69 and 70 are ganged, and normally biased by a spring (not shown) to the standby position shown. Contact

segments

68, 69 and 70 are movable to an active, or listen, position shown in phantom lines.

With talk and listen

switches

30 and 32 in the standby positions shown,

contacts

51 and 52, 54 and 55, 59 and 60, and 62 and 63 are bridged by

segments

57, 58, 68 and 69, respectively. With these contacts bridged, lines 26-1 and 26-2 of two-way speaker 26 are connected across signal line S1 and control'line C. With speaker 26 connected across signal line S1 and control line C, a tone from the tone signal generator 24 can be transmitted to the speaker 26 of remote unit 10-1 if either the rear lobby panel switch 20-1 or the front lobby panel switch 20-1' is activated by a calling party seeking to initiate a communication with remote unit 10-1. Since remote units 10-2, 10-n are connected in parallel with remote unit 10-1 to control line C and individually to their respective signal lines S2 Sn, the speakers 26 of remote unit 10-2, 10-n are, when their

respective switches

30 and 32 are in the standby position, connected to the tone signal generator 24 via line C and their respective signal lines S2, Sn such that a tone can be transmitted to the remote unit 10-2, l0-n upon activation of the front or rear lobby switches 20-2, 20-2', 20-n, 20-n, respectively.

When talk and listen

switches

30 and 32 are in their standby position, audio lines A1 and A2 are open-circuited at the remote unit.

The talk switch 30, in addition to the standby position described above, also has a talk position. In the talk position,

segments

57 and 58 are translated to the phantom line position such that contacts 52 and 53 are bridged by conductive segment 57 while contacts 55 and 56 are bridged by conductive segment 58. With these contacts bridged, speaker lines 26-] and 26-2 of speaker 26 in remote unit 10-] are connected to audio lines Al and A2, respectively. Lines A1 and A2 are in turn connected to the input of amplifier 22 via untransferred contacts CRI-A and CRl-B of a control relay CR1 to be described, relay contacts CRl-A and CRl-B forming part of the reverser switch 23. The output of the amplifier 22 is connected to the selector switch 8 via untransferred relay contacts CRl-C and CRl-D, respectively, of relay CR1, contacts CRl-C and CRl-D also forming part of the reverser switch 23. The selector switch 8, in turn, alternately connects the output of the amplifier 22 to either the front or rear lobby speaker 17' or 17, depending upon whether the calling party is in the front or rear lobby. With talk switch 30 of unit 10-1 in the talk position, lines S1 and C are open-circuited.

Thus, with the talk switch 30 of remote unit 10-1 in the talk position, speaker 26 of remote unit 10-1 is connected via audio lines Al and A2 and the reverser switch 23 to the input of the amplifier 22; while either the front or rear lobby speaker 17', 17 is connected to the output of the amplifier 22 via switch reverser 23 and selector switch 8, thereby establishing an audio path from the speaker of remote unit 10-1 through the amplifier 22 to the rear or

front lobby speakers

17 and 17 depending on the location of the calling party. The speakers 26 of remote unit 10-2, l-n, as long as their respective talk switches 30 are in the standby position, are not connected to the input of amplifier 22 via audio lines A1 and A2 and the reverser switch 23. Accordingly, only speech input to speaker 26 of remote unit -1, whose talk switch 30 is in the talk position, will be transmitted to the input of the amplifier and following amplification therein to the front or rear lobby speakers 17' and 17.

The listen switch 32 of remote unit 10-1, in addition to its standby position, also has a listen position. In the listen position,

conductive segments

68, 69 and 70 are translated to the phantom line position. With these conductive segments so positioned, stationary contacts 60 and 61 are bridged by segment 68; contacts 63 and 64 are bridged by conductive segment 69; and contacts 66 and 67 are bridged by conductive segment 70. Contact 59 which connects to signal line S1 is not bridged to another contact. With contact 59 not bridges, line 81 is open-circuited. The bridging of contacts 60, 61 by segment 68, and bridging of contacts 63'and 64 by segment 69 connects speaker lines 26-1 and 26-2 of speaker 26 of remote unit 10-1 to audio lines Al and A2, respectively. The bridging of contacts 66 and 67 by segment 70 connects a predetermined impedance R48 between control line C and audio line A2. The presence of impedance R48 across lines C and A2 is effective to energize control circuit relay CR-l, in a manner to be described, transferring relay contacts CRl-A to CRl-D of reverser switch 23 from the position shown.. With the relay contacts CRl-A to CRl-D transferred, the speaker 26 of remote unit 10-1, which is connected to lines A1 and A2 via switch 30 when in its listen position, is connected to the output of amplifier 22 while either the front or rear lobby speakers l7, 17 is connected to the input of amplifier 22 via selector switch 8. Thus, the placement of impedance R48 across control line C and audio line A2, when the switch 32 of remote unit 141-] is in the listen position, is effective to energize relay CR1 and transfer the contacts CRl-A to CRl-D of reverser switch 23, thereby effectively connecting the appropriate lobby speaker 17, 17' to the input of amplifier 22 via selector switch 8 and speaker 26 of remote unit 10-1 to the output of amplifier 22.

Switches

30 and 32 of remote units 10-2, 10-n function in a manner similar to that of

switches

30 and 32 of unit 10-1.

The door control switch 28 of remote unit 10-1 includes a conductive contact 28-1 movable between an inactive or standby position (shown in FIG. 2) and an active position shown in phantom lines in which it bridges stationary contacts 28-2 and 28-3. in the active position of door control switch 28, a predetermined impedance R49 is connected across control line C and audio line A2. This impedance R49 across lines C and A2 is sensed by the control circuit 25 and, in a manner to be described, operates the front or rear door unlocking mechanism 18 or 18, depending upon whether the calling party is at the front or

rear lobby

16 or 16, respectively.

Door switches 28 of remote units 10-2, 10-n, like door switch 28 of remote unit 10-1, unlocks the appropriate front or rear lobby door when placed in the active, or door unlock position, shown in phantom lines.

The audio tone signal generator 24 and control circuit 25 are described presently in conjunction with a detailed description of the operation of the system of this invention in its various modes. When a call switch 20-1 20-n in the front lobby 16 or 20-1 20-n in the rear lobby 16, for example, switch 20-1 of the rear lobby 16, is activated, a circuit is completed from the positive bus which is preferably at +24 volts to the ground bus via resistor R28, resistor R46, control line C, speaker 26 of called remote unit 10-1, signal line S1, activated call switch 20-1, signal line S, resistor R38, and resistor R31. Completion of this circuit causes current to flow through resistor R31 raising the potential of the base of a transistor TR16, rendering this normally nonconducting transistor in a conductive state. Conduction of transistor TR16 causes a flow of current in its emitter-collector path which includes resistors R11 and R12 connected between the collector of transistor TR16 and the positive bus.

Current flow through resistor R11 applies a signal to the base of a transistor TR9 rendering this transistor which is normally nonconductive in a conductive state. Conduction of transistor TR9 causes current to flow fiow through its emitter-collector path to a tone signal generator circuit 24 which includes a unijunction transistor TR2, a capacitor C 1, and charging resistors R39 and R15. The flow of current through conducting transistor TR9 causes the tone generator 24 to produce an audio frequency signal at its output line 100. The audio frequency signal present on line is resistively coupled to a tone signal generator amplifier including transistors TRl and TR17, providing on line 102 an amplified audio frequency tone signal.

The conduction of transistor TR16 in response to closure of call switch 20-1 is also effective to switch normally nonconducting transistor TR8 to a conductive state. The conduction of transistor TR8 short-circuits resistor R28 which was in series with the speaker 26 of remote unit 10-1 via lines C and S1, permitting a maximum level of audio frequency tone signal to flow through the speaker 26 of remote unit 10-1 when the amplified output of the tone generator 24 present on line 102 is coupled to common signal line S in a manner to be described.

Completion of the circuit from the positive bus through resistors R28, R46, line C, speaker 26 of remote unit 10-1, line S1, line S, and resistors R38 and R31, to ground bus as a consequence of closing call switch 20-1 is also effective to bias via diode D23 the base of transistor TR12, rendering this normally nonconductive transistor in a conductive state. Transistor TR12 is in series with a control relay CR2 associated with the rear lobby l6, and when turned on renders control relay CR2 energized via a path which includes a contact CR3-A of a control relay CR3, to be described, which is associated with the front lobby 16. Contact CR3-A of relay CR3 associated with the front lobby is in the position shown permitting relay CR2 associated with the rear lobby to be energized in response to closure of a rear lobby call switch, such as call switch 20-1, when a call switch in the front lobby has not been previously energized. Contact CR3-A, therefore, is a lock-out contact in the sense that it prevents control relay CR2 associated with the rear lobby from being energized if control relay CR3 associated with the front lobby is energized by virtue of the prior actuation of a front lobby call switch 20-1 20-n'. Energization of relay CR2 which, as indicated, is associated with the rear lobby, transfers its own contact CR2-D from the position shown, connecting the positive bus to the base circuit of a transistor TR13, energizing normally nonconducting transistor TR13.

Transistor TR13 is in parallel with transistor TR12 and provides an alternate energization path for ener gized relay CR2. Thus, transferred contact CR2D in connection with transistor TR13 whose emitter-collector path is in series with relay CR2, function as a latching circuit for relay CR2. The transfer of relay contact CR2-D from the position shown also performs two other functions. First, it applies potential from the positive bus via a diode D and a line 105 to an astable multi-vibrator 106 which includes transistors TRS and TR6 cross-coupled in a well-known manner to produce at its output terminal 107 a square-wave, preferably of .relatively low frequency such as two cycles per second. The two cycle per second output at astable multi-vibrator terminal 107 switches a transistor TR7 at the same frequency. Transistor TR7 has its emitter-collector path connected between the ground bus and the front and rear

lobby use lamps

9 and 9, causing whichever of these lamps having its positive side connected to the positive bus 24 to be operated in a flashing mode. In this example, wherein a call switch -1 in the rear lobby 16 is activated to energize control relay CR2, in turn transferring contact CR2-D from the position shown, no connection exists between the positive bus and the positive side of the rear lobby use lamp 9. The use lamp'9 therefore will not operate in a flashing mode in response to the intermittent grounding of the negative side of the lamp by multi-vibrator-driven transistor TR7. However, the positive side of the front lobby use lamp 9 is connected to the positive bus by diode D22 and the untransferred contact CR3-A of relay CR3 associated with the front lobby which is not energized since a front lobby call switch 20-1, 20-n has not been activated. Hence, the intermittent grounding of the low voltage side of front lobby use lamp 9' by transistor TR7 is effective to flash the front lobby use lamp at the frequency of the multi-vibrator 106, indicating to prospective users of the front lobby call panel that the system is in use.

The energization of relay CR2 and the transfer of contact CR2-D in response to actuation of a rear lobby call switch 20-1 also connects the positive bus via diode D10 to a timing circuit 110 which includes a unijunction transistor TR3, a capacitor C2, and charging resistors R40 and R17. The connection of the positive bus to the timing circuit causes the capacitor C2 -to intimate charging. When the capacitor C2 charges to a potential sufficient to fire the unijunction transistor TR3, the capacitor C2 discharges through the fired unijunction transistor TR3 and a resistor R19 producing a negative pulse on line 111. The negative pulse on line 111, in a manner to be described, functions to reset certain portions of the control circuitry if there is no answer from the called station 10-1 within a predetermined time interval determined by the time constant of the timer 1 10.

Energization of relay CR2 associated with the rear lobby in response to actuation of rear lobby call switch 20-1 also functions to transfer contacts CR2-A and CR2-B which constitute the selector switch 8, connecting the rear lobby speaker to the amplifier 22 via the reversal switch 23. Contact CR2-C of energized relay CR2 also transfers to apply the amplified audio frequency tone output on line 102 to common signal line S and in turn via activated call panel switch 20-] to line 81. Since line S1 is unique to remote unit 10-1 associated with activated call switch 20-1, the amplified audio frequency tone is transmitted to remote unit 10-1 and only to this remote unit, causing the speaker 26 at this remote unit to produce an audible tone summoning the called party.

The amplified tone present on line 102 is also applied via capacitor C7 to the input of central unit amplifier unit 22 which after amplification applies the tone signal to the rear lobby speaker 17 via the reversal switch 23 which is normally connected such that the output of the lobby amplifier 22 is input to the selector switch 8,-

which in turn is input to the selected lobby speaker, in this case rear speaker 17. Thus, in response to activation of rear lobby call switch 20-1, an audible tone is transmitted to the speaker of called remote unit 10-1, as well as to the rear lobby speaker 17. This tone transmission to the called unit and the lobby whereat the calling party is located continues as long as the call switch 20-1 is activated.

When the call switch 20-1 is de-actuated, or released, the path is interrupted from the positive bus to ground via resistor R28 which is short-circuited by conducting transistor TR8, resistor R46, line C, speaker 26 of remote unit 10-1, line S1, line S, and resistors R38 and R31. Interruption of this circuit turns transistor TR16 off, which in turn turns off transistors TR8 and TR9. Transistor TR9 turns off the tone generator 24, while transistor TR8 removes the shortcircuit from resistor R28. Interruption of the above described path by release of call switch 20-1 also turns off transistor TR12. However, transistor TR13 remains conducting by virtue of the application to its base circuit of a positive bias from the positive bus provided by transferred contact CR2-D of energized relay CR2, which relay was energized resulting in the conduction of transistor TR13 and the latching of relay CR2 when transistor TR12 was initially energized by activation of call switch 20-1.

If there is no answer from the called remote unit 10-1, that is, if neither the talk nor the listen switches 30 or 32 is activated, the timer circuit 110 eventually produces a negative reset signal on line 111 to switch transistor TR13 off, in turn de-energizing relay CR2 which deactivates the flashing multi-vibrator 106 causing flashing front use lamp 9' to extinguish, and disconnects the rear speaker 17 via selector switch 8 from the amplifier 22. Specifically, the negative signal produced on line 111 from the timer circuit 110 in response to discharging of capacitor C2 via fired unijunction transistor TR3 applies a negative bias to the base of conducting transistor TR13 via capacitor C5, causing this transistor to be rendered nonconductive. With transistor TR13 off, relay CR2 is de-energized, transistor TR12 the alternative energization path for relay CR2 having been rendered nonconductive when the call switch 20-1 was released. De-energization of relay CR2 transfers its contacts CR2-A and CR2-B of selector switch 8 to the position shown, disconnecting the rear speaker 17 from the amplifier 22. Additionally, relay contact CR2-D transfers to the position shown, removing a connection from the positive bus to the flashing multi-vibrator 106 causing this circuit to cease switching of transistor TR7 and in turn the intermittent grounding of the ground sides of front and rear use lamps 9' and 9. Front use lamp 9', the lamp which when relay CR2 was energized had its positive side connected to the positive bus via diode D22 and non-transferred contact CR3-A associated with front lobby relay CR3, ceases to be operated in the flashing mode as a consequence of the termination of the flashing operation of multi-vibrator 106. Transfer of contact CR2-D to the position shown in response to reset of relay CR2 by the timer 110 also removes the connection from the positive bus to the timer circuit 110 provided by diodes D10 and resistors R40 and R17. Hence, timer capacitor C2 does not begin charging to initiate a new timing cycle. Finally, de-energization of relay CR2 transfers contact CR2C to the position shown, interrupting the circuit between common signal line S and the amplified output of the tone generator on line. 102.

As noted previously, a person in the rear lobby 16 desiring to communicate with remote unit 10-1 initiates a communication by actuating call panel switch 20-1. This, in a manner described in detail earlier, transmits a tone to the speaker of called remote unit 10-1 so long as the call switch 20-1 is activated. Additionally, activation of the call switch 20-1 causes relay CR2 associated with the rear lobby to latch. With rear lobby control relay CR2 latched, flasher circuit 106 is energized via transferred contact CR2-D and front lobby use lamp 9 operated in an intermittent flashing mode via untra'nsferred contact CR3-A associated with front lobby control relay CR3. Additionally, timer circuit 110 is energized via transferred contact CR2-D and the rear lobby speaker 17 is connected via transferred contacts CR2-A and CR2-B to the reversal switch 23. The reversal switch 23, as will be described later, is in its normal condition in which rear speaker 17 is connected to the output of the amplifier 22 and audio lines A1 and A2 are connected to the input of the amplifier 22. Assuming the call switch 20-1 has been released, transistors TR12 and TR16 are nonconductive as are transistors TR8 and TR9, and tone generator transistor TRZ. Relay CR2, however, is latched ON via a conducting transistor TR 13, which is biased to a conduction state by transferred contact CR2-D of latched relay CR2.

With the system in the condition outlined above, if the personnel at called remote unit 10-1 desire to speak to the calling party in the rear lobby, the called party activates the talk switch 30, moving it from the position shown in solid lines to the position shown in phantom lines. Activation of the talk switch 30 moves the speaker 26 of the called unit 10-1 from across control line C and signal line S1 and places the speaker across audio lines A1 and A2. Since the normal condition of reversal switch 23 is such that audio lines A1 and A2 are connected to the input of amplifier 22, and the speaker, in this case rear lobby speaker 17, selected by selector switch 8 is connected to the output of amplifier 22, the called party upon actuation of the talk switch 30 is now in a position to communicate with the calling party in the rear lobby 16. The voice communication from the called party will be audibly reproduced by the rear lobby speaker 17. The voice communication will not, however, be reproduced by speaker 17 in the front lobby 16 since front lobby speaker 17' is not connected to the output of the amplifier by the selector switch 8.

Further, the voice communication from the called unit 10-1 cannot be received by any other remote units. Specifically if another remote unit 10-2, 10-n were to have its talk switch 30 activated, the speaker of that remote unit, like the remote speaker of called remote unit 10-1, would not be connected via audio lines A1 and A2 to the output of amplifier 22, and hence could not receive the voice communication from called unit 10-1. If a remote unit other than called unit 10-1 were to have its listen switch activated, it could not receive the communication from called unit 10-1, for reasons to become apparent later, because activation of the listen switch of the uncalled unit would be effective to switch the condition of the reversal switch 23 such that the speaker 26 of called unit 10-1 is not connected via audio lines Al and A2 to the input of amplifier 22. Therefore, even though activation of listen switch 32 at an uncalled remote unit is effective to switch the speaker of the uncalled remote unit to the output of amplifier 22, there is no voice communication being amplified by amplifier 22 to be received by the uncalled unit since speaker 26 of called unit 10-1 is no longer connected to the input of amplifier22 via audio lines A1 and A2.

If after talking to the rear lobby unit 16 the personnel at called unit 10-] desires to terminate the communication, the talk switch 30 thereat is released. This removes speaker 26 of called unit 10-1 from across audio lines A1 and A2 and returns the called unit to the normal or standby position with the speaker across signal line S1 and control line C. Rear lobby speaker 17 remains connected via transferred contacts CR2-A and CR2-B of selector switch 8 to the reversal switch 23 and hence to the output of the amplifier 22 until relay CR2 is de-energized by a reset signal on line 111 from the timing circuit in a manner described previously.

If after talking to the rear lobby unit 16, the personnel at called unit 10-1 desires to permit the calling party to speak, the called party activates the listen switch 32, placing the system in the listen mode. Of course, the listen switch 32 must be activated before the timer circuit 110 has reset the system, particularly de-energized relay CR2 by production of a negative reset signal on line 11 1. Assuming that the listen switch 32 at called unit -1 has been activated before the timer 110 has had an opportunity to produce the reset signal on line 111 to de-energize relay CR2, activation of the listen switch 32 will effectively place the system in the listen mode. Specifically, activation of the listen switch 32 at called unit 10-1 places the speaker 26 of that remote unit across audio lines Al and A2.

Additionally, activation of the listen switch places resistor R48 across control line C and audio line A2. Placement of resistor R48 across control line C and audio line A2 causes current to flow from the positive bus to ground via resistor R28, resistor R46, control line C, resistor R48, audio line A2, and the primary winding W1 of transformer T1. The effect of current flowing in this path causes the voltage of control line C to decrease which in turn places an increased voltage across zener diode D11 connected in the base circuit of a transistor TR15. The increased voltage drop across zener diode D11 is sufficient to cause this diode to break down, switching normally nonconducting transistor TRIS to a conductive state. Transistor TRIS has its emitter-collector path connected in series with a relay CR1 and when switched to a conductive state completes an energization path for relay CR1 through line 120, diode D4, line 121, and the emitter-collector path of conducting transistor TR13 which is maintained in a conductive state by transferred contact CR2-D of control relay CR2, which it will be recalled was energized when call switch 20-1 was activated to call remote unit 10-1. Relay CR1 remains energized only so long as the listen switch 32 is activated.

Energization of relay CR1 in response to activation of the listen switch 32 at called unit 10-1 is effective to transfer contacts CR1-A and CR1-B forming part of the reversal switch 23 to connect the rear lobby speaker via selector switch 8 to the input of amplifier 22. Additionally, contacts CR1-C and CR1-D, also forming part of the reversal switch 23, transfer from the position shown to connect audio lines A1 and A2 and, hence, remote speaker 26 of the remote unit 10-l to the output of amplifier 22. With rear lobby speaker17 connected to the input of amplifier 22 and the speaker 26 of remote unit 10-1 connected to the output of amplifier 22, the system is in the listen mode, permitting conversation to be transmitted from the rear lobby 16 to called unit 10-1. As noted, the system will remain in the listen mode so long as the listen switch is held in the active position shown in phantom lines.

Energization of relay CR1 in response to activation of the listen switch, in addition to reversing the condition of reversal switch 23 to connect the lobby and remote unit speakers to the input and output, respectively, of amplifier 22, also performs certain additional functions. Specifically, relay contact CR1-E transfers from the position shown to discharge timing capacitors C2 effectively resetting the timer. Since contact CR l-E remains transferred from the position shown so long as relay CR1 is energized by activation of the listen switch, the capacitor C2 remains short-circuited for the duration of the listen mode, preventing the timer 110 from beginning a timing cycle.

Relay contact CR1-F also transfers from the position shown to ground the low voltage side of relay CR1 via line and diodes D4 and D6. Thus, continued eneri gization of relay CR1 is no longer dependent upon continued conductivity of transistor TR13. Transferred contact CR1-F is also effective to ground via diode D6 control relay CR2 such that continued conductivity of latched relay CR2 is no longer dependent upon continued conduction of TR12. It is desirable that continued conduction of relay CR1 and CR2 not be dependent upon continued conduction of transistor TR13 since there is a tendency for this transistor to be rendered nonconductive when contact CR1-E transfers from the position shown and discharges timing capacitor C2. Specifically, when contact CR1-E transfers from the position shown and discharges timing capacitor C2, a negative signal is produced on timer output line 1 11 which has a tendency to terminate conduction of transistor TR13. Thus, relays CR1 and CR2 which, prior to transfer of contact CR1-F, depended for continued conductivity on the conduction of transistor TR13, would cease conducing were it not for transferred contact CR1-F which in effect short-circuits the low voltage side of relay CR1 and CR2 to ground independent of transistor TR 13.

When the called party at remote unit 10-1 desires to terminate the listen mode, that is, end conversation originating at the central unit, the listen switch 32 is deactivated and returned to the solid line position. This is effective to remove speaker 26 of remote unit 10-1 from across audio lines A1 and A2 and transfer the speaker to lines S1 and control line C. Additionally, resistor R48 is no longer connected between control line C and audio line A2, terminating the path from the positive bus to ground via resistors R28, R46, control line C, resistor R48, and primary winding S1 of transformer T1. With this conductor path terminated, the voltage across zener diode D11 decreases to a point wherein the diode is no longer in a breakdown condition and transistor TRIS is rendered nonconductive, in turn interrupting the energization path for relay CR1 causing this relay to become de-energized. Relay contacts CR1-A and CR1-B transfer to the position shown, disconnecting lobby speaker 17 from the input of amplifier 22 and connecting it to the output of amplifier 22. Contacts CR1-C and CR1-D return to the position shown transferring audio lines Al and A2 from the output of amplifier 22 to the input of amplifier 22. Contact CR1-E transfers to the position shown, removing the short-circuit from timing capacitor C2. With capacitor C2 no longer short-circuited, it is free to charge through transferred contact CR2-D, diode D10, and resistors R40 and R17. Contact CR1-F also transfers to the position shown. Relay CR2 which is now energized is connected to the ground bus via conducting transistor TR13 rather than via contact CR1-F, diode D6 and line 121. Thus, control of de-energization of conducting relay CR2 is now returned to transistor TR13.

When timing capacitor C2 has charged to a value sufficient to fire unijunction transistor TR3, a negative reset signal is produced on output line 111 which is capacitively coupled via capacitor C5 to the base of conducting transistor TR13, rendering this transistor nonconductive. Nonconduction of transistor TR13 interrupts'the energization circuit for relay CR2 causing this relay to become de-energized. De-energization of relay CR2 in the manner described previously disconnects the rear speaker 17 from the reversal switch 23 and hence from the amplifier 22; terminates operation of the flasher multi-vibrator 106 and hence extinguishes the front use lamp 9; terminates charging of the capacitor C2 via diode D10 and resistors R40 and R17; and disconnects the output of amplifier transistor TR17 from common signal line S.

Of course, prior to the production of the reset signal on line 111 from timer circuit 110 personnel at the called remote unit 10-1 can place the system in the talk mode by activating switch 30 to permit voice communication from the called unit to the rear lobby 16 in a manner described. Activation of the talk switch could then be followed by activation of the listen switch to place the system in the listen mode which, as noted, would have the effect of resetting the timer 110 and holding it in an inoperative condition until the listen switch is again de-activated.

If desired, and before relay CR2 is de-energized by a reset signal on line 111 from timer circuit 110, personnel at the called unit 10-1 may activate the rear door release mechanism 18. Specifically, the rear door release mechanism 18 is activated by actuating door release switch 28. This is effective to place resistor R49 between control line C and audio line A2 which completes a circuit from the positive bus through resistor R34, zener diode D1, resistor R36, control line C, resistor R49, audio line A2, and primary winding W1 of transformer T1. Completion of this circuit decreases the voltage of control line C, placing an increased voltage across zener diode D1, which is sufficient to break down this diode. Breakdown of zener diode D1 biases normally nonconducting transistor TR14 to a conductive state. Transistor TR 14 which has its emitter-collector path in series with a control relay CR4, when rendered conductive, causes relay CR4 to be energized via a path which includes diode D4, line 121, and the emitter-collector path of conducting transistor TR13. It will be recalled that transistor TR13 is biased to a conductive state when contact CR2-D transfers to the position shown upon energization of relay CR2 when call switch 20-1 is actuated.

Contact CR4B transfers from the position shown to complete an energization circuit from a power supply 125 to the rear door release mechanism 18 viauntransferred contact CR3D of control relay CR3 associated with the front lobby. Control relay CR3 is the front lobby counterpart of control relay CR2 and remains unenergized so long as a call switch 20-1 20-n in the front lobby is not activated. Thus, as long as the calling party is located in the rear lobby, relay contact CR3-D remains in the position shown to partially complete an energization circuit from the power supply 125 to the rear door release mechanism 18. When the door release switch 28 in the remote unit is activated to energize relay CR4, the partially completed circuit to the rear door release mechanism 18 via untransferred contact CR3-D is completed by the transfer of contact CR4B. Had the calling party been located in the front lobby, relay CR3 would be energized and contact CR3-D transferred from the position shown, such that when contact CR4-B transfers in response to energization of relay CR4 as a consequence of activating the door release switch 28, the front door release mechanism 18' would be activated instead of the rear door release mechanism 18.

Energization of relay CR4 also transfers contact CR4-A which completes a circuit from a positive bus to the relay CR4 to latch this relay independent of transistor TR14, the energization state of which is controlled by door release switch 28. Transfer of contact CR4- A also completes a second charging path for capacitor C2 via diode D12, resistor R18 and resistor R41. This second charging path is in addition to the path through diode D10, resistor R40 and resistor R17 established by transferred contact CR2-D. With two charge paths established for timer capacitor C2, the capacitor charges at an increased rate until eventually unijunction transistor TR3 fires and capacitor C2 discharges to produce a negative reset signal on line 111 output from timer circuit 110. The reset signalon line 111 is capacitively coupled via capacitor C5 to the base circuit of conducting transistor TR13, causing this transistor to switch off, in turn de-energizing relay CR2. De-energization of relay CR2 disconnects the rear lobby speaker 17 from the reversal switch 23 and, hence, the amplifier 22; interrupts the charging circuit for capacitor C2 via diodes D10 and resistors R40 and R17; interrupts the energization circuit for the flasher multi-vibrator 106, preventing flashing of the front use lamp 9'; and disconnects output line 102 of amplifier TR17 from common signal line S. Turning off of transistor TR13 in response to the reset signal on line 111 from timer circuit also interrupts the path to ground bus for relay CR4, causing relay CR4 to become tie-energized. De-energization of relay CR4 transfers contact CR4-B to the position shown, interrupting the energization circuit from source to the rear door release mechanism 18. Contact CR4-A also returns to the position shown interrupting the charge path for capacitor C2 via diodes D12 and resistors R18 and R41, as well as removing the latch circuit from the positive bus for relay CR4. The entire system is now reset.

If desired, the rear door unlocking mechanism 18 can be energized independently of the door release switches 28 located inremote units 10-1, 10-2, l0-n. For example, a manually operated switch may be provided which when activated, for example, with a key, completes a circuit from the positive bus to the ground bus via resistor R34, resistor R35, line 141, resistor R5, and resistor R6. Completion of this circuit switches normally nonconducting transistor TR12 to a conductive state, which in turn energizes relay CR2 through normally non-transferred contact CR3-A, resistor R45 and diode D15. Energization of relay CR2 transfers contact CR2-D to switch normally nonconducting transistor TR13 on. With transistor TR13 conducting, a latch circuit is established for relay CR2 independent of transistor TR12, the conductive state of which is responsive to, among other things, keyoperated switch 140. Transfer of contact CR2-D also establishes a charging path through diode D10, resistor R40 and resistor R17 for timing capacitor C2 of timing circuit 110. Actuation ofkey-operated switch 140 also biases normally nonconducting transistor TR14 to a conductive state, which in turn energizes relay CR4 via diode D4 and line 121 and conducting transistor TR13. Energization of relay CR4 transfers contact CR4-B to complete an energization circuit from the power supply 125 to the rear door release mechanism 18 via normally untransferred contact CR3-D. Additionally, relay contact CR4-A transfers to latch relay CR4 in a conductive state independent of transistor TR14, the conductive state of which is controlled by switch 140. Transfer of contact CR4-A also completes a second charging circuit for capacitor C2 through diode D12, resistor R18 and resistor R41. When timing capacitor C2 charges to a point sufficient to fire unijunction transistor TR3, a negative reset signal is produced on line 111 of timing circuit 110 which is coupled via capacitor C5 to the base of conducting transistor TR13, rendering this transistor nonconductive and in turn de-energizing relay CR2 and relay CR4, which rely on conduction of transistor TR13 for completion of a circuit to ground. De-energization of relay CR4 transfers contact CR4-B to the position shown de-energizing the rear door release mechanism 18. The entire circuit is now reset.

The foregoing description of the operation of the system assumes that a call switch in the rear lobby 16 was activated. Operation of the system if a call switch in the front lobby 16' is activated is the same as if the call switch in the rear lobby were activated with the following exceptions. Transistor TR switches ON instead of transistor TR12, with the result that relay CR3 is energized and not relay CR2. Additionally, transistor TR] 1 becomes energized to latch relay CR3 in an energized condition in much the same manner that transistor TR13 latched relay CR2 when a rear lobby call panel switch was activated; Energization of relay CR3 in response to activation of a front panel call switch transfers contact CR3-C from the position shown. Transfer of contact CR3-C connects the positive bus to the flasher multi-vibrator 106 which in turn intermittently via transistor TR7 connects the ground bus to the

use lamps

9 and 9. However, the transfer of contacts CR3-A interrupts the connection from the positive bus through diode D22 to the front use lamp 9' preventing this lamp from being flashed. Rear use lamp 9 is flashed by the intermittent grounding because its positive side is connected to the positive bus via diode D17 and untransferred contact CR2-D of relay CR2 which, as indicated, is not energized when a front panel call switch is activated. Transfer of contact CR3-C also connects the positive bus to the base of transistor TR] 1 to, as indicated previously, latch transistor TRll in a conductive state, in turn latching relay CR3 in an energized condition.

Transfer of contact CR3-A completes a charging circuit from the positive bus through charging resistors R40 and R17 to the timing capacitor C2 of timer circuit 110. This capacitor charging circuit functions in a manner similar to that described in connection with the previous discussion wherein relay CR2 is energized in response to actuation of a rear lobby call switch. Relay contact CR3-D transfers from the position shown to partially complete a circuit from the power supply 125 to the front door release mechanism 18'. With this partial circuit completed, when the door release switch 28 is actuated and relay CR4 energized, contact CR4-B transfers to complete an energization circuit to the front door release mechanism 18.

The front door speaker 17 is connected to the reversal switch 23 and, hence, to the amplifier 22 via nontransferred contacts CR2-A and CR2-B. Hence, the system is in condition for communication between the remote station and the speaker of the front lobby.

Resetting of the system in response to a reset signal on line 111 from the timer circuit when a front lobby call switch is activated is similar to that previously described in connection with activation of a rear panel call switch. However, the reset signal on line 1 l 1 is coupled via a capacitor C6 to the base circuit of transistor TRll turning this transistor off which in turn de-energizes relay CR3. De-energization of relay CR3 transfers contact CR3-C to the position shown, deenergizing the flashing circuit 106, enabling front lobby use lamp 9, and interrupting the charging path to the timing capacitor C2 via resistors R40 and R17.

Operation of the front door release mechanism 18 in response to activation of the door release switch 28 is similar when a front lobby call panel switch is operated to the operation when a rear call panel switch is operated. However, relay CR4 completes a circuit to ground via diode D3 and conducting transistor TR11 rather than diode D4, line 121 and conducting transistor TR13. This ground circuit for conducting relay CR4 is interrupted when transistor TRll is rendered nonconductive in response to a reset signal on line 111 coupled to the base of transistor TRll by capacitor C6. When the front lobby is being used and the listen switch of a remote unit is activated, relay CR1 completes a circuit to ground through transistor TRll rather than transistor TRIS. Finally, when the front lobby is being used, the amplified tone on line 102 is coupled to common signal line S via transferred contact CR3-B instead of contact CR2-C.

To reset the timer circuit 1 10 each time a call switch 20-1, 20-n or 20-1, 20-n' is activated, a transistor TR4 is provided having its emitter-collector path in parallel with timing capacitor C2 and its base connected to the output of the tone generator amplifier TRl7 on line 102. When a call switch is activated and an amplified tone present on line 102, transistor TR4 is rendered conductive causing capacitor C2 to discharge effectively resetting the timer 110. Thus, personnel at the remote units are permitted the full duration of the timer 110 to respond to a call.

Diode D16 connected between the collector of transistor TR14 and relay contact CR4-A prevents switching of transistor TR10 to a conductive state and in turn energization of relay CR3 to activate the rear door release 18 via contact CR4-B if the door release switch 28 of a remote unit 10-1, 10-n is activated when neither the front nor rear lobby is in use. Without diode D16, closure of a door release switch 28 in a remote unit 10-1, l0-n would switch transistor TR14 on, in turn switching transistor TR10 on to energize relay CR3 and complete a circuit to the rear door release mechanism 18 via tr'ansferredcontact CR3-D and transferred contact CR4-B. Contact CR4-B would have transferred upon energization of relay CR4 as a consequence of conduction of transistor TR14 when the door release switch 28 was activated.

Having described my invention, I claim:

1. An intercommunication system comprising n remote stations each having a two-way speaker,

a central station having a first two-way speaker,

first and second audio lines each connected to each of said n remote stations and connectable to said central station two-way speaker,

audio frequency signal generator means,

it signal lines each connected between said signal generator means and a different one of said n remote stations,

a first set of n call switches at said central station and associated with said first speaker, each of said switches corresponding to a different one of said n remote stations for transmitting an audio frequency signal between said signal generator means and a selected remote station via the signal line connected to the selected remote station,

a single common control line connected to each of said n remote stations and said central station,

audio frequency amplifier means connected in said audio lines,

amplifier control means connected to said amplifier and between said single control line and at least one of said audio lines, said control means responsive to a control signal on said control and at least one audio line from said remote stations for amplifying, on an alternative basis, communications on said audio lines in one direction from said remote stations and in another direction from said central station,

n switch means respectively at different ones of said remote stations, each of said switches normally connecting its respective two-way speaker between its respective signal line and said common control line to facilitate, without manipulation of its remote station switch means, audible reproduction of an audio frequency signal transmitted from said signal generator means to said remote station over said respective signal line and said common control line in response to activation from said central station of the call switch corresponding to said remote station, said 11 switch means each having a second condition in which its respective twoway speaker is connected between said audio lines, and said n switches each having a third condition in which its respective two-way speaker is connected between said audio lines and in which a control signal is placed on said control and at least one audio line to cause said amplifier control means to alter the direction of amplification of said amplifier.

2. The system of claim 1 wherein central station has a second two-way speaker remote from said first two-way speaker; and further including a central station speaker selector switch connected between said first and second central station speakers and said amplifier means for alternatively connecting said central station speakers to said amplifier means; a second set 11 call switches at said central station and associated with said second speaker, each of said n switches corresponding to a different one of said n remote stations for transmitting an audio frequency signal between said signal generator means and a selected remote station via the signal line connected to the selected remote station; and call switch responsive control means responsive to said first and second sets of call switches for controlling said selector switch to connect to said amplifier means only one of the central station speakers when a call switch is actuated, the one central station speaker connected being that WhlCh 15 associated with the call switch set having the actuated call switch.

3. The system of claim 2 wherein said remote station switch means each have a fourth condition wherein a door unlock signal is placed across said control line and one of said audio lines; said system further including first and second door control mechanisms for controlling doors associated with said first and second central station speakers, respectively, said door control mechanisms being jointly responsive to said call switch responsive control means and to said door unlock signals for actuating, in response to a door unlock signal, only the door unlock mechanism associated with the call switch set having the actuated call switch.

Claims

1. An intercommunication system comprising n remote stations each having a two-way speaker, a central station having a first two-way speaker, first and second audio lines each connected to each of said n remote stations and connectable to said central station two-way speaker, audio frequency signal generator means, n signal lines each connected between said signal generator means and a different one of said n remote stations, a first set of n call switches at said central station and associated with said first speaker, each of said switches corresponding to a different one of said n remote stations for transmitting an audio frequency signal between said signal generator means and a selected remote station via the signal line connected to the selected remote station, a single common control line connected to each of said n remote stations and said central station, audio frequency amplifier means connected in said audio lines, amplifier control means connected to said amplifier and between said single control line and at least one of said audio lines, said control means responsive to a control signal on said control and at least one audio line from said remote stations for amplifying, on an alternative basis, communications on said audio lines in one direction from said remote stations and in another direction from said central station, n switch means respectively at different ones of said remote stations, each of said switches normally connecting its respective two-way speaker between its respective signal line and said common control line to facilitate, without manipulation of its remote station switch means, audible reproduction of an audio frequency signal transmitted from said signal generator means to said remote station over said respective signal line and said common control line in response to activation from said central station of the call switch corresponding to said remote station, said n switch means each having a second condition in which its respective two-way speaker is connected between said audio lines, and said n switches each having a third condition in which its respective two-way speaker is connected between said audio lines and in which a control signal is placed on said control and at least one audio line to cause said amplifier control means to alter the direction of amplification of said amplifier.

2. The system of claim 1 wherein central station has a second two-way speaker remote from said first two-way speaker; and further including a central station speaker selector switch connected between said first and second central station speakers and said amplifier means for alternatively connecting said central station speakers to said amplifier means; a second set n call switches at said central station and associated with said second speaker, each of said n switches corresponding to a different one of said n remote stations for transmitting an audio frequency signal between said signal generator means and a selected remote station via the signal line connected to the selected remote station; and call switch responsive control means responsive to said first and second sets of call switches for controlling said selector switch to connect to said amplifier means only one of the central station speakers when a call switch is actuated, the one central station speaker connected being that which is associated with the call switch set having the actuated call switch.