US2162547A - Communication system - Google Patents

Description

June 13, 1939. R. H, CAMPBELL COMMUNICATION SYSTEM 2 Sheets-Sheet l Filed NOV. ll, 1937 June 13, 1939. R H. CAMPBELL 2,162,547y

COMMUNICATION SYSTEM Filed Nov. 11, 19:57 2 sheets-sheet 2 w 1 1 13 muhq UU.,

W H111 1F11 I il!! Q THW m N *I n Mm u] 3 Y 1 l N l gl Patented June 13, 1939 UNITED STATES ooMMUNIcA'rroN SYSTEM Richard H. Campbell, Racine, Wis., assignor to Webster Electric Company, Racine, Wis., a corporation of Wisconsin Application November 11, 1937, Serial No. 173,988

, 22 Claims.

The present invention relates to communication systems and particularly to telephonie communication systems in which suitable voice receiving and transmitting means. such as loud speaker units of the type comprising a voice coil and permanent magnet, are employed for the dual function of receiving and transmitting, the iiuctuations in electrical current created when a particular unit is utilized as a transmitter being i amplified by suitable amplifying means.

In systems of this type, which are nding an increased use in apartments, hotels. stores and the like, it is customary to provide one or more of the stations comprising the system with amplifying means and a communication control switch adapted selectively to be operated by an operator at the station. The switch is designed customarily to occupy a normal position, usually the listen" position, from which it is operable to a displaced "talk" position. It has been found desirable, as set forth in my application Serial No. 171,627, filed October 29, 1931, to utilize the same switch to control the operativeness of the amplifierby cutting oil' the "B supply of the latter when the switch is operated to a iur-ther displaced position.

Systems of the ty'pe described are very satisfactory where secrecy of communication is not desired nor necessary. However, in some installa- 'tions, such as apartment houses, lobbies of hotels, and factory entrances, to enumerate a iew, it is oftentimes desirable to prevent others than the operator from hearing messages transmitted from a distance.

It is the primary object of the invention to provide a new and improved linter-communicating system enabling an operator simplyand easily to change over from loud speaker to earphone reception whereby the operator alone is able to hear received messages.

A further object of the invention is to provide a system in which the change-over from loud speaker to earphone reception is made automatically upon removal of the earphone from its normal inoperative position.

-A further object of theinvention is to provide a system in which the operation of the system. in so far as manipulation of the communication control switch is concerned, remains unaffected by such av change-over.

A still further object of the invention is to provide a new and novel inter-communicating system comprising a loud speaker unit, an earphone and communication control switch that is operable from a normal "listen" position to a dis- (Cl. 179-1) l placed "talk position during operation of the system with the loud speaker unit alone and that is operable into another displaced position, in which it is adapted to remain until positively removed therefrom, to connect the earphone and 5 loud speaker unit in circuit as receiver and transmitter, respectively, so that two-way communi' cation may be carried on between two or more stations in which the communication control switches lhave been operated to said other displaced positions.

Other advantages and objects oi the present invention will become apparent from the ensuing description, in the course oi which reference is had to the accompanying drawings, in which:

Fig. 1 is a schematic representation of one embodiment of the present invention, and

Fig. 2 is a similar representation of a modied form thereof.

Referring now to Fig. 1, the reference numerals Il and l2 designate voice receiving and transmitting means of the loud speaker type comprising a permanent magnet and a voice coil suspended in the eld thereof. In so far as the present invention is concerned, other types of "loud speaking" receivers may be substituted for those speciiically disclosed herein. The speaker units are located at stations l and 2, respectively, which are located remote from each other and from other stations included in the system.

In the embodiment now being described, the apparatus at stations I and 2 is identical in all respects. The stations are provided with amplifiers I3 and Il, preferably comprising a plurality of stages of audio amplication and supplied with power from suitable sources through pairs of conductors I5 and I6. The ampliiiers comprise a number oi electronic vacuum tube devices having their cathodes heated at all times and adapted to be rendered operative immediately upon closure `of the B supply circuit, which yis accomplished upon predetermined operation of the combined power and communication control switches i1 and I8 at the two stations.

These switches, which will be referred to hereinafter simply as Vcontrol switches, are of the multi-pole, multi-position type and comprise five blades lil to 23, inclusive, and 24 to 2l, inclusive, respectively. mechanically inter-connected for simultaneous operation. They are operable from their normal positions, in which they are shown, into a first displaced position below the normal one and into a second displaced position above the normal one. They are vbiased for movement from their first displaced positions to their nor- 55 mal positions by springs 29 and 30, respectively. for a purpose that will appear hereinafter.

The stations are also provided with selector switches 33 and 3| for changing over from loud speaker to earphone reception. They are oi' the well known hook type adapted to support earphones 35 and 3B, respectively. Ihe switches occupy one position when theY receivers are suspended therefrom and are automatically operable into another position upon removal of the' earphones to change-over from loud speaker to earphone reception at the particular station at which this operation is eiected.

Stations I and 2 are adapted to be connected in communicative relation with each other through inter-station conductors 31 and 38, the latter constituting what is usually termed the common conductor. The stations are also provided with station selector switches 33 and 40 operable to connect the stations with which they are associated to the other stations oi' the system upon actuation thereof into engagement with any of the conductors II to l5 which may be considered as leading to all stations (stations 3 to 5 inclusive, not shown). The common conductor 33 may be extended to all stations through a conductor 46.

The selector switches 39 and 40 have been, for the purpose of simplicity, illustrated as making a direct connection between stations I and 2. but it should be understood that each station has its own inter-station conductor with which the selector switch is normally in engagement, so that any station can be called simply upon operation of the selector switch at the calling station into engagement with the inter-station conductor associated with the station being called.

Returning now to a more detailed description of the control switches, it may be noted that at station I the B supply is controlled by blade I 9 and the communication circuits by the remaining blades. 'Ihe B supply circuit is broken by blade I9 .in the normal position oi the switch, but is completed by interconnection of conductors 5I and 52 by the blade whenever the control switch is operated to either of its displaced positions.

The connection of the loudspeaker unit II to ampliier I3 and inter-station conductors and 38, which together may be termed the interstation communication circuit, is controlled by blades 28 to 23. inclusive. These blades are so arranged in the various circuits to be described that ln the normal position of the switch, with the earphone 35 in its usual position on hook switch 33, the loud speaker unit is connected to the inter-station communication circuit for reception. 'I'he blades are also arranged in such manner that the system can be operated with either loud speaker or earphone reception and, particularly, are so arranged that when the latter type of reception is selected and the communication control switch operated into a predetermined position, no further operation of the latter is required.

'I'he loud speaker unit is connected directly to blades 23 and 23 through conductors 53 and 54. These blades are adapted to make engagement with the amplier input leads 55 and 56, respectively, in either ot the two displaced positions of the control switch. The inter-station conductors 31 and 38 are connected to switch blade 2l and to a plurality of contacts associated with blades 22 and 23 that are inter-connected by conductor 51. The connections are such that conductor 38 is normally connected to conductor 54 and in the displaced positions of the switch It is connected to an amplier output lead 58 through blade 22. 'I'he other amplier output lead 53 is connected to conductor 60 leading to contacts selectively engaged by blade 2| in the displaced positions of the control switch.

In the normal position off the communication control switch and with the earphone on its hook, the loud speaker is connected to the interstation communication circuit through a previously described circuit established through blade 23 and a circuit including blade 20, conductor 5I, hook switch 33 in engagement with a contact associated with the last named conductor, conductor 62, and a potentiometer connection through the resistor 63 that is connected direct- 1y across conductors 31 and 38. It can be readily noted that the potentiometer arrangement provides a simple means for varying the volume of received messages.

To complete the detailed description of the circuits at station I, it may be stated that when the earphone is removed from its hook a circuit is completed placing the earphone across the inter-station conductors through a circuit including conductor 64, condenser 55, conductor 66 and through conductor 62 to the potentiometer resistor 53.

The B supply at station 2 is controlled by blade 2l which is adapted, when the communication control switch is operated to its displaced positions, to complete a connection between conductors 1I and 12. Loud speaker unit I2 is connected by conductors 13 and 14 directly to blades 25 and 28 which, in turn, are adapted` to engage contacts leading through conductors 15 and 16, respectively, to the input of the amplier.

The inter-station conductors 31 and 3B are connected to blade 26 and to a plurality of contacts associated with blades 21 and 23 that are all inter-connected by a conductor 11. The amplifier output leads 1B and 18 are connected to, blade 21 and a pair of contacts inter-connected by conductor III and associated with blade 26. The loud speaker unit is normally connected to the inter-station conductors through blade 28 and through a circuit including blade 25, conductor BI, hook switch 34, conductor 82, and the potentiometer resistor 83 which is connected across conductors 31 and 38. When the earphone 36 is lifted from its hook it -is connected to the communication circuit through conductor 84. condenser` 85, conductor 36, hook switch 34, and conductor 82 leading to the resistor 83.

In the description of the operation of the system it is assumed that the power supply leads I5 and IB are connectedto suitable sources to condition each ampliiler for immediate operation whenever its B supply circuit is completed. However, it should be noted that any station can be called even though its amplifier is not so conditioned, because theloud speaker unit is normally connected to the communication circuit for reception. Thus, if the operator at station I desires to call the operator at station 2, the former operates switch I1 to its lower displaced position. This operation completes the B supply circuit to render the amplifier operative and connects the loud speaker unit II to the input of the ampller and the inter-station conductors 31 and 33 to the output ot the ampliier.

The input circuit extends through conductors 53, 54, blades 28 and 23 in their lower displaced positions. Aand conductors 55, 58. The output circuit extends to the inter-station conductors through conductors 58. 80 and 60, and blades 2| and 22. Since the speaker unit I2 at station 2 is normally connected to the inter-station conductor through blades 2l and 28 oi' control switch I8l and hook switch Il, the signals originating at station I are transmittedto station 2 and received at the latter at a volume dependent upon the setting of the potentiometer comprising conductor-82 and resistor 89. After calling, the operator at station I releases switch I1 which is returned by spring 29 to its normal position, and if the operator at station 2 desires to answer, he actuates switch I to its lower displaced position. The release of switch I1 and depression of switch I8 reverses the 'direction ot communication.

In some installations, as in oillces where the system is utilized for dictation from a managers oiiice, for instance, at station I to a stenographer located at station 2, it would be inconvenient for the manager to hold the communication control switch in its lower displaced position during dictation. To avoid thisA inconvenience, the operator at station I can operate control switch I1 to' its upper displaced position, thereby conditioning station I for transmission until the switch is manually returned to one of its other positions.

In the upper displaced `position the speaker unit is connected to the input and the interstation conductors 31 and 98 to the output through circuits identical with those previously described, with the exception that the blades 20 and 23 are operated into engagement with the upper contacts.

In case itis desired for any reason whatever to render persons other than the operator at station 2 from overbearing the conversation, the operator at station 2 can `remove earphone 3G from hook switch 9|.. The latter disconnects conductor 82 from conductor 8| and connects it to conductor B6. thereby permanently connecting the earphone across the communication circuit. Lifting the earphone oil the hook at station 2 does not affect the circuit connections at station I in any manner and the operator at the latter station is able to talk to the operator at station 2 in either of the two modes described. Likewise; the operator at station 2 can manipulate his switch in the same manner to transmit to station I. That is, switch `I0 can be depressed from its normal listen position to its lower displaced or talk position.

A further advantage of the system is that twoway communication can be maintained without manipulation of the controlV switches by operation thereof to their upper displaced Vpositions after the earphones have been taken oil their hooks at both stations. Upon such operation the loud speaker units are connected to the inputs of their respective amplifiers, the inter-station conductors areconnected to the amplifier outputs, and the earphones across a portion of the resistors. Two-way communication may -b e maintained until either or both of switches I1 and I0 are manually actuated to some other position.

When the system comprises only stations I and 2, then only two inter-station conductors 31 and 98 are required. Whenever other stations are added, each station is provided with its own individual inter-station conductor. Thus, station I can communicate with stations l, I and 5 simply upon operation of selector switch 81 into engagement with these conductors. Thereafter the operator, in so far as commimication is concerned, is identical with `that described above.

In Fig. 2 there is disclosed a somewhat dlilerent type oi system comprising a single master station A and a plurality of dependent stations remote therefrom and from each other and indicated in the present instance by reference letters B and C. Station A is provided with aloud speaker unit 9| adapted to be utilized as a receiver and a transmitter and is adapted to be selectively connected in circuit with the inter-station conductors or the input and output of an amplifier 92 by means of a combined power and communication control switch indicated generally `by reference numeral 99. The amplifier 92 may be of the same general type as the previously described ampliers and supplied with power through conductors 94. 'Ihe amplifier is conditioned ior immediate operation upon the completion of the B supply circuit, which is accomplished by inter-connecting conductors 95 and 06 through one of the blades of the control switch 93.

The combined power control and communication switch is of the multi-pole, multi-position type and consists of three blades 91, 98 and 99, all mechanically inter-connected for simultaneous operation and operable into three positions. The switch is indicated in its oil position in which the B supply circuit is broken by switch biade 91 and is operable into an intermediate listen Position and to a lower talk position. It is biased for automatic return from the lower to the intermediate position by means of a spring IOI.

In the off position of the control switch voice coil |02 or loud speaker unit 9| is connected to an inter-station conductor |03 through blade 99, conductor |04, blade 98 and conductor |05. The other terminal of the voice coil |02 of the speaker unit 9| is grounded in order to reduce the number of conductors required in the system. In the intermediate position of the switch 93 the loud Speaker unit is connected to the output of the ampliiler and the inter-station conductor is connected to the input. The former is connected to the output through a circuit including the previously mentioned conductor |05, switch blade 98. conductor |00, a volume control resistance' |01, hook switch |08, conductors |09 and I|0. The circuit to the input is completed through a conductor |I| leading to ground. Inter-station conductor: |03 is connected to the input through blade 99, conductors I|2 and |I3. The other terminal. of the input is likewise grounded by conductor IH.

In the lower or talk position of the control switch 93, the loud speaker 9| is connected to the input of the ampliiler and the inter-station conductor is connected to the output of the amplifier. AThe former is connected to the input through conductor |05, switch blade 90 in engagement with conductor I I5, and the previously mentioned conductors ||3 and Ill. The interstation conductor is connected to the output of the amplier through switch blade 99, conductor IIS, and the previously mentioned conductors' ||0 and III.'

Provision is made at station I for substituting an earphone ||1 for confidential reception of messages from the remote stations whenever the earphone is lifted of! the hook switch |08. Upon such operation the earphone is connected directly to the output of the amplier through the previously mentioned conductors |09, ||0 and III through conductor H1, condenser H8 and conductor H9 leading to ground. The tone control resistor |2| can be connected in parallel to the earphone and condenser, if desired.

In a master system of the type now being described, two inter-station conductors lead from station to the remote stations. One of these is the previously mentioned inter-station conductor |03 and the other is conductor |22 which may be grounded at station I in convenient manner and similarly grounded at the remote stations B and C. The inter-station conductor |02 leads directly to station B and has a branch conductor |23 leading to station C. Conductor |03 is connected to one terminal of voice coil |24, the other terminal of which is grounded through conductor |25. The voice coil |26 of the receiver unit at station C is connected in parallel with that at station B by the branch conductor |23 and a conductor |21 leading to ground.

In the operation of the system last described, the system is normally inoperative with the switch in the oir position in which it has been illustrated. However, whenever it is desired to place the system in operation, the combined power and communication control switch 93 is actuated into its intermediate or listen position in which the loud speaker units at stations B and C are connected directly to the input of the arnpliiier through a circuit that has been previously described in detail. At the same time the loud speaker unit at station A is connected to the output oi the amplier so that operators at any of the remote stations may call the operator at station A. If the operator at the latter station desires to respond, he has merely to operate control switch 93 to its talk position, at which time the connections of the loud speaker units at the master and remote stations to the amplifier are reversed, the loud speaker units at the remote stations being connected to the output and the amplifier, and that at the master station being connected to the input of the amplifier.

It should be noted that the volume control resistance |01 is in circuit only when the loud speaker unit 9| at the master station is connected to the output of the amplier. The reason for this is that the ampliiier volume is adJusted to impress the normal signal strength upon the parallel connected loud speaker units at the remote stations and if the entire output of the ampliner were impressed across the single loud speaker unit at the master station distortion would result. By interposing the resistance |01 in circuit with the loud speaker unit at the master station, the distortion is-avoided.

Whenever the operator at the mastcrstation desires to prevent others in that vicinity from overbearing received messages, it is necessary for him simply to remove earphone ||`l from its associated hook switch IBB. This operation places the receiver directly across the output of the amplier through a previously described circuit. Then with the communication control switch in its intermediate position, the loud `Speakers at the remote stations are connected to the input and the earphone to the output of the amplier. The loud speaker unit 8| is not utilized as a receiver, because it is disconnected from the ampliiier circuit by the hook switch |08. When the operator at station A replies, he simply operates the control switch to its lowermost position, thereby connecting the loud speaker at station A to the input and the remote stations to the output of the ampliiler, just as in the previously described mode of operation. Thus, it may be seen that the loud speaker unit at the master station may be selectively utilized both as a transmitter and as a receiver, or simply as a transmitter without affecting the mode of operation of the control switch.

Although the invention has been disclosed in connection with the specic details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative oi the invention except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. In an intercommunicating system, the com bination including. a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone, a communication circuit, and switch means for controlling the establishment of circuits from the communication circuit to said unit and earphone, said switch means being so constructed and arranged that the unit can be selectively connected to said circuit for reception or transmission, or the unit and earphone can be connected to said circuit for transmission and reception, respectively.

2. In an intercommunication system, the combination including, a plurality of stations each having a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone, means including a plural position communication control switch and a selector switch for controlling the establishment of communication be tween stations, said switches being so arranged with respect to each other, the loud speaker unit and earphone that in one position of the selector switch the earphone is cut out of circuit and the control switch is selectively operable between two positions to connect the loudspeaker unit in circuit as a receiver and transmitter, and in another position of the selector switch the earphone is placed in circuit and the control switch is operable between the same positions to connect the loudspeaker unit in circuit as a transmitter only.

3. In an intercommunication system, the combination including, a plurality of stations, each having a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone, and means including a. manually operable communication direction control switch and a selector switch supporting said earphone and automatically operable from a normal position to a displaced position upon removal of the earphone for controlling the establishment of communication, said switches being so arranged that with the selector switch in its normal position the communication control switch is selectively operable to connect the loudspeaker unit in circuit as a receiver or transmitter, and with the selector switch in its displaced position, the communication control switch is operable only to connect the loud speaker unit in circuit as a transmitter.

4. In an intercommunication system, the combination including, a plurality of stations each having a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone, and switch means for controlling the communication circuits, said switch means being so constructed and arranged that each station can be conditioned for reception or transmission through said loud speaker unit or for concurrent reception and transmission through said earphone and loud speaker unit.

5, In an intercommunication system, the combinauon including, a mummy or stations each having a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone, and switch means for controlling communication between stations, said switch means being so constructed and arranged that oneway loudspeaking communication in either direction can be carried on through predetermined alternate operation into predetermined positions oi said switch means at two stations, and two-way communication between the' two stations can be carried on without further operation ot said switches upon operation thereof into another position wherein the loudspeaker is connected in circuit as a transmitter and the earphone as a receiver. t

6. In an intercommunication system, the combination including, a plurality of station's each having a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone. and means including a plural position communication control switch and a selector switch for controlling communication between stations, said switches being so arranged with respect to each other, the loud speaker unit and earphone, that in one position of the selector switch, the earphone is cut out of circuitand the control switch is adapted to be operated between two positions for connectingthe loudspeakswitch is adapted to be operated into a. third position 'in which the loud speaker unit is utilized solely as' a transmitter and the earphone as a receiver.

7. In an intercommunication system, the combination including a plurality of stations, each having a loud speaker unit adapted to be used both as a receiver and a transmitter, an earphone, means including a plural position communication control switch and a selector switch for controlling communication between stations, said switches being so arranged with respect to each other, the loud speaker unit and earphone, that in one position of the selector switch the earphone is cut out of circuit and the control switch is ,adapted to be operated between two positions for controlling the connections of the loud speaker unit and the direction of communication, and in another position of the selector switch the earphone is placed in circuit and the control switch is adapted to be operated into a third position in which the loud speaker unit is utilized solely as a transmitter and the earphone as a receiver, and means for automatically'returning the control switch from a predetermined one of its two mst-mentioned positions to the other.

8. In an intercommunication system, the combination including, a plurality of stations each having a loud speaker unit adapted to be used both as a receiver and a transmitter, and earphone, and means including a manually operable communication direction control switch and a selector switch supporting said earphone and auboth as a receiver and a transmitter, an amplier with input and output connections, and a communication control switch, inter-station conductors between said stations, said communication control switches being operable to a first position for connecting said loud speaker unit to said interstation conductors and to second and third positions for connecting said loud speaker unit to the input of the amplifier and the output oi the latter to the inter-station conductors, and means for automatically returning said control switch from 20 apredetermin'ed one of said second and third positions to said rst position.

10. In a communication system the combination including. voice receiving and transmitting means, a communication circuit, amplifier means,

and switch means controlling the connections of the voice receiving and transmitting means and communication circuit to the input and output of said amplier, said switch means normally connecting the voice receiving and transmitting means directly to said communication circuit and being operable to a plurality of displaced positions for connecting said voice receiving and transmitting means to the input and the communication circuit to the output of the amplifier.

11. In'a communication system the combination including, voice receiving and transmitting means, a communication circuit, amplier means, switch means controlling the connections of the voice receiving and transmitting means and com- 40 munication circuit to the input and output oi said amplifier, said switch means normally connecting the voice receiving and transmitting means directly to said communication circuit and being operable to a plurality of displaced positions for connecting said voice receiving and transmitting means to the input and the communication circuit to the output of the amplifier, and means for automatically returning said switch means from one of said displaced positions to its normal position. 12. In an intercommunication system, the combination including, a plurality 'of stations each having a loud speaker unit adapted to be used V5 both as a receiver and a transmitter, an earphone,

an amplifier with input and output connections, a communication control switch, and a. switch means controlling the circuitl connections of the earphone, and inter-station conductors between stations, each communication control switch being operable to aV iirst position for connecting its associated loud speaker ,unit to said inter-station conductors, and to second and third positions for connecting said loud speaker unit to the input of the amplifier and the output of the latter to the inter-station conductors, and said secondmentioned switch being operable to connect the earphone directly to said inter-station conductors and so modify the circuit connections that the communication control switch is eiiective only when operated to its second or third position.

13. In an intercommunication system, the combination including, a. loud speaker unit. an earphone, an amplifier having input and output connections, an inter-station communication circuit, a communication control switch operable between predetermined positions and circuits controlled thereby for selectively connecting said loud speaker unit to said circuit for reception and to .said amplier input and the output of the latter to said circuit for transmission, and switch means for changing the control circuits in such manner that the operation of the control switch between said predetermined positions substitutes the earphone for the loud speaker unit during reception.

14. In an inter-communication system, the combination including, a loud speaker unit, an earphone, an amplifier having input and output connections, an inter-station communication circuit, a communication control switch operable between predetermined positions, and circuits controlled thereby for selectively connecting said loud speaker unit to said circuit for reception and to said amplifier input and the output of the latter to the said circuit for transmission, and switch means supporting said earphone and automatically operable to change the control circuit connections upon removal of the earphone therefrom in such manner that the operation of a control switch between said predetermined positions substitutes the earphone for the loud speaker unit during reception,

15. A unit for use at a station in an intercommunicating system, including in combination. a microphone, an amplifier, switch means operable into a plurality of positions for connecting said microphone to the input of said ampliiier, and biasing means adapted to act upon said switch means when it is operated into one of its positions tending to move said means from said one position.

16. A unit for use at a station in an intercommunicating system, including in combination, an amplifier comprising a vacuum tube conditioned for operation upon the connection of the anode of the vacuum tube to a source of B" potential, a microphone, and switch means operable into a plurality of positions for connecting said microphone to the input of the amplifier and simultaneously connecting said anode to the source of B potential.

17. A unit for use at a station in an intercommunicating system, including in combination, an amplifier comprising a vacuum tube conditioned for operation upon the connection of the anode of the vacuum tube to a source of "B potential, a microphone, plural position switch means occupying a normal position in which the microphone is disconnected from the amplifier and the anode from the source of "B potential, circuits connecting the microphone to the input of the amplifier and the B" potential to the anode adapted to be closed by said switch means upon operation thereof into a displaced position, circuits connecting the microphone to the 'input of the amplifier and the B potential to the anode adapted to be closed by said switch means upon operation thereof into a second displaced position, and biasing means tending to return the switch means from one oi' its said displaced positions to its normal position.

18. In an intercommunicatlng system of the loudspeaking type comprising a plurality of stations each provided with a loudspeaker unit adapted to be used both as a microphone and a receiver, an amplifier conditioned for instantaneous operation upon the supply of B' potential thereto and interstation communication circuits, the combination including, a communication control switch at each station occupying a normal position and operable into a plurality of displaced positions, communication and "B supply circuits controlled thereby. said switches being so arranged with respect to the loudspeakers, interstation communication circuits and B" supply circuits that when the switches occupy their normal positions the B potential is disconnected from the amplifier and the loudspeakers are connected to an interstation circuit and when the switch at any station is operated to either of its displaced positions the loudspeaker is connected to the amplifier input, the interstation circuit is connected to the output, and the B supply circuit connected to the amplifier to render the latter operative.

19. In an intercommunicating system of the loudspeaking type comprising a plurality of stations each provided with a loudspeaker unit adapted to be used both as a microphone and a receiver, an amplifier conditioned for instantaneous operation with the supply of B" potential thereto and interstation communication circuits, the combination including, a communication control switch at each station occupying a normal position and operable into a displaced position, interstation communication and B" supply circuits controlled thereby, said switches being so arranged with respect to the loudspeakers, interstation communication circuits and "B supply circuits that when they occupy their normal positions the B" potential is disconnected from the amplifier and the loudspeakers are connected to an interstation circuit, and when a switch at any station is operated to its \displaced position the loudspeaker thereat is connected to the amplifier input, an interstation conductor to the amplifier output and the B" supply to the amplifier to render the latter operative, and biasing means tending to return the switch from its displaced position to its normal position.

20. In an intercommunicating system, the combination including, a loudspeaker unit of. the type adapted to be used as a microphone and a. receiver, an earphone adapted to be used as a receiver, an amplifier having input and output connections, an interstation communication circuit, a communication control switch operable between predetermined positions and circuits controlled thereby for selectively connecting said loudspeaker unit to the input of the amplifier and the output of the latter to the communication circuit, or vice versa, and switch means supporting said earphone and automatically operable to connect the earphone directly to the output of the amplifier upon removal of the earphone therefrom and operable to change the connections between the loudspeaker unit, amplifier, and communication control switch in such manner that the vlatter is operable between said predetermined positions for selectively connecting the loudspeaker unit to the input of the amplifier and the communication circuit to the output, or the communication circuit to th'e input,

of the amplifier.

21. In an intercommunicating system, the combination including, a loudspeaker unit of the type adapted to be used as a microphone and a receiver, an earphone adapted to be used as a receiver, an amplifier having input and output connections, an interstation communication circuit, a communication control switch operable `between predetermined positions and circuits controlled thereby for selectively connecting said 22. A unit for use at a station in an intercommunicating system of the loudspeaker type, including in combination, a microphone, an amplier having input terminals, a manually operable switch connected to said microphone and operable into two displaced positions, and circuits adapted to be closed by said switch in its said displaced positions, whereby the microphone is connected to the input of the ampliiler when the switch is operated into either of its displaced 10 positions.

RICHARD H. CAMPBELL.

CERTIFICATE 0F CORRECTION.

Patent No. 2,162,51i7.

June 15, 1939.

RICHARD H. CAMPBELL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, second column, line 5B, claim 20, after the word "operable" insert also; and

that the said Letters Patent should be read with this correction therein that the same niay conform to the record of the case in the Patent office.

signed and sealed this 12th my of september, A. D. 1959. C

(Seal) Henry van Arsdale,

Acting Commissioner of Patents.

22. A unit for use at a station in an intercommunicating system of the loudspeaker type, including in combination, a microphone, an amplier having input terminals, a manually operable switch connected to said microphone and operable into two displaced positions, and circuits adapted to be closed by said switch in its said displaced positions, whereby the microphone is connected to the input of the ampliiler when the switch is operated into either of its displaced 10 positions.

RICHARD H. CAMPBELL.

CERTIFICATE 0F CORRECTION.

Patent No. 2,162,51i7.

June 15, 1939.

RICHARD H. CAMPBELL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, second column, line 5B, claim 20, after the word "operable" insert also; and

that the said Letters Patent should be read with this correction therein that the same niay conform to the record of the case in the Patent office.

signed and sealed this 12th my of september, A. D. 1959. C

(Seal) Henry van Arsdale,

Acting Commissioner of Patents.

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