US2484748A - Selective electric signaling system - Google Patents

Description

Oct. 11, 1949. E. s. RUTH 2,484,748

SELECTIVE ELECTRiC SIGNALING SYSTEM Filed Feb. 4, 1948 4 Sheets-Sheet 1 7:22 111 1 A 221 Z 5 A ZIQQ 4 4a 1e INVENTOR HTTORNEYS SELECTIVE ELECTRIC SIGNALING SYSTEM Filed Feb. 4, 194a 4 Sheets-Sheet 2 g BUZZER ITTORNEY9 221! m; 22a Ill 2'13 224 I 220 218 J INVENTOR B Eda/mu J. ijullz v V Y I I J i m flvuzw aLM (Oct. 11, 1949. E. s. RUTH v 2,484,743

SELECTIVE ELECTRIC SIGNALING SYSTEM I Filed Feb. 4, 1948 4 Sheets-Sheet 4 16a INVENTOR f2: {Eda W46! iii/ BY W 7 v.

ATTORNEYS Patented Oct. 11, 1949 2,484,748 SELECTIVE ELECTRIC SIGNALING SYSTEM- Edward S. Ruth, Norwalk, Conn., assignor to Edwards and Company, Inc., Norwalk, Conn., a corporation of New York Application February 4, 1948, Serial No. 6,297

Claims. (Cl. 177353) This invention relates to selective electric sigfor indicating at the master station that an individual station has been called and for further indicating at the master station the receipt of a signal by an individual at the called station;

Figure 2 is a circuit diagram of a modified 55 master station circuit embodying the useof --a naling system. telephone type of calling dial for signaling-indi- An object of the invention is to improve sel'ecvidual stations; tive signaling systems such as signaling circuits Figure 3 is a circuit diagram showing a further for use in apartment houses, dormitories, schools 5 modified master station circuit having a common and the like and for other applications where sereturn signal device; and lective signaling is required. Figure 4 illustrates a further modified master Another object is to provide a selective signalstation circuit. ing system requiring a reduced number of signal- In apartment houses, dormitories,--school's and ing conductors. lo a number of otherlocations there-is frequently A further object is to provide a signaling sysa need for signaling systems whereby anyone of tem for signaling any one of several stations a number of rooms or stations can be calledfrorn selectively over conductors which are common to a central location or master station. Thus, in two or more of the stations. dormitories an office or attendants desk is free- A still further object is to provide a selective l5 quently located near the entrance to the building signaling system for calling any one of a pluor, in the case of agroup of buildings, in one of rality of stations from a master station and for the buildings of the group. When a visitor calls signaling the master station from the individual at the attendants desk for one of the occupants stati ns. of the dormitory or when a telephone call is re- A specific object of the invention is to provide ceived on the house telephone it is usually necesa return call system for selective calling stations sary to provide some form of electric calling syslocated in various rooms in a building or group tem whereby the attendant can signal the room of buildings from a central switchboard or master of one of the occupants and receivea signal back station. from the occupant indicating that the calling A further object is to provide a signaling syssignal has been received Buzzer systems have tem for calling a plurality of individual station-s een p vided n he past qu r ng a Pair O selectively from a master station and for notifyconductors leading to each call station or at least ing the master station of the receipt of the signal one conductor individual to each station. 7 by the individual stations. In apartment houses where no attendant is ther objects are to provide suitable circuits provided a pu bu P el fr q and apparatus for carrying out the aforemencated at the entrance to the building to enable tioned objects. a caller to call any individual apartment and Other objects of the invention Will be apparent push buttons are provided in the apartment "for from the following description and accompanyanswering the-call or for unlatching the entrance ing drawings taken in connection with the apdoor to the building. These likewise require at pended claims. least one conductor to each apartment station.

The invention accordingly consists in the fea- The present invention contemplates a circuit tures of construction, combination of elements, in which several stations areserved by common and arrangement of parts as will be exemplified ndu or he arran ment in such that inin the structures to be hereinafter described and dividual Conductors are not q d 1 83 the scope of the application of which will be indi- Station and means are provided whe eby any cated in the following claims. station may be called or may signal the master In the accompanying drawings in which are i n Wi hout efiecti-ng he signaling devices shown by way of illustration several possibl emassociated with other stations. bodiments of my invention: The invention makes possible a great reduc- Figure 1 is a circuit diagram of a return n tion in the size of the" master station switchboard selective signaling system embodying features of qu d W h s t t ater Ope c the invention and comprising a master station ciency, reduced space requirement and greater or switchboard and a plurality of individual staportability and convenience of use of the master tions to be called, together with signaling means station.

According to the preferred method'of practicing the invention rectifier means are associated with the individual stations so that certain of the signaling apparatus at panel.

represent the drawing,

1 according to ing devices associated with uncalled stations or any inactive parts of the master station during the calling of an individual station or the calling of the master station from an individual station.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method or procedure and the construction of parts without departing from the spirit of the invention. In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the drawings, Figure 1 shows a selective electric signa1ing system suitable for calling the individual rooms of a dormitory or apartments of an apartment house or an aparta ment house roup from a central point such as an operator-attendant switchboard or a signaling The portions of the circuit on the left hand'part of the drawing to the left of the dot and. dash line represent those parts which are located at the master station or switchboard and the circuits on the right hand part of the drawing individual room or apartment station circuits. The conductors shown crossing the dot and dash line are the ones extending from the master station to the various groups of individual stations. It will be noted that these are Irelatively few in number and since they may be of considerable length where the separation of the master station from the call stations is great, the present circuit arrangement represents a considerable saving in wiring arrangements over prior art arrangements requiring one or more conductors connecting each individual station with the master station.

Assuming that the circuit is installed in a dormitory the groups of stations shown on the right hand part of the drawing may represent the stations located in the individual dormitory rooms. For purposes of illustration it will be assumed that the lowermost four stations shown in the indicated by reference numerals Nil, 20|, -30| and MN, are the stations located in the first room on the first, second, third and. fourth dormitory floors respectively. The next four stations indicated by numerals I02, 202, 302 and 402 will then represent the stations located respectively in the second room on each floor and so on to the uppermost stations shown, which will represent the signaling station located in room 404; in other words, the fourth room on the fourth floor of the building. While not necessarily so, all of the room stations will generally be similarly equipped. Station 404, as illustrated,

buzzer |0, an answering key N and, the present invention, a half-wave rectifier |2 such as a plate rectifier of the copper oxide or selenium type. The back contact l3, answering key N, buzzer l and rectifier I2 are all connected in series between terminals I4 and I5, which represent the terminal connections to the two signal conductors entering the room. An answering conductor I6 is also provided connecting the front contact ll of answering key M at the station.

At some or all of the stations it may be desirable also to provide visual indicators such as a drop annunciator in addition to the buzzer. This station 304 is provided, as shown, with a drop annunciator l8 whose winding is connected in series with buzzer l0.

comprises a When the room is called the buzzer will operate to give an audible signal,

. individual room stations I push buttons at the same time drop |8 will fan to give visual indication that the room has been called. When the occupant answers drop |8 can be manually reset.

The master station comprises a switchboard provided with a series of telephone jacks comprising sleeve contacts such as 2|, 22, 23 and 24 and tip contacts 3|, 32, 33 and 34. The switchboard is also provided with a series of push but tons such as push buttons 2, 3 and 4.

Switchboard lamps 4|, 42, 43 and 44 are associated respectively with the telephone jacks. An individual lamp control relay is associated with each jack and is provided with relay contacts 8|, 82, 83 and 84 respectively for closing the lamp energizing circuits 9|, 92, 93 and 94 respectively in response to the energization of operating windings 5|, 52, 53 and 54 respectively of the relays. A lamp energizing transformer 25 has its secondary winding connected at one end to common conductor 25 leading to all of the lamps and at the other end to common conductor 21 leading to one of the contacts of each of contact pairs 8| to 84, the other contact of each pair being connected respectively to the individual lamp energizing circuits 9| to 94 respectively. Relay reset windings 6|, respectively are associated with respective lamp control relays for opening the lamp circuits after they have been closed by the operating reset windings. Each of the reset windings has connected in series with it a half-way rectifier, namely rectifier H to 14 respectively. Each of the reset windings are connected between common conductor 26 and signaling conductors M2, I I3 and I I4 respectively leading respectively to the individua1 room station groups having the same last digit. For example, signaling conductor ||4 leads to terminal l4 and hence to keys H and I04 to 404 inclusive.

A second power supply transformer 28 for supplying signaling current has its secondary winding connected between one terminal of each of 2, 3 and 4 and. the sleeve contact 29 of the switchboard plug. The tip contact 30 of the plug is connected by conductor 35 through normally-open push button switch 36 to common conductor 21. Push button 36 is located at the master station for the purpose of resetting the signal lamp relays in case a called station does not answer.

Push buttons to to signaling conductors la, 2a, tively which lead to all of the respective floor.

The operation as follows:

When the operator at the master station wishes to call an individual room station, say room 404, she inserts the switchboard plug in to the jack associated with all of the rooms ending in the digit 4, namely jack 24 in the present example.

4 respectively are connected 3a and 4a respecroom stations on a of the system can be carried out She then pushes thev push buttons associated with the floor desired. In the present instance. Push button 4.

62, 63 and 64 sleeve 24 of the switchplug and conductor 37 to the opposite terminal of the secondary winding of transformer 28. Signaling current through this circuit operates buzzer II] to give an audible signal at individual room station 494 and energizes relay winding 54 to close relay contacts 84 to light signal lamp 44. The lamp energizing circuit extends from the sec ondary winding of transformer to conductor 26, lamp 44, conductor 94, rela contacts 34, and common conductor 27 back to transformer 25. This gives a visual signal or indication at the switchboard that the room has been called.

When the occupant of the room hears the buzzer he is supposed to answer by pressing key I I momentarily. As key II is pressed a reset circuit is closed to extinguish signal lamp 44 as follows:

From the right hand end of transformer 25 through common conductor I5, front contact I! of key II, key I I, the individual room circuit to terminal I4, conductor H4, rectifier l4, relay reset winding 64, common conductor 26 back to the left hand end of the secondary winding of transformer 25. This energizes winding 54 to open relay contacts 84 and thereby extinguish the lamp.

Should the room occupant fail to answer the operator at the master station can extinguish the lamp simply by pressing push button 36 which closes an operating circuit for reset winding 64 from transformer 25 through conductor 35, plug tip 3!], jack contact 34, rectifier l4, winding 64 and common conductor 26 back to the transformer.

The advantages and function of the rectifiers variously located in the circuit will now be apparent. First as to rectifiers individual room station; if room station 494 is being called current is supplied from the secondary winding of transformer 28 through push button 4 and conductor 4a to the room station. However, conductor 4a is also connected to all other stations on the fourth floor, such as stations 453i, 402, and 403 and hence one side of each of these room station circuits is bridged together. Similarly for stations on each of the other floors. However, certain groups of stations are also bridged together in another way as by conductors I I I, II2, I I3 and II 4 respectively, each of which is connected to a group of stations ending in the same digit. Without the rectifiers I2 in the circuit it would thus be possible for signaling current pasing through push button 4 and conductor to find its way back to the transformer, not only through station 404 which is intended to be called but also through several other paths such as follows:

From conductor 4a through station 403 and via the portion of conductor II3 which connects the stations ending in digit 3 together, then through stations I03, 203 and 303 to conductors Ia, 2a and 3a respectively. From these conductors the current can find a, ready return path to transformer 28 through stations I54, 204 and 304 respectively, conductor II4, relay winding 54, sleeve contact 24, plug sleeve 29, the plug being at this time inserted in sleeve 24, and conductor 3? back to transformer 28. However, with rectifiers I2 in each station circuit, each rectifier being directed to pass current through its station in the same direction, such a return path is blocked. Thus, while current could find its way via conductor 4a through station 403 to conductor H3 it would be blocked from finding a return path to the transformer since, at this time, the switchboard plug is not connected to sleeve 23 and the rectifiers I2 at individual stations I05, 253 and-303 are biased I2 located at each shown in Figure-2, the

6 in the direction which prevent current flow from conductor I I3 through the stations to conductors Ia, 2a and 3:1.

It will thus be evident, that by use of rectifiers I2 at the individual stations, a large number of room stations can be called from the central switchboard or master station, over a small number of conductors. In the example illustrated only'four floors and four stations per floor are indicated. However, it will be apparent that both the number of floors and the number of stations per floor can be increased or reduced. In general, one additional conductor leading from the master station is required for each additional floor being served by the switchboard and one additional conductor is required to be added for each additional group of room stations ending in the same digit. The advantages thus become more evident when a large building or a large number of stations are served.

The function of rectifiers II, 12, 13 and 74, located at the master station, is to prevent another condition in which room stations might be fortuitousl called. For'example, in the absence of rectifier 14 when station 4041s called the signaling current would also find a path for calling station 403 from push button 4 through conductor 4a, station 403, conductor H3, rectifier l3, winding 63, winding 64, conductor H4, winding 54, sleeve 24, plug sleeve contact 29, and conductor 37: back through transformer 23 to the push button. The rectifiers II to I4 prevent such sneak circuits which would interfere with the proper functioning of the system.

Figure 2 is a circuit diagram of a modified signaling system in which the stations are called by use of a telephone type dial in combination with a series of push buttons. The figure shows only the master station since the individual room station circuits are similar to those illustrated in Figure 1. Circuit conductors and circuit elements have been given the same reference numerals where they are similar in function and relative location in the circuit.

In addition to current supply transformers 25 and 23 a third transformer 2I2 is provided which current from full-wave rectifier 2I3 to dial 2M and winding 2 I8 of stepping switch 7 2I9 connects one contact of the dial to the rectifier and conductor 220 connects the other output terminal of the rectifier to winding 2IB of the stepping switch. I The dial pilot lamp 2I5 is connected between conof the stepping switch. Conductor 228 connects dial 2M to stepping winding 2 I 8.

If desired, for convenience, dial 2I4, pilot light 2I5, reset key '2I6, floor push buttons I, 2, 3 and 4, switchboard lamps 4|, 42, 43 and 44, resetting push button 35 and a buzzer 2II may all be installed at the operators location as indicated by the dashed rectangular 229, while stepping switch 2i! the relays having windings 5i to 54, current supply transformers 25, 28 and 2I2, and rectifier MS may be located in another space such as in a closet or in the basement of the building.

In operation of the dial system shown in Figure 2, assuming the operator wishes to call station 424 (Figure 1) from the master station operator will simply dial another position.

the. station digit on dial 2I-4, namely the numeral 4. Operation of the dial effects closure of the dial contacts momentarily four times in sequence. Each time the dial contacts are closed an energization circuit for stepping relay winding 2 I 8 is closed as follows:

From rectifier 2I3 via conductor 2.I9, dial 2I4, conductor 228, winding 218 and conductor 220 back to the rectifier. Energization of the winding 2I8 causes it to step contact arms 22l, 222, 223 and 224 ahead one position for each energization of the winding, the arms engaging cooperating contacts arranged in an are around them as they are advanced each step. Thus, arm 22E will be advanced to the fifth contact to close a circuit from transformer 28 via conductor 31, contact arm 22I, conductor 234, relay winding '54, conductor H4 to all room stations ending in the digit 4. When push button 4 is pressed, after this circuit has been established, the circuit is completed through room station .404, conductor 4a, push button 4, master station buzzer 2| I and conductor 2 I ll back to transformer 28, thereby operating the buzzer at room station 434 and simultaneously operating the buzzer at the master station to indicate to the operator that the station is being called. Relay winding 54 is also energized and operates its armature to close contacts 84, thus completing the circuit for signal lamp 44 giving a visual indication to the operator that a station ending in the digit 4 is being called.

When the person at station 434 answers by operating answering key II a circuit is completed for extinguishing lamp 44 as follows:

From the secondary winding of transformer 25 via conductor I3 through room station 404, then via conductor II4, rectifier 14, winding 64 and conductor 25 back to transformer 25.

Winding 64 thereupon opens contact 84 to extinguish the lamp.

Should no answer be received from the called station the operator can extinguish lamp 44 by momentarily pressing push button 36 which closes a circuit from transformer 25 via conductor i3, push button 36, conductor 235, selector switch arm 222, conductor 23B, rectifier 14, Winding 64 and conductor 26 back to the transformer. Contact arm 222, in the second bank of the selector switch, serves the purpose of connecting push button 36 to the reset winding of any digit dialed by the operator so that the indicating lamps may be selectivel extinguished before calling a second station. But, it also is possible for the operator to call a second station while she is awaiting a response from the first station by later redialling the first station for the purpose of extinguishing the first station signal by. push button 35 if a response is not received from that station.

In order to restore selector switch 2I'I to its normal or home position reset key 2I6 is provided. Thus, when the selector switch arms are on any selected station position the switch may be returned to normal by momentarily pressing push button 2E6. This closes a stepping circuit through interrupter contacts 225 of the stepping switch and switch arm 223 through operating winding 2I8. Contacts 225 are opened by the switch mechanism switch arms, thus allowing the stepping lever controlled by winding 2; to fall back. However, in doing so the lever closes contacts 225 to reenergize winding 2I8 and to advance the switch Hence, while resetkey2l6 is at each station position of the from transformer 28, during the calling of an inclosed the switch will automatically step around until it is returned to home position in which all contact arm circuits are opened and the winding H8 is de-energized.

Contact arms 22l, 222 and 224 are non-brid ing with respect to their associated contacts. That is, the circuit through the contact arms is momentarily opened while the arms are being transferred from one contact to the next succeeding contact of the ban Contact arm 223, however, is preferably of the bridging type so that the circuit is entirely under control of interrupter contacts 225 as long as reset key 2H5 is closed and the switch is not at home position.

Contact arm 224 closes the circuit at each digit position for pilot lamp 2l5 so that when a digit is dialed a pilot lamp flashes momentarily as the switch advances each position. This indicates to the operator that the selector switch is operating properly in response to the dial.

It is obvious that where the number of room stations on a floor exceed the number of digits on the calling dial the selector switch can be in two or more stages. The operator will then dial one number to select the tens digit thereby setting up a first rotary switch to a contact leading to a second rotary switch. The operator then dials the units digit to set up the selected position on the second switch. The two switches together then will complete the circuit to the room station selected when the desired floor key is pressed.

Figure 3 illustrates a further, and more simplified master station circuit for calling individual room stations similar to those shown in Figure 1. Such a circuit is useful, for example, at an unattended location such as the entrance to an apartment building where an operator is not provided. The master station comprises a switchboard having a series of jacks such as jacks 32I, 322, 323 and 324 connected to conductor III, H2, H3 and H4 respectively leading to the room stations. Push buttons corresponding to each floor are also provided such as push buttons I, 2, 3 and 4 for closing circuits over conductors Ia, to 4a respectively. The switchboard plug comprises a single sleeve contact 329 for engaging the sleeves of jacks 32I and the like.

An answering buzzer 3I I is also provided which is connected through rectifiers 33!, 332, 333 and 334 respectively to conductors III, H2, H3 and H4 respectively. Transformers 25 and 28 provide power supply for signaling current.

When a person wishes to call a room station he places the switchboard plug in the jack whose identification number ends in the digit of the call station desired and pushes the button corresponding to the floor on which the station is located. Thus, if station 404 is desired the plug is placed in jack 324 and push button 4 is pressed. This closes a signaling circuit from transformer 28 via conductor 31, plug contact 329, jack 324, conductor H4, room station 434, conductor 40., push button 4 and conductor 3H1 to transformer 28. In this system the room station is called but no indication is given by the switchboard during calling. However, when the person at the room station answers, a circuit is completed for operating answering buzzer 3lI from transformer 25 via conductor I6, room station 464, conductor H4, rectifier 334, buzzer 3H and conductor 26 back to transformer 25.

Rectifier 33I et al. prevent signaling current gal-84,3248

dividual station, from passing over conductors leading. to other groups of stations which might otherwise be fortuitously called. In thev absence of these rectifiers when station 404-is being called a circuit would also be closed for calling station 403- from jack 324 over conductor 3|? to jack 323 and over conductor H3 to the room station. Similar circuits would also be closed for calling allother stations on the fourth floor. However, rectifiers 3-3l to 334 are so biased that current sent over one conductor cannot find its way to any of the others.

Figure 41s a circuit diagram of a further modified system. This system is generally similar to the system illustrated in Figure l and the operation is substantially the same. However, in this system the rectifiers l2 are not located at the individual room stations but are grouped together in. a power unit which may be located at any convenient. location in individual. room stations are located, such as in the basement or a service room. The power unit indicated by a reference numeral 4l0 may include, in addition to the banks of rectifiers l2,

the transformer unit comprising transformers 25 and 28'.

The master station, indicated by reference numeral 4| I may be located at a point remote from the powerunit and from the room stations, such as; in. another building. The number of conductors connecting the master station with the power unit are relatively small, by virtue of the use of the rectifiers arranged according to the present invention.

A single room station 404 is illustrated in Figure 4, the other room. stations being similar and the connecting circuits being readily apparent from the diagram. Referring to room station 404 it will be noted that it is similar to the room station previously described in connection with Figure 1 with the exception that rectifier I2 is not located at the station position. The signalling push button 4 over conanswering key N at the room station, is indivdual to station 404 and extends to one of the rectifiers l2, located in the power conductor H4 which is common to all stations ending in the digit 4 to the master station. Answering conductor 404a extending from answering contact [1 of key II is connected to a conductor |6a which is common to all stations on the fourth floor. Conductor lSa, in common with similar conductors ltb, I60 and the like leading from the other floors are all connected to the return conductor It in the power unit.

The system of Figure 4 has the advantage of simplified room stations and the location of the rectifiers and transformers in a service room where they can be readily checked and serviced at any time without disturbing the room occu pants. This is of particular value in hospitals and similar institutions.

Since the operation of the system of Figure 4 is similar to that of Figure 1, it is not believed necessary to describe it in further detail.

It will be seen that a selective electric signaling system has been provided in accordance with the present invention in which the number of conductors required have been greatly reduced Without limiting the functioning of the system.

One of the greatest advantages of the system unit 410 and hence over a:

the building where the resides in the greatly reduced switchboardarea required. In the past such switchboards have often required so much space that itv was necessary for the operator to get up from her seat. and walk to the desired switchboard location to insert the calling plug, often being required to, reach way above her head for high positions. This greatly reduced the number of calls, an operator could handle efiiciently. and thereby produced resultant delays and unsatisfactory service. The bulk of wires leading to the switchboard also occupied excessive valuable space and complicated the problem of installing the wiring and switchboard, as well as their maintenance.

Prior master stations have often required a, switchboard area, eight feethigh and eight feet or more wide to serve 1000 rooms due to the bulk, of wire terminals behind the board and the area of the equipment on the face of the board. A cabinet embodying the master station for a1000- room system arranged according to the present invention need be only 6 inches high and loinches. wide. Where the dial system in used it may be even smaller.

It is thus possible, by providing a fiexiblecable. carrying the conductors leading to. the master station, to mount it on a portable stand or cart. which can be placed at the location most con.- Venient for the reach of the operator. Thus itv may be mounted beside an outside telephone switchboard so as to be readily accessible by. the regular telephone operator. When desired it may be moved beside a desk for operation by a secretary during less busy periods.

It is also contemplated that the master station may be incorporated in a narrow switchboard of. the same height as a conventional outgoing-telee phone switchboard so as to be placed beside the telephone switchboard and in effect, be made a. part of it.

Moreover it is possible with the system to locate the master station at a remote point while achieving economy of wiring. The servicing of the system is also simplified by the present invention.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A selective electric signaling system comprising in combination a plurality of groups of electric signaling devices, a source of electric current, a first series of conductors, each conductor of which is individual to one of said groups, a second series of conductors, each of which is connected to at least one of said devices in each group, each of said signaling devices being connected between the member of the first series of conductors which is individual to its respective group and a member of said second series of conductors, switching devices for selectively connecting one terminal of said source to any one of said first series of conductors and for connecting the other terminal of said source to any one of said second series of conductors, a rectifier connected in series with each of said signaling devices, an electroresponsive device connected in series with each member of one of said series of conductors, a call-indicating signal device controlled by each of said electroresponsive devices, a second electro-responsive device connected to each member of said one series of conductors, the call-indicating signal being controlled by each said first-mentioned electroresponsive devices by the corresponding second electroresponsive device to return the signal to normal, and a plurality of energizing circuits for each of said second devices, each energizing circuit including a source of electric energy, manually-controlled contacts at an individual station and at one of said series of conductors.

2. A selective electric signaling system comprising a master station and a plurality of groups of room-call stations, an electric signaling device at each of said room-call stations, a rectifier in series with each of said signaling devices, a first series of conductors each connecting said master station with one terminal of the signaling devices at all of the room-call stations of one of said groups, a second series of conductors each connecting said master station with the other terminal of the signaling devices at one of said room-call stations in each of said groups, a source of electric energy, manually-controlled switching devices at said master station for connecting one terminal of said source to any selected member of said first series of conductors and for connecting the other terminal of said source to any selected member of said second series of conductors, a plurality of call-indicating signal devices located at said master station, and electroresponsive devices connected in series with each of one of said series of conductors, said call-indicating signal devices being respectively controlled by said electroresponsive devices to indicate the sending of a calling signal from said master station, a second series of electroresponsive devices, said second electroresponsive devices restorin said call-indicating signal devices respectively to non-indicating condition, a manual signaling switch at each of said room-call stations, 2. second source of electric energy, each of said manual signaling switches being connected between one terminal of said second source and a member of said one series of conductors, said second electroresponsive devices being connected respectively betweenmembers of said one series of conductors and the other terminal of said second source of energy, and a rectifier in series with each of said seconddevices.

3. A selective electric signaling system comprising a master station and a plurality of groups of room-call stations, an audible electric signal ing device at each of said room stations, a rectifier in series with each of said signaling devices between the terminals of said room stations, a first series of conductors each connecting said master station with a first terminal of all of the room-call stations of one of said groups, a second series of conductors, each connectin said master station with a second terminal of one of said room stations in each of said groups, a source of alternating current energy, a switchboard plug having a contact connected to one terminal of said source, a plurality of switchboard jacks, each having a contact for cooperative engagement with said plug contact, said jack contacts being connected respectively to said first conductors, a plurality of push button switches each connected between the other terminal of said source and one of said second conductors, said system also comprising a series of relays each having a first winding for closing a pair of relay contacts and a second winding for opening said contacts, a series of switchboard lamps and energizing circuits therefor controlled respectively by said relay contacts, the first of said relay windings being connected respectively in series with said first series of conductors, a rectifier in series with the sound of each of said; windings, a second source of alternating current energy, each of said series combination of second windings and rectifier being connected between the first terminal of said second source and the conductor to which its associated first winding is connected, an answering switch at each of said room stations having a common contact being connected to said first terminal of said room station and said back contact being connected to the second terminal of said station through said audible signaling device, said front contact being connected to the second terminal of said second source of alternating current energy.

4. A selective electric signaling system comprising a master station and a plurality of groups of room-call stations, an audible electric signaling device at each of said room stations, a rectifier in series with each of said signaling devices be tween the terminals of said room stations, a first. series of conductors each connecting said masterstation with a first terminal of all of the roomcall stations of one of said groups, a second series of conductors, each connecting said master station with a second terminal of one of said room stations in each of said groups, a source of alternating current energy, a switchboard plug having a contact connected to one terminal of said source, a plurality of switchboard jacks, each having a contact for cooperative engagement with said plug contact, said jack contacts being connected respectively to said first conductors, a plurality of push button switches each connected between the other terminal of said source and one of said second conductors, said system also comprising a return-call check signal device at said master station and a second source of alterhating current energy connected in series there with, and a series of rectifiers, each of said rectifiers being connected between one of said jack contacts and one terminal of the series arrangement of said return-call signal and said second source of alternating current energy, an answering switch at each of said room stations having a common contact and a back and a front contact, said common contact being connected to said first terminal of said room stations and said back contact being connected to the second terminal of said station through said audible signaling device, said front contact being connected to the second terminal of said series arrangement of return-call signal and second source of alternating current energy.

5. A selective electric signaling system comprising a master station and a plurality of groups oi room-call stations, an audible electric signaling device at each of said room stations and a rectifier in series with each of said signalling devices between the terminals of said room station, a first series of conductors, each connecting said master station with a first terminal of all of the room-call stations of one of said groups, a second series of conductors, each connecting said master station with a second terminal of one of said room stations in each of said groups, a source of alternating current energy, a stepping switch and a manual dial circuit for advancing the same, the stepping switch having a movable contact arm connected to one terminal of said source and a series of stationary contacts for cooperation therewith and connected respectively to said first conductors, a plurality of push button switches, each connected between the other terminal of said source and one of said second conductors, a series 13 of relays, each having a first winding for closing a pair of relay contacts and a second winding for opening said contacts, a series of indicating lamps and energizing circuits therefor controlled respectively by said relay contacts, the first of said relay windings being connected respectively in series with said first series of conductors, a rectifier in series with the second of each of said Windings, a second source of alternating current energy, each of said series combination of second Winding and rectifier being connected between a first terminal of said second source of alternating current energy and the conductors to which its associated first winding is connected, an answering switch at each of said room stations having a common contact and a back and front contact, said common contact being connected to said first terminal of said room station and said back contact being connected to the second terminal of said station through said audible signaling device,

said front contact being connected to the second terminal of said second source of alternating current energy.

EDWARD S. RUTH.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the

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