US2289746A - Teletypewriter "answer back" circuit - Google Patents

Description

"ANSWER BACK CIRCUIT Filed. Mapch 26, 1940 M 55 P x 4 I On lfl n1 A 2 M w e 7 P RI- 0 v. mm Mm 5 5 U m H n. p. R J M 6 L4 0. U 5. I, H5 T INVENTOR W M BACON BY M i A TORNEY Patented July 14, 1942 TELETYPEWRITER ANSWER BACK CIRCUIT Walter M. Bacon, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 26, 1940, Serial No. 325,942

8 Claims.

This invention pertains to teletypewriter switching systems and more particularly to an improvement over known arrangements for automatically transmitting a series of code signal trains from a telegraph station to form successive symbols in a fixed message. These signal trains may be transmitted from a called telegraph station in response to, the reception of a teletypewriter signal from a teletypewriter station with which the called station is connected.

In the operation of communication systems, various services are provided, such as the socalled time of day, weather reports, holiday message, test sentence, answer back and numerous others, wherein the subject-matter of the messages transmitted remains unchanged for considerable periods. In the case of certain of these messages, it is necessary to change the subject-matter from time to time.

When such service is provided in teletypewriter systems, various apparatus has been used for setting up the codes of the characters to be transmitted. In many cases cams have been cut so as to actuate the signaling contacts in the desired manner. In other cases, a continuous tape has been used.

It is an object of the invention herein to improve the apparatus used in teletypewriter systems for the automatic transmission of a fixed message.

It is a further object of the invention herein to reduce the cost of and to increase the flexibility of the apparatus used for automatically transmitting a fixed message in a teletypewriter system.

A feature of this invention is the adaptation of a well-known, inexpensive, and widely used multibank,'rotary selector switch to set upsuccessively, by means of its brushes and banks, the elements constituting the signal trains forming the successive characters of the fixed message to be automatically transmitted.

Although in the disclosure hereunder a teletypewriter transmitter is used in conjunction with the rotary switch, the teletypewriter plays no part in setting up the code of the characters. The function of the teletypewriter as used herein is to control the timing of the transmitted signals and to transmit the start and stop impulses at the beginning and ending of each character train. It is not necessary to use a teletypewriter to do this as the function may be performed by any of a number of other machines, such as a transmitting distributor, or, in general, any device which will transmit a start signal together with the train of impulses set up on the selector as shown herein and a stop impulse in the proper sequence and with the proper timing, so as to cooperate satisfactorily with the receiving mechanism with which it is connected,

Any one skilled in the art will appreciate the flexibility of the proposed arrangement, which requires only strapping or leaving open contacts on five of the banks of a step-by-step selector to form the open or closed elements of the character forming train. When used with a teletypewriter transmitter as shown herein, one side of the station loop is connected to each of five brushes which cooperate with each of the five banks. Certain of the bank terminals on a particular bank are strapped together and connected to one of the five character element contacts on the teletypewriter transmitter. Other bank terminals are left unwired. Each of the five teletypewriter contacts which ordinarily transmit the character forming signal elements is closed in turn, so that each is positioned to transmit only a marking signal element. When the corresponding selector brush is in engagement with a strapped bank terminal, the path betweenthe two loop conductors through the selector brush and bank is closed and a marking signal element is transmitted. If the corresponding selector brush for a particular teletypewriter transmitting contact is not strapped, the station loop circuit is open during the interval that the selector brush is in circuit and in engagement with the open contact, even though the corresponding teletypewriter transmitting contact which is in circuit is closed. A spacing signal element is transmitted, therefore, when an open bank terminal takes its position in its proper sequence in the path between the two station loop conductors.

The invention herein has been illustrated in connection with an answer back device. In such a device either in response to a particular incoming signal, or upon establishing connections with the called station, a fixed message, for which the transmitting apparatus has been previously arranged, is automatically transmitted to the calling station. The message may, of course, take any form. It may identify the called station. It may transmit a weather forecast, a stock quotation, the time of day or any other subjectmatter.

The invention herein, however, is not limited to answer back arrangements. It may be applied generally to automatically transmit trains of timed impulses each comprising almost any uniform number of elements, each element susceptible of variation to form either of two signals.

Reference to the single figure of the drawing which shows the invention incorporated in a teletypewriter station circuit to provide an answer back device and the following detailed description will provide an explanation of the invention.

The manner in which the answer back circuit operates will now be described in detail.

When direct current battery of the proper polarity is connected to conductor IIJI at the distant central station, the circuit is extended through conductors It! and I62, the top back contact and armature of relay I03, through the winding of relay H34 and the bottom armature and back contact of relay I83 to ground, operating the armature of relay IM to engage its right-hand contact. When the armature of relay IM engages its right-hand contact, a circuit is closed from ground on the lower power supply conductor through conductor I65, the armature and right-hand contact of relay I04, winding of relay H36 and conductor IEJI to the upper power supply conductor, operating relay I08. The operation of relay I85 operates relay I03 over a path from ground-on the lower power supply conductor, conductor I25, winding of relay IE3, bottom front contact and armature of relay I06, over conductor It? to the opposite side of the power supply. The operation of relay I23, by closing its bottom make contact, closes the path through the station circuit to form with conductors IElI and I08, which extend to the central switching station, a continuous closed loop. The operation of relay I53 also breaks the path through conductor I62 to ground heretofore traced by opening its top back contact. That part of the loop circuit included in the normal telegraph signal path through the station may now be traced over conductor IilI, through conductor I39, contact IIEl, (to be described in more detail herein) conductor II'I, through the station break key and selector magnet, relay I04 winding, bottom armature and front contact of relay I93 and resistance IIZ to conductor I28. When the station loop is established, relay IM releases, as the polarity of the battery connected to its winding is changed at the central station in a well-known manner.

The operation of relay IIJB also closed the power circuit to drive the teletypewriter motor. This circuit extends from ground on one side of the power supply, through conductor N3, the teletypewriter motor, through the bottom front contact and armature of relay I06 and conductor IIlI to the opposite side of the power supply. Relay Iflt operated, locks through its top inner armature and make contact, through the middle pole of the station start switch I I4, motor control contacts H and conductor II3 to ground.

The operation of relay I95 also supplies ground through the top pole of switch H4, the top outer make contact of relay IfiIi, conductor H6, switch arm Illa of bank H811. of the answer back selector H9, bank contact IZEIa, conductor I2I and the winding of relay I22 to battery, operating relay I22. The operation of relay I22 closes a path which operates answer back magnet I23, from ground through the top pole of switch II4, top outer front contact and armature of relay I06, bottom armature and front contact of relay I22, through the winding of magnet I23 to battery. The operation of relay I22 at its top armature and front contact closes a short-circuiting p'ath around the teletypewriter signal code transmitting contacts from junction point I26, through conductor I21, top front contact and armature of relay I22 and conductor I28 to junction point I29a to I29e, inclusive.

The teletypewriter transmitter used herein operates according to the Baudot principle in which a train or signal elements is transmitted for each character, each train comprising a spacing or no current pulse, as a start pulse, followed by five elements, each of which may be a current or no current impulse in various combinations according to the particular character to be transmitted and a final current pulse for a stop pulse. When power is connected to the teletypewriter motor, a driving shaft in the teletypewriter is rotated. If any one of the group of character keys of the transmitter is depressed, each of the group of five character element contacts, I33a to I396, inclusive, is operated independently in such manner as to assume either one of two positions. A latch Withdrawn from engagement with the teletypewriter driver shaft, or transmitting shaft as it is otherwise known, permits the driving shaft to rotate the transmitting shaft, by means of a friction clutch, through one revolution. During this single revolution, a closed circuit or an open circuit is established successively through each of contacts IBM to IEIle and bus-bar I3I, dependent upon the position in which each of the contacts has been independently fixed, which in turn is dependent upon the code of the character to be transmitted. This mechanism is well known in the teletypewriter art.

The contacts IID are the contacts on the teletypewriter which close the loop through the station circuit when the teletypewriter transmitter is in the stop position, which is the position assumed when the teletypewriter transmitting shaft is idle, and during the intervals between the transmission of successive characters.

The special teletypewriter station circuit of the invention herein, arranged to transmit a station identifying code, is distinguished parti'cularly by the inclusion in the circuit of (l) the magnet I23 which operates the repeat letters key I25 by means of the armature bail I24 and (2) the selector switch I I9, comprising the switch arms I I Ia to I I If, the switch terminal banks H841 to I581 and the magnet I33 which rotates the switch arms in unison.

Ordinarily in the operation of a teletypewriter station circuit, the selector switch is not used. The station loop is closed through contacts corresponding to contacts Hi} during the stop intervals. When one of the character keys is operated, the contacts corresponding to III) are opened to transmit a start impulse. Then each of contacts ISila to I366, inclusive, is positioned so that the loop through the station circuit is connected through each of these contacts in turn. The loop may be opened or closed by each contact in succession. In the invention herein the opening and closing of the circuit for the transmission of the station identifying code is not performed by contacts I3Iia to little. Instead the selector switch arms and banks are connected individually in series with the transmitting contacts'. The transmitting contacts 532a to I3Ge are positioned successively in series in the circuit and closed. This is performed by automatically operating a particular key by means of a magnet. In this case the repeat letters key I25 is operated by magnet I23. This in turn releases the transmitting shaft I32 and positions all of the contacts IBM to ISiie so that the station loop is closed through each one in turn. Notwithstanding each of the teletypewriter transmitting contacts is closed in its turn, as it takes its position in the station loop circuit due to the operation of the repeat letters key, the station loop circuit may be opened or closed in succession during the transmission of each of the five signal elements comprising the code of a character, dependent upon whether the path connecting loop conductor IOI to loop conductor I08 is opened or closed through the selector brush arm and bank terminal in series with contacts I3lla to I30e, inclusive, at the particular instant.

It may be observed that there are six switch banks, H811 to I I8), inclusive, and but five character contacts I3lla to I3ile. Only five of the six switch banks, II8b to H8 inclusive, are employed in setting up the code of each character of the identifying code. The sixth bank, Him, is used (1) to prevent the transmission of characters until the teletypewriter motor has attained normal speed, which is attained after it has completed eight revolutions; (2) to maintain the answer back magnet energized, so that the repeat letters key will be maintained in a depressed position in turn positioning the character code transmitting contacts I30a to I3fie in series in the station loop circuit and closed while the answer back selector bank is setting up successively the code for the various characters forming the answer back message; (3) to stop the selector switch brushes on the last bank terminals and place the selector under the control of the station power switch I I4.

As the character code transmitting shaft I32 revolves, contacts III] are first opened by means of its associated cam. Contacts I34 are closed. This energizes the switch rotor magnet I33. As is well known, the energizing of rotor magnet I33 does not rotate the switch arms II'Ia to ill This does not occur until the rotor magnet I33 is deenergized. Contacts I34 will remain closed as the transmitting shaft rotates through the positions in which contacts I3Ila to I3Qe, inclusive, are successively closed during part of one revolution. Simultaneously with the reopening of contact I33e, contacts I34 are reopened. This removes ground from the rotor magnet I33, deenergizing it, and steps each of the arms IIIa to II If, inclusive, simultaneously to its next succeeding terminal on its associated selector bank.

The path from ground through the top pole of switch 4, conductor H6, switch arm II'Ia, conductor I2I and the winding of relay I22 is maintained closed while switch arm Illa is in engagement with each of the first eight contacts on bank Him and as it moves progressively between these contacts, so that the short circuit through the top armature and front contact of relay I22 is maintained between conductors WI and I88 around each of the transmitting contacts. The loop through the station is thus maintained closed and no signals are transmitted to the distant station even though the transmitter in the station where the answer back mechanism is located goes through the steps of transmitting a start pulse and five marking pulses on each of the first eight revolutions of the transmitter.

As the transmitting shaft revolves for each cycle, the rotor magnet is energized as contacts I34 close during each start pulse. The rotor magnet is released when contacts I34 are opened simultaneously with the ending of the transmission of the last of the five code elements of each Sages of any length without limitation.

character. The arms 'IIIa' to H1 are moved simultaneously to the next succeeding terminal on their associated banks, I I8a to H8 each time rotor magnet I33 releases. This occurs once each revolution of the transmitting shaft.

After the transmitting shaft has revolved eight times, the teletypewriter motor will have attained the proper speed for the transmission of code signals. The transmission of the character code signals will start on the ninth revolution of the transmission shaft. The six brushes I Ila to I ll inclusive, at that time will each be in engagement with the ninth contact on its respective bank. With brush lI'Ia in engagement with the ninth terminal on bank IIBa, the path through the winding of relay I22 will be brokenand relay I22 will release. This will break the short circuit around the teletypewriter transmitting contacts. The opening of contacts H3 will then be effective to transmit a start impulse and the open or closed circuit which will be established through the ninth terminal of each of banks H112 to III will be effective to transmit a marking or a spacing impulse to comprise the code of the character it is desired to transmit.

When brush arm la is in engagement with the ninth terminal of bank II 8a, a circuit may be traced from ground through the top pole of switch I I4, the top outer front contact and armature of relay I06, switch arm IIIa, ninth terminal of bank II8a, conductor I35, the bottom break contact combination of relay I22, through the winding of magnet I23 to battery. This will hold magnet I23 operated. The bottom contacts of relay I22 are make-before-break contacts. The reason for this is to prevent the deenergization of magnet I23 .when relay I22 releases. The circuit from battery on one side of the magnet I23 winding to ground is transferred from the path directly through the bottom armature of relay I22, to the path through the ninth contact on bank Ba and the bottom make-beforebreak contacts of relay I22 before the path through the bottom armature of relay I22 is broken. This maintains the bail I 24 and the repeat letters key I25 in the depressed position.

Bank terminals 9 to 2|, inclusive, on each of the five banks, H811 to H8 inclusive, are available for the transmittal of code characters. A total of thirteen symbols identifying the called station, or for any other purpose, may be sent. It should be observed that the path through each of the bank terminals of banks H811 to H8), inclusive, between the eighth and twenty-second terminals, may be wired in such manner as to be open or closed so as to send either a marking or a spacing signal element as desired to form the character required.

Although the banks shown have but twenty two terminals each, a bank having more than twenty-two terminals may, of course, be substituted if more than thirteen characters are to be transmitted.

It is, of course, possible to use a number of selectors successively, each arranged with six banks, one bank for control, and five banks for character formation. When the characters set up on the first selector have been transmitted,

control of the transmission of the characters is transferred to the first bank of each of the succeeding selectors in turn and the character code is set upon the five remaining banks. With this arrangement it is possible to transmit mes- If a continuous message is to be sent, it is not necessary to reserve a group of terminals on each bank to permit the transmitter to come up to speed as, once started, the transmitter need not be stopped until the message has been transmitted.

Applicant contemplates the use of his invention, not only as a called station identifying device, but also as a means for transmitting by means of telegraph or teletypewriter signals, predetermined messages set up on the selectors in rotation by means of a clock-controlled switching mechanism to transmit the time of day in response to the reception of a particular character from a distant station.

It may also be used for transmitting any message, such as weather reports, stock market quotations, etc., the selector bank signals being changed from time to time as necessary. To facilitate changing the message which is transmitted in such cases, applicant proposes to terminate all conductors connected to the selectors in flexible terminations such as jacks and plugs for manual change of the transmitted message or in separate selector banks and switches where it is desirable to change the message mechanically, as in time of day service. In this manner a selector switch bank wired in accordance with the new changed message may be readily substituted for a switch bank, the message on I which is no longer to be transmitted.

When brush Illa steps from the twenty-first to the twenty-second terminal of bank IISa the path to ground heretofore traced is opened and magnet I23 releases.

When brush Illa is stepped to the twentysecond terminal of bank I IIla, the circuit may be traced from ground, through the top pole of switch I I4, the top outer make contact and armature of relay Hi6, brush Illa, the twenty-second terminal of bank II8a through the selector rotor magnet to battery. The ground supplied over this path maintains the rotor magnet I33 energized under control of the station start switch H4.

The answer back device remains in this condition under control of the station start switch [I4 until the switch is operated to break the ground connection. This releases the selector rotor magnet which rotates one step, so that one end of each of the double-ended switch arms, Illa to Ill inclusive, engages the first contacts I2Eia to I20 of each of selector banks 8a to H8 The operation of switch H4 by opening the path through the middle pole breaks the holding path for relay I96 which thereupon releases. The engagement of the bottom pole of switch II4 on its cooperating contact I36 closes an obvious power supply circuit for the teletypewriter motor, to replace the path broken at the bottom armature and back contact of relay I36 when relay IE6 releases. Relay I03 is maintained operated after the release of relay me over a path from ground on the lower power supply conductor, through conductor I 65, through the winding of relay I83, through contact I35, the bottom pole of switch I I4 and conductor Illl, to the upper'side of the power source. This maintains the line loop to the central station closed. At the conclusion of communication, switch I I4 is restored to its position as shown on the circuit drawing, so that the cycle of operations described above may be repeated.

As an alternative or as a complementary arrangement for the above, it is possible to provide an answer back arrangement which may be used to check the identity of a station with which a second teletypewriter station is connected while communication between the stations is in progress rather than before it has started. The modification in the above-described arrangement which is necessary in order to perform this is of a ver minor nature. It consists in the provision of the conductor I38 shown connected to junction point I31 in conductor IIB. This conductor may be extended through contacts I39 to ground. Contacts I39 are normally open but are arranged to be closed in any suitable manner on receptions of a designated signal. Ground supplied through contacts I39 under these circumstances takes the place of ground supplied through the top pole of switch H4 and the top front contact and armature of relay ms. The switch II I will have been operated to the down position. Relays I04 and I96 will be released and relay IE3 will be operated. The operation of relay I22, magnet I23, repeat letters key I25, selector II9, contacts II3, contacts Itfia to I3Ile and contacts I34 is the same as described above. Under these circumstances, however, it is not necessary to delay the transmission of character signals as the teletypewriter motor will be operating at full speed. If, therefore, this feature alone is required, all of the bank positions may be wired for characters. If the two answer back arrangements are required, it will be necessary to prevent the transmission of characters until after eight revolutions of the teletypewriter motor, as the operation is limited by the conditions under which the teletypewriter motor has to be started.

What is claimed is:

1. In a teletypewriter switching system, an automatic teletypewriter transmitter comprising a plurality of pairs of cooperating transmitting contacts, means in said teletypewriter for actuating each of said pairs independently to open or close each of said pairs, a plurality of other pairs of cooperating transmitting contacts, means for opening or closing each of said other pairs independently, one contact of each of said pairs of teletypewriter contacts connected individually with one contact of each of said pairs of other contacts to form a plurality of parallel branches each having two pairs of cooperating transmitting contacts in series, and means for delaying the connection of said parallel branches operatively in circuit in sequence until said transmitter has attained normal operating speed.

2. In a teletypewriter switching system, a teletypewriter station circuit having a plurality of teletypewriter transmitting contacts therein with means for positioning each of said contacts successively in series in said station circuit in the open or closed position, a plurality of other transmitting contacts in said circuit, means for connecting said transmitting contacts and said other contacts successively in series, magnetic means for operating a particular teletypewriter key to establish said series connections and means for maintaining said key continuously in the operated position while an answer back message is transmitted.

3. In a teletypewriter switching system, a station loop circuit, a first pair of contacts in series in said circuit, a plurality of other pairs of contacts, means for disengaging said first contacts operatively from said loop and substituting therefor each of said other pairs in succession, means for positioning said substituted contacts so that they are closed when so substituted, a multibank selector switch in said circuit having a plurality of switch arms and a plurality of terminal banks each cooperating individually with each of said arms, means for positioning each one of said arms in engagement individually with successive terminals on its cooperating bank, means for extending said loop circuit successively through each of a plurality of series circuits comprising one of said switch arms, a terminal on one of said banks and one of said pairs of contacts, means for opening or closing said loopas it is extended through each series circuit, and means for delaying the first of said openings or closings for a definite measured interval.

4, In a teletypewriter switching system, a teletypewriter circuit comprising a multibank selector switch, said switch having a plurality of switch arms connected individually in series with individual teletypewriter transmitting contacts, said switch having also an individual arm and bank for delaying the transmission of teletypewriter signal elements.

5. In a teletypewriter switching circuit, a multibank, rotary selector, a circuit interrupting device for stepping said selector, means for connecting a telegraph circuit in succession to each of a plurality of brush arms on said selector, means for opening or closing said telegraph circuit as said circuit is connected to each brush arm in turn to transmit successive signal elements of a character in accordance with the Baudot code, means for forming successive characters on successive terminal levels of said banks a motor driven teletypewriter transmitter for timing the transmission of signals from said selector and an individual brush and bank on said selector for preventing the transmission of signals until said teletypewriter motor has attained normal operating speed.

6. In a teletypewriter switching circuit, a telegraph station loop circuit, an answer back circuit in said station circuit comprising a selector switch, said selector having a plurality of banks, each bank having a plurality of terminals, means for setting up connections on said selector to transmit successive trains of electrical impulses to form successive characters in accordance with the Baudot code and impulse transmission delay means comprising a closed shunt path across said loop through a plurality of successive terminals on a particular bank on said switch.

'7. In a teletypewriter switching system, a teletypewriter station circuit, an answer back mechanism therein comprising an electric motor coupled to a teletypewriter "transmitter having transmitting contacts for transmitting answer back signals, starting means for said motor responsive to remote control means connected to said circuit and means, comprising a contact bank and cooperating brush arm on a magnetically operated rotary selector connected to said circuit for preventing the transmission of answer back signals until said motor has attained normal operating speed.

8. In combination in a teletypewriter switching system, a teletypewriter station circuit, a teletypewriter transmitter in said circuit, a motor driving said transmitter, a plurality of transmitting contacts on said transmitter, an answer back device comprising a multibank, multiswitch arm, rotary selector connected to said transmitter, a plurality of parallel circuits, each extending individually through one of said switch arms, one of said banks and one of said transmitting contacts, a magnet responsive to a signal received by said circuit for starting said motor to operate said "answer back device, and means connected to said contacts for preventing the transmission of answer back signals until said motor has attained its normal operating speed.

WALTER M. BACON.

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