US2371311A - Station selection system - Google Patents

Description

Mardi 13, 1945. L, POTTS 2,371,311

STATION SELECTION SYSTEM Filed Feb. 1-. mil 2 Sheets-Sheet 1 JINVENTOR.

e4 LOUIS 11.1 0115 42 v BY TrbRNEY.

March 13, 1945. M. Po'rTs 2,371,311

- STATION SELECTION SYSTEM Filed Feb. 1, 1941 2 Sheets-Sheet 2 K FIG. 4

' INVENTOR. LOUIS u. POTTS ATTORNEY.

Patented Mar. 13, 1945 STATION SELECTION SYSTEM t Louis M. Potts, Evanston, Ill., assignor to Teletype Corporation, Chicago, 111., a corporation of Delaware 7 Claims.

The present invention relates to station selection systems and more particularly toprinting telegraph switching systems for interconnecting stations for telegraphic communication.

The principal object of the present inventionresides in the provision of station selecting mechanism for use in conjunction with start-stop telegraph systems which will produce impulses that can be repeated by telegraph repeating apparatus satisfactorily and which will effectively serve to operate conventional types of equipment for se lecting any one of a plurality of stations.

The use of station selection methods by means of manual dial equipment is equally desirable in printing telegraphy as it is telephony. From a convenience and utility viewpoint it is proposed in accordance with the present improvement to so regulate standard dial apparatus by means of telegraphic regulating and'periodicity safeguarding equipment as to make its use in conjunction with start-stop telegraphic systems equally practical. Toward this end a mechanical tie-up is effected between thedial apparatus and a startstop regulated shaft of a keyboard transmitter whereby a station selecting dial of standard construction as known in telephony is utilized for generating a. number of permutation code signals which are composed of but a single line change characteristic during the entirety of the code combination so as to reproduce a number of similar signal impulses which may thereafter be used to operate station selecting switches after the manner of standard telephone practice.

In carrying out this plan of operation, the permutation code signal for the letter M has been chosen because it is composed of three successive spacing impulses followed by four successive marking impulses simulating thereby an average length of dialing impulse for operating a station selection switch. Since start-stop apparatus is, in fact, employed for the purpose of generating these dial type signals with the dial equipment serving only as a means of initiating the start-stop equipment and determining the number of signals, there is in effect produced a step-by-step pattern of signal which'is also in fact a start-stop signal and may therefore be received by start-stop apparatus such. as tape transmitters, regenerative repeaters, etc., without impairment or need for auxiliary apparatus to insure against improper responses.

In attaining the above andother objects of the present invention, the principal embodiment described hereinafter utilizes a rotary dial mech-- anism operatively associated with a standard embodiment ofstart stop permutation code transmitting keyboard. The dial may be operated manually by means of rotating a disc which is advanced by a finger movement until a predetermined mark or fingerhole thereof attains a stop.

Application February 1, 1941, Serial No. 376,962

The disc is thereafter released and automatically responsive mechanismrestores the disc to its normal position one step at a time. I As each step is completed, and since a particular key lever of the transmitting keyboard is held depressed during such operation, there is obtained the transmission of a number of character M signals corresponding to the selecting index numeral which was dialed. Thus, if a destination selecting index is comprised of, say, six impulses the particular key leverand the transmitting apparatus are accordingly operated causing to be generated six permutation code signals of a particular letter, which accordingly constitute that number ofstation selecting impulses in succession. These impulses are received at a central station whereat they are elfective to operate selecting switches to select an ultimate destination line over which start-stop messages may then be transmitted to a destination station.

The keyboard mechanism at each subscriber station is of standard arrangement and one of its character keys is depressed for a period of time commensurate with the degree of rotation of the calling dial at the same time the transmitter clutch is engaged for a corresponding number of cycles and as each character code is transmitted the dial is stepped back toward zero position. When the station calling dial reaches its zero position the transmitter is, declutched, the key which had been held down is permitted to resume its normal condition, and the transmission of code signals is arrested. Accordingly, it will be understood that the number of call signals generated through the intermediation of the keyboard mechanism will correspond with the angular position to which the calling dial is rotated and from which the calling dial is returned to its zero position.

For a more comprehensive understanding of the present invention reference may be had to the accompanying drawings and to the detailed specification following hereinafter wherein like reference characters designate corresponding parts throughout and wherein,

-,Fig. l is a circuit diagram featuring the central station equipment for selecting a destination station by apparatus embodying the present invention;

Fig. 2 is a fragmentary front elevation of a start-stop signaling "system keyboard apparatus having applied thereto a station selecting dial according to the present invention;

Fig. 3 is a plan view of the apparatus illustrated in Fig. 2;

L Fig. 4 is a side elevation of the apparatus illustrated in Fig. 2; 4

Fig. 5 is a'detailed rear elevation of the rotary dial mechanism according to the present invention;

Fig. 6 is a timing diagram illustrating typical signal curves of start-stop permutation code signals, and

Fig. '7 is a perspective diagram of certain operating members which relate to the present invention shown separate from the telegraph keyboard.

In the accompanying drawings the reference character II denotes generally a rotary dial type of station selecting switch. Essentially this unit is comprised of a disc [2 which i integrally associated with a stub shaft I3, Fig. 4, and is provided with the ten finger tip receiving apertures, one

representing each numerical integer of the deci .mal series.

Shaft I3 is journaled in 1a bushing 14 which in turn is secured within a central opening of an en-..

closure case I5, the latter'membenas best viewed in Figs. 3 and 4, being supported in an inclined position by means of asuitable supporting bracket [6. Within the case 15, shaft [3 carries integrally associated with it a ratchet wheel ll having teeth which correspond in number and disposition to the finger engagement openings 51 f the finger wheel 12.

' As with conventional telephone dials, the unit I! is provided with a finger stop I8. The latter member is here formed of an armextension originating from lever 19 that is rotatably supported upon said shaft l3. Stop I8 is rotatable through a slight angular distance as determined by the limiting pins 2i and 22 against theformer of which said stop I8 is urged by a spring 23. Integral with lever l9 are two cars indicated 24 and 25, Fig. 5, the latter of which pivotally supports a pawl lever 26 as at pivot 21 and the former of which provides an anchor point for a spring 28 the other end of which is hooked as at 29 to the uppermost extremity of said pawl lever 26.

Pawl lever 26 is limited in its counterclockwise rotation about pivot 21 as urged by the afore-described spring 28 when-its uppermost extremity encounters the stop lug 3| which in turn may also be integrally formed with the aforedescribed lever l9. Upon the rotation, of lever l9 as when its finger stop extremity I8 is engaged duringv the final degrees of movement of finger wheel [2, pawl lever 26 will be moved bodily upward with pivot 21 advancing in a counterclockwisev direction asviewed in Fig.5 so that tooth 32 of pawl lever 26, the upper .edge of which isinclined as indicated in Fig.- 5, encounters the extremity 33 of a bell crank lever 35, Fig. 4, there will result .the clockwise rotation of said pawl lever 26 about its pivot 27 and in opposition to the return spring 28 as it accordingly yields to the extending portion 33 of hell crank lever 35.

Reiterating, the finger wheel I2 is operated by inserting a finger into one or the dial openings !v which is opposite a numerical digit'corresponding to an identifying character of the station sought, and the finger wheel isrotated in a clockwise direction as viewed in Figs. 2 and3,.counter clockwise as viewed in Figs. 5 and 7. This movement causes disc l2 and ratchet wheel I! to beIconcurrently displaced to a significant angular position as detent arm'34 ridesove'r a corresponding number of teeth iniatch'e't wheel l1, indicativeof the digit thus operated. The finger upon encounter -ing stop piece I8 moves the latter member a distance corresponding to the space between. stop pins 2| and 22 and the finger I is withdrawn. {thereupon lever. l9, being. under tension: of issies iis e rrdeset ea endeavors to return to its original position as illustrated in the drawings and in so doing, pawl 26 is carried downwardly causing its tooth projection 32 to engage the extremity 33 of bell crank. 35 and to. rock the latter in a counterclockwise direction, Fig. 4, about its pivot 36 which motion is mildly resisted by the lever return-spring 31. Pawl 26 continues to engage extremity 33 thereby holding lever 3335 in its counterclockwise position (as viewed in Figs. 4 and 7) until arm 61, integral with ratchet I1, re-

: turns to cooperate with projection 68 to disengage pawl 26 from extremity 33, as will hereinafter appear.

The movement on the part of bell crank 35 is then immediately translated into a counterclockwise motion of the character M operating bail 38, Figs. 2, 4, and '7. As bail 38 is rocked in a counterclockwise direction, Fig. 2, its light acting return spring 39 becomes distended and its remote extremity 4| engages and depresses key lever 42 whereby there is generated, through the normal operation or the transmitter mechanism, a permutation code signal corresponding to the character M as this key lever is identified, Fig. 3.

A keyboard apparatu for transmitting signals of the type illustrated-in curve A of Fig. 6 is more fully described and explained in U. S. Patent 1,595,472. For the purpose of explaining the application of the instant invention, it will sui'fice to state that upon the operation of any one of the key levers such as the particular key lever M indicated by the reference character 42, there is conditioned a set of five code bars each one of which supervises the performance of an associated goose-neck lever 43, Fig. 2, while also as a result of the operation of any one of said set of key levers there is affected a leftward movement on the part of common release bar 44, Fig. 4, the rotation of a trip lever 45, and ultimately the release of a declutching element 46. In consequence of the release motion on the part of lever 46, clutch elements 4'! and 48 are brought together so that .set of goose-necks 43 each of which in turn controls an individual pair of contacts of a series which are arranged in a parallel alignment, In addition to this utility, however, cam sleeve 49 in accordance with the instant invention performs a further purpose as will now be described.

One of the cams of assembly 49 has been especially indicated 5|. Against the periphery of this cam there rides a follower roller 52 which, as best indicated. in Fig. 2, is carried by one arm 53 of abell crank member whose other arm. 54 is pivotally connected to apawl. 55, the extremity of which is indicated 56 in Fig. 5. f

In consequence of the afore-described arrangement, as cam 5| is rotated, there results a horizontal reciprocation of pawl 55 which, with' its extremity 56 engages consecutively the teeth of ratchet wheel l1 causing the latter member to be-rotated in a clockwise direction, as viewed in Figs. 5 and '7 (counterclockwise asviewed in Figs. 2 and 3) one step at a time. each impulse or character M signalis transmitted during the rotation of. cam assembly 49, so also by reason of the horizontal actuation of pawl 55 and through its engagement with ratchet wheel l1, there is effected a restoration of the finger wheel 12 one step at a, time until the normal or zero position is resumed.

It will be recalled that finger wheel 12 when rotated in a clockwise direction as viewed in Figs. 2 and 3 is capable of a total movement corre sponding to a certain number of composite digit movements each equal angularly to the distance between successive finger holes 51 of which there are ten in the conventional type of dial illustrated and that the final degree of movement of any station selecting operation results, in addi: tion to the rotation of finger wheel l2, in the movement of finger stop 18 through a limited distance as represented by the two stop pins2'l and- 22. When the operators finger is withdrawn, finger stop [8 being urged by the return spring 23 immediately seeks to resume the position as indicated in Fig. 5 whereat it rests against the stop pin 2|. It is to be noted that during the operation of linger stop member I8 when it'was rotated counterclockwise (Fig. 5) pawl 32 through its articulation at pivot 2'1 with an ear 25 which is integral with arm I9 is caused to be moved upwardly until its shoulder portion 32 overtakes the extremity 33 of bell crank lever 35. In passing over this extremity spring 28 yields sufficiently to permit said pawl 26 a slight clockwise movement about pivot 21 but after its shoulder 32 comes into the clear again pat/13126 resumes its relative position to arm H! as {indicated and shoulder 32 is placed above said extremity 33 of bell crank 35 awaiting the release of finger piece 18. As a result of the influence of spring 23, when the operators finger is removed, the entire assembly including arm l9 and pawl 25 are rotated clockwise, Fig. 5, as before stated. Shoulder of pawl 32 now positively engages the extremity 33 of hell crank lever 35 and causes the latter member to be rocked counterclockwise about its pivot 36 as viewed in Fig. 4. Presently stop arm l9 encounters the limit pin 2| and {its movement is thereat arrested determining thereby the extent of rotation of bell crank 35 which rotation is opposed by the return spring 3'1. In consequence of the counterclockwise rotation (Fig. 4) of hell crank member 33-35 its farthest extremity which underlies one arm 64 of the bail lever 38 causes said arm to be raised against the tendency of a return spring 39, Fig. 2, effecting the depression of its key-lever actuating extremity M as well as the rotation of its transverse bail portion 59. At the end of bail portion59 uppermost in Fig. 3 there is integrally formed a trip arm 6i which carries the adjustable screw 62 for engaging the horizontally extending lug 63 as indicated also in Fig. 4. I

In consequence of the operation of lever 38 there are efiected two results. Firstly, key lever 42 is depressed, effectively reproducing the main ual actuation for transmitting the alphabetical character M and secondly the clutch trip dtf'fis rotated which results in the release of spring actuated driven clutch member 48 so that, it comes into engagement with clutch driving member 41.

In accordance with the conventional operation of keyboard telegraph transmitting appater signal. In other words, to eiTect the transmission of a number of character signals it is necessary to depress any key lever and to permit the same to resume its normal position a number of times corresponding to the number of signals to be transmitted. This safeguard is usually obtained by the provision of a trip release mechanism in connection with clutch 47-48.

It is now proposed by providing the extension SI of bail 38 and by withdrawing clutch trip 46 at the same time that key lever 42 is depressed to permit cam assembly 49 to rotate a number of revolutions corresponding to the number of character M signals which aredesired. i

As cam assembly 49-efiects one revolution after another its-cam 5|, Fig. 2, encounters follower roller 52 and rotates bell crank 53 clockwise in opposition to its return spring 66, and as these operations proceed successively the downwardly extending arm 54 of said bell crank causes the pawl 55 to be reciprocated to and fro. With each rightward movement of pawl 55, Fig. 7, leftward as viewed in Figs. 2 and 3, a succeeding tooth of ratchet wheel I! is engaged and then pulled forward thereby causing the finger wheel l2 to be restored by clockwise rotation, Figs. 5 and 7.

When the normal or zero position of finger wheel I2 is ultimately attained arm 61 which is carried integrally with ratchet wheel I! engages the projection 88 of pawl 26 causing the latter member to be rotated clockwise about its pivot 21 and in opposition to its spring 28. This movement withdraws shoulder 32 from the extremity 33 of hell crank lever 33--35 permitting the lat ter member under the influence of its restoration spring 31 to resume its normal position as indicated in Fig. 4. In consequence bail 38 is free to resume its normal position under the influence of spring 39 whereupon bail extremity 4| is withdrawn from ke lever 42 and extremity BI is withdrawn from the horizontal plate 63 of clutch trip 46.

In this manner there is effectively reproduced, by the use of a telephone station calling finger wheel l2, a system of transmitting a number of permutation code character M signals corresponding to the call number of impulses in a station selecting signal. As the station selecting signals emanate from the transmitter apparatus,

generally indicated 68 in Fig, 1, they may, before arriving at the central ofiice 69, be regenerated at a repeating station such as the one indicated H, Typical repeating station apparatus is illustrated in U. S. Patent 2,104,273 and since the station selecting impulses are, in fact, a number of similar start-stop permutation code signals issued in series, they may be repeated over conventional start-stop apparatus such as illustrated in this disclosure without distortion.

Attention is directedto curves B and C of Fig. 6, where there is shown respectively the minimum and maximum peak or tolerance characteristics of a dial signaling equipment such as is conventionally employed in telephony. Test observations have indicated that any dialing signal having a spacing characteristic smaller than that indicated in curve B or one larger than that indicated in curve C is likely to produce false responses in station selecting switches of this type. Accordingly, and since five unit permutation code signals of the type illustrated by the curve A are reeeivablein standard telegraph .equipment, 'it has been found expedient to utilizea particular code combination which in accordance with convention has been assigned to the alphabetical character -M which signal is indicated by the curve D to be utilized in the purpose of reproducing station selecting impulses of the type necessary in operating telephone switching equipment. The spacing characteristic of the code combination for letter M will, as may be noted by comparing curve D with curves B and C, constitute a spacing impulse greater in length than the minimum curve B and yet one which is less than the maximum impulse curve C. In composing the station selecting impulse of three code impulses contiguously arranged including the start impulse, it may be noted that a total length of spacingcurrent, somewhat in excess of a median signal length, is thereby obtained. By observing curve D in comparison with curves B and C one may notice that a two code impulse signal, which corresponds according to custom with the code combination for the character V, is also usable as a station selectingv switch operating impulse if preferred. I

There will now be described briefly the circuit of Fig. l to illustrate the application of the present invention in the embodiment discussed above comprising a central station and a limited number of outlying stations. The reference character 68 designates a transmitting station which may be a unitary apparatus of the type illustrated in U. S. Patent 1,632,297 or of the type illustrated in U. S. Patent 2,177,077. This outlying station in addressing the central ofilce I59 may transmit its signals over a line in which is located a repeater apparatus II which may be of the type shown in U. S. Patent 2,105,173 or of the type shown in U. S. Patent 2,104,273. Either of these classes of repeater apparatus partakes of the characteristic of signal regenerative repeater, that is, signals received from the outlying station 60 are duplicated and retransmitted from a battery local to the regenerating station II and in this manner distortion efi'ects caused by conditions inherent in the line are eliminated by a well-known practice of reconstructing the original signals under the control of the transmitter 68 so that as the enter upon the succeeding line directed to the central station the true theoretical signal pattern is again produced.

At the central station the incoming line passes through the winding of a slow-to-release relay I2, thence over local line 14, contactor I3 and its normal make contact point 15, through the winding of relay I6, to ground. As aresult of normal marking current on the line, relay 12 will become energized and remain in its attracted condition notwithstanding the signal interruptions due to the succession of line selecting im-' pulses comprised of a series of character M code combination signals, but relay "IE will intermittently release and attract its armature 11 causing the latter element to be actuated from itsfront contact point19. toward its back contactpoint I8 andvice versa.

As a result of the energization of slow-to-release relay 12 there will be drawn up its armatures SI and 82, the former receding from its back contact point 83 and engaging its front contact point 84, while the latter will be attracted to its sole front contact. As a result of the closure of armature82 with its front contact a circuit will be established tor operating the station selecting switch mag n et 86, traceable from grounded front contact .poin-t19 of relay-l8 through armature", conductor. 81, armature .82,

its front contact of relay [2 which is normally energized, conductor 88 to'the junction point 89, conductor 9I, winding of magnet 86 to grounded battery at 92.

As a result of the operation of magnet 86 intermittently under the control of received signals the station selecting switch will be rotated in a step by step manner advancing the three wiper brushes 93, 94, and so that they successively engage the contact points 96, 91, and 98, respectively, after the manner of station selecting switch operation-more thoroughly explained in Kempster B. Millers book of American Tele phone Practice, fourth edition, chapter XXXIV, published 1905.

As operating magnet 86 is alternately energized and de-energized in response to the fluctuations of armature 11, the station selecting switch will advance its above recited wiper brushes until they attain'a position corresponding to the number of station selecting impulses received, whereupon the station selecting switch will momentarily come. to rest with one of the contact points 98' engaged by its wiper 95 for a period sufliciently long to cause the operation of slow-to-operate magnet 99. This is traceable over an obvious circuit from grounded, battery IIlI winding of slow-to-operate relay 99, line I02, wiper 95 and a particular one of its contact points 98, to the, grounded bridging circuit I03. As a result of the operation of relay 99 its two armatures I04 and I05 will be attracted, the former coming into engagement with the contact point of contactor I3 and establishing a circuit for connecting the incoming line to the destination station, at the same time withdrawing contactor 13 from contact point 15 after the well-known manner of make before break switch operation.

Contactor I05 engaging contact point I06 completes a circuit for maintaining energized the station selecting operating magnet 86. This circuit is traceable from grounded battery 92, through the winding of rotary switch operating magnet 86, conductor 9| to the junction point 89, thenceover conductor 88,. front contact of armature-82, conductor 8'1, armature 11, (which is now released) contact point 18, contact point I06 and its aramature I 05 (which is now at: tracted) conductor I08, contact point 84 to grounded armature 8| (which is still attracted because normally current is flowing in the line). When contactor I3 is withdrawn from contact point I5 as above described there results the deenergization of relay I6. As a result of the attraction of armature I04 with the contact point of contactor l3 incoming line through the winding of relay 12 and local conductor 14 is continued over the contact point of contactor 13 and its associated armature I04, conductor I09, wiper 98 and one of its contact points corresponding to the selected station, thence out over one of the line conductors III- to a particular destination station II2;, IIZA, etc.

, After the communicationwith the destination station II2, II2A,'etc., has been-com-pleted,-the line conductor may be broken at-any pointeither between the central-station and one of the destination stations or between the calling station 68 and the central station, and the apparatus will become restored to zero or normal condition in the following manner. Slow-to-release relayTlZ, being in;ci1-cu it at all times,.when,the current is interrupted fora sufiicient'len'gth oiftir'ne to dee nergize -s'aid relay' its arm'atures 81 and82.wil l bepermitted to fall back removing ground at ar ground will be introduced again to the circuit including winding of magnet 86 as follows: from grounded battery 92, through the winding of magnet 86, conductor 9|, armature H3 and contact point H4, conductor I 15 to the bridging circuit of the several contact points 91 and wiper 94, thence conductor H6 contact point 83 to grounded armature 8|. As a result magnet 86 will become energized again attracting its armature H3 away from contact point H4 whereupon the circuit will again be broken for said magnet 86 which will again release its armature I I3, etc., the operation continuing intermittently until wiper 94 resumes the normal position at which it engages the zero contact point H'I-which does not connect with conductor H5. Since magnet 85 operates all of the wipers 93 to 95, inclusive, there will in this manner be efiected the restoration of the switch to normal or Zero condition in readiness for a succeeding station selection operation.

In illustrating the application of the present invention there has been chosen for arbitrary illustration the rotary line finder apparatus identified as Strowger step-by-step switches. To those acquainted with exchange office apparatus it will be evident that other forms of line finder systems, such as the panel or cross-bar selectors,

are equally adaptable for use and that multiple digit selection may be obtained by the application of known circuit arrangements.

While the present invention has been explained and described with reference to but a single embodiment, it is to be understood nevertheless that numerous variations and modifications may be incorporated without substantial departure from the present invention. Accordingly, it is not intended to be limited to the specific details of the foregoing specification nor to the particulars of the accompanying drawings except as indicated in the hereunto appended claims.

What is claimed is: 1. In a telegraph station selection system, a

central office comprising a selector switch, intermittent-signal. controlled means for actuating said selector switch, a plurality of outlying stations, a telegraph keyboard transmitter at each outlying station, and a dial apparatus also at each outlying station for automatically actuating said keyboard transmitter for producing step-bystep digital signals to actuate said selector switch to select, for communication with a calling outlying station, any other of said plurality of outlying stations.

2. In .a telegraph station selection system, a central oflice comprisinga selector switch, stepby-step mechanism for operating said selector switch, a plurality of outlying stations, a telegraph keyboard transmitter at said outlying stations for producing intelligence signals, and a dial, apparatus also at each outlying station for automatically actuating said keyboard transmitter to generate a succession of intelligence signal impulses under a single manipulation of said dial apparatus to actuate said step-by-ste mechanism of said selector switch for stablishing communication with one of said outlying stations.

3. In a telegraph system, a central station, a

mature 8| from the circuit which had been holdplurality of outlying stations, telegraph apparatus at each of said outlying stations for sending and receiving start-stop equal length permutation code signals, switching means at said central station for establishing communication automatically between two of said plurality of outlying stations under the control of step-by-step signals, and dial apparatus at each of said outlying stations responsive to a single manipulative action for automatically actuating said telegraph apparatus forgenerating a plurality of groups of said equal length code signals to operate said switching means step-by-step.

4. In a telegraph communication system, a central station, a plurality of outlying stations, telegraph apparatus at each of said outlying stations for sending and/or receiving start-stop equal length permutation code signals, switching means at said central station controllable by any calling one of said plurality of outlying stations for establishing communication automatically with another one of said plurality of outlying stations under operation by. step-by-step signals,

and dial apparatus at each of said outlying stations responsive to a single manipulative operation for automatically actuating said telegraph apparatus for generating predeterminedly said equal length permutation code signals to operate step by step said switching means.

, 5. In a telegraph system, a central ofiice, a plurality of subscriber stations, line conductors connecting said stations with said office, communication apparatus including a set of telegraph key levers at each said subscriber stations, means associated with each of said communication apparatuses including. a dialing device for selectively actuating one of said telegraph key levers automatically for transmitting from said subscribers station over its line conductor a series of equal length permutation code impulses to said central station, and means at said central'station responsive to said series of equal length permutation code impulses for establishing a connection with another'line conductor extending therefrom. I

6. In an intercommunication system, an exchange station, a plurality ofsubscriber stations, line conductors connecting said subscribers stations with said exchange station, selector switch equipment at said exchange station, a telegraph I keyboard transmitter at each of said subscriber stations, and a dial apparatus also at each of said subscriber stations for automatically actuating said keyboard transmitter to generate impulses to operate said selector switch equipment at said exchange station and establish a connection with another line conductor extending therefrom.

7. In a telegraph system, a plurality of printing telegraph stations, telegraph signal transmitters at each of said stations, a central ofiice, line conductors extending from said central office to said telegraph stations, selecting apparatus at said central ofi'ice for automatically selecting the line conductor of one of said plurality of stations for communication, and means for controlling said-selecting apparatus including a calling dial at each of said plurality of stations, and equipment interconnected with said dial for actuating said telegraph signal transmitter to generate a number of signals in accordance with the degree of rotation of said dial.

LOUIS M. POTTS.

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