US3728714A

US3728714A - Non-flickering display system having multi-phase power source

Info

Publication number: US3728714A
Application number: US00123341A
Authority: US
Inventors: P Kolesar; R Payne
Original assignee: Stewart Warner Corp
Current assignee: Stewart Warner Corp
Priority date: 1971-03-11
Filing date: 1971-03-11
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17

Abstract

A display system for showing display frames in rapid sequence to form an animated portrayal or the like. A multi-phase alternating-current power source is employed to energize a display board which has a matrix of electric lamps arranged in separate groups each associated with one of said alternatingcurrent power phases. A triac is associated with each lamp to connect the lamp to said power source. The triacs are appropriately gated to energize the individual lamps of the matrix as required by the input information.

Description

United States Patent Kolesar et al.

[451 Apr. 17, 1973 NON-FLICKERING DISPLAY SYSTEM HAVING MULTI-PHASE POWER SOURCE Inventors: Paul M. Kolesar, Hanover Park; Robert A. Payne, Des Plaines, both of ill.

Stewart-Warner Chicago, Ill.

Filed: Mar. 11, 1971 Appl. No.: 123,341

Assignee: Corporation,

US. Cl ..340/334 Int. Cl ..G09f 9/34 Field of Search ..340/324 R, 334, 336,

References Cited UNITED STATES PATENTS Andersen ..340/ 3 39 3,550,l l2 12/1970 Schulenberg, Sr. et aI ..340/334 3,493,957 2/ 1970 Brooks ..340/ 334 3,432,846 3/1969 Jones et al.

3,594,762 7/1971 Gardberg et al ..340/334 Primary Examiner-John W. Caldwell Assistant Examiner-Marshall M. Curtis Attorney-Augustus G. Douvas, Willaim J. Newman and Norton Lesser [5 7] ABSTRACT A display system for showing display frames in rapid sequence to form an animated portrayal or the like. A multi-phase alternating-current power source is employed to energize a display board which has a matrix of electric lamps arranged in separate groups each associated with one of said alternating-current power phases. A triac is associated with each lamp to connect the lamp to said power source. The triacs are appropriately gated to energize the individual lamps of the matrix as required by the input information.

4 Claims, 3 Drawing Figures LINEI,ROWI

BD CIRCUIT LINE-I.CONT

BOARD CIRCUIT "LINE I,ROWS 2-IO LINE-2 BOARD CIRCUIT LINE 2,ROWS I- I0 LINE-3 BOARD CIRCUIT LINE 3,ROWS l-IO SHEET 1 BF 3 COL. IOO

CCCCCCCCCCCC CCOCOCCCC 4 PATENTED APR 1 71375 Q 1 4 E MM Mm Mm W M L L L L L( j \k( J L 2 T w W WW WW WW W m mm mm. mm m 00000006OCCCCCCCCOOOOOOOCOOCOOOO0CCCCOO 0C 0 OCC CO OCCC O 0 CCC C O C C 0' CC C C O C C P O CO C C C C C C O O C 0 C CC C C C C O C O C C CC 0 C000 0 O C O CCCCCC A Q Y INV ENTOR 5 Paul M. Kolesor Robert A. Payne By Attornev PATENTEUAPR 1 H915 3,728,714

SHEET 3 UF 3 M B c 3Q I i 6OHZ.

A a c A B c A B c V430 Fb (43 PM Par PM 430 PM Kw) q T i A Trig B Trig /C Trig rA Trig B Trig C Trig Trigger '380 38b "38c 380' W385 IF38C' n n (c) y #7500) 38a 48b [t me ad .485 '486 H (d) A mqsr Dom U Flow I (e Line I Line2 Line?) Line4 Linel3 Line|4 INVENTORS Paul M. Kolesur Robert A.Poyne AHornev NON-FLICKERING DISPLAY SYSTEM HAVING MULTI-PHASE POWER SOURCE BACKGROUND OF THE INVENTION It is known that animated characterizations or cartoons may be presented on an electric lamp display board utilizing a system which is operable only by means of digital coding and digital handling techniques without the use of optical devices such as movie projectors, photocells, etc. A system utilizing such a technique is shown in US. Pat. No. 3,638,215, issued Jan. I972 to Robert A. Payne. However, it has been discovered that in the operation of such a display system certain visual phenomena can occur which are quite disturbing to the viewer of the display. This visual phenomena presents itself as a sort of flickering during the presentation of amination displays which is caused by the manner in which the data is handled to present the rapidly sequencing frames. In these systems address and display data is read from an input device and through the logic control to the display board circuits to enable the lamps for forming each frame. The data read-in thus required a finite amount of time and in the previous systems that was done between each display frame. That is, between each animation frame the address and display data for the next frame was entered and manipulated during which period the display board lamps were blanked or turned off. The blanking periods between the frames were quite short since the digital data for the whole board could be manipulated on the order of milliseconds, but in spite of the short duration the periodic occurrence of such caused a noticeable flickering, much in the manner of that seen in oldtime movie films.

The flickering is caused by the fact that the frame blanking occurs at a lower rate than the flicker fusion frequency of the human eye, the flicker fusion frequency being the minimum rate at which a light may be turned on and off and still appear to the human eye as a steady light. The system disclosed in the aforementioned application had a frame change rate of two. to four frames a minute so that all of the lamps on the board were simultaneously turned off or blanked at that rate. The minimum flicker fusion frequency, under the most ideal conditions, is between forty and 45 flashes per second, however, so that the flicker was quite noticeable.

SUMMARY OF THE INVENTION Applicants provide by this invention a system which is not subject to this flickering phenomena even when operating in a rapid frame changing mode to present animation displays. In a system embodying the techniques of this invention the energization of the lamps and the routing of the address and display data through the control system are synchronized in such a manner so that the flow of data has no effect on the energizing electric power flowing to the lamp bulb.

The inventive system contemplates the use of a fluctuating power source for energizing the lamp along with a memory type of lamp switch such as a thyratron or thyristor type of device so that the data may be manipulated through the control system in between the lamp energization time of each power fluctuation. The data handling can then be synchronized to manipulate the data during the period the lamps are lit and will not disturb the actuation of the lamps. More particularly, the flickering problem is eliminated in a system which comprises a display board including a plurality of display lamps, a fluctuating power source such as an alternating current source for energizing the display lamps and means for initiating the actuation of the display lamps at a desired point of each fluctuation of the power source, the initiating means taking the form of a thyratron or thyristor type of device. The initiating means also includes means for actuating the thyratron or thyristor at the desired point of the fluctuating .power signal. In addition, means are provided for programming the operation of the lamps by the manipulation of electric data signals to cause the display lamps to form the display frames in rapid sequence, along with means for synchronizing the programming means and the thyratron or thyristor initiating means so that the programming means manipulates the data signals only during the periods between the desired initiating points of the fluctuating power signal.

In a system of this type the display board lamps are energized, for example, by the ordinary commercial frequency of 60 hertz (or energization frequency of I20 hertz) but the digital data is manipulated through the system during periods of each cycle that will have no effect on the energization of the lamps. Thus, even though data is manipulated at a frame rate below the flicker fusion frequency of the eye, there is no noticeable flickering to the observer of the display because the data is synchronized with the frequency of the power source.

This invention along with its advantages and features will become more understandable with a further reading of the description of a preferred embodiment following hereinafter, especially when taken in view of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial view of a solid matrix of displayed lamps making up a display board to which the teachings of this invention may be applied;

FIG. 2 is a block diagram of the control circuits for a display system embodying the teachings of this invention; and

FIGS. 3a through 3e are voltage waveform timing diagrams of the electric signals at various parts of the system of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention is particularly adaptable to a display system in which messages and animated displays are produced on a display board 10 of the type shown in FIG. 1 comprising a matrix of lamps 12 such as incandescent bulbs. The board is similar to the type shown and described in the previously mentioned Payne patent in that it is made up of a plurality of separate horizontally disposed lamp matrices designated in FIG. I as Line 1, Line 2, etc. Each line matrix is formed by a plurality of lamp rows and a plurality of lamp columns. As in the aforementioned patent, each lamp row is associated with board circuit 14 (FIG. 2) containing a shift register 16 having a stage therein sequentially corresponding to each lamp in the row. It will be noted that matrices forming the lines in the system of this application are slightly larger than in said patent in that each comprises ten horizontal rows and 120 vertical columns. This disclosure is in fact based on the display system installed in the Three Rivers Stadium in Pittsburgh, Pennsylvania by the assignors of this invention and that board is made up of fourteen such lines arranged in two groups of seven lines high, arranged sideby-side to form one large solid display lamp matrix.

Each of the lines formed by its group of rows is individually addressable so that a word message may be formed by the input of alpha/numeric data into the shift registers or pictorial representations may be formed by the input of column-by-column lamp code data in the manner described more fully in the aforementioned Payne application. Briefly, however, the word messages are read in from an input device such as a punched tape typewriter/reader, a magnetic memory, or even a general purpose computer in a bit by bit manner, each of which is representative of an alpha/numeric character and the characters are read in to the addressed line a column at a time from the right-hand side of the board and are shifted to their desired column location. The pictorial representations are very similar except that the data from the input device does not represent a character. Rather, the data represents the status of each of the ten lamps forming a column in the line. Thus, each data bit coming from the input means must contain at least 10 bits to represent the ten lamps in the column plus another bit for indicating the bit is representative of an alpha/numeric character or a lamp code representation. 7

To form an animated display in the system described in the aforementioned Payne application, the data for each frame is read into and through the system to the board during the blanking period between the rapidly changing frames. That is, between each frame of the dinate the data in the shift register stages with synchronizing data, in a manner to' be described, so as to fire the switches 20-1 through 20-120 at a proper time to cause the desired lamps to actuate in accordance with the animated pattern. In the present example the switches are shown as triacs in view of the alternating current power utilized for energizing the board lamps 12; however, the use of other devices is contemplated also. The board circuits will be discussed in more detail later with respect to the waveforms and timing diagram shown in FIGS. 3a through Be.

The board circuits 14 are controlled, as in the previously mentioned patent, by means of a signal logic circuit 22 which operates responsive to data received from data input means 24 which may take the form of any data generating or storage device such as a tape reader, a memory storage or even a general computer. When data is received from the data input 24 by the logic control circuits 26, it is channelled to various function circuits including a line address circuit 28, column address circuit 29, a lamp encoder circuit 30, or a line blanking circuit 32, as may be appropriate.

The line address information contained in the input animation, which changed at a rate of perhaps two to four frames per second, all of the lamps on the board were turned off for a period of time to permit the data to be read in and through the control system. This caused a flicker which was noticeably disturbing to an observer and it is to the elimination of this flicker to which this invention is directed.

FIG. 2 shows a system utilizing the techniques of this invention and is a simplified block diagram incorporating most of the features of the control system described in the aforementioned application. Since there are other control systems that could be used to manipulate the data between the input means and the display lamps without departing from the inventive concept, the particular one used in the present embodiment is only described in broad terms with appropriate references back to the aforementioned Payne patent. The system comprises the display board 10 with its lamps 12 which are controlled by the board circuits 14, each ofwhich is associated with one of the rows 1 through 10 forming the

Lines

1, 2, 3, etc. As previously indicated, the board circuit 14 for each row comprises a shift register 16 having a stage 16-] through 16-120 sequentially associated with a respective lamp 12-1 through 12-120 in that row. The data contents of each shift register stage after the data read-in controls the actuation of its respective lamp by means of a gate 18-1 through 18-120 and a thyratron or thyristor type switch 20-1 through 20- 120. The gates 18-1 through 18-120 coordata causes the line address circuit 28 to complete a circuit for applying line shift pulses to the trigger inputs of all of the flip-flops forming the shift registers of the particular line addressed. The display character information which is included in the input data is handled by the lamp encoder circuit 30 in a manner appropriate to the type of data being inputted, and the lamp row encoding signals are provided to the data inputs of each of the board circuit shift registers forming all of the lines 1 through 14. Although the encoding signals appear at the input to all shift registers, they will only be shifted into the shift register of the addressed line because that is the only one which receives the shift pulses from the line address circuit 28. The lamp row encoding signals are shifted through the shift registers of the addressed line to the appropriate stages in accordance with the input data as controlled by a column position control. This can be done in a cycling mode to a specific column addressed in the input data application, or in a noncycling mode to a column position determined by the number of input data characters as explained in detail in the Payne patent. The fourteen lines making up the display board are separately controlled to receive the display data in any order dictated by the address data contained in the input.

The line blanking circuit 32 is provided to permit the complete read-in of an alpha-numeric message before energizing the lamps. This gives the appearance that the board lamps are all being lit simultaneously in spite of the fact that the data for each line was read intoand through the logic in a serial manner. Although the blanking circuit 32 was used in the display of animation characterizations in the system as described in the previous patent to enable the manipulation of data between frames, it is not ordinarily used in the display of animations in accordance with the present invention.

The remaining circuits in the signal logic 22 which have not yet been mentioned operate in conjunction with the described signal logic circuits and the board circuits in a unique manner to eliminate the need for blanking the display board between each frame of an animated cartoon. They operate to synchronize the read-in of the address and display data for forming the frames with the other control functions so that the display need not be visually disturbed.

The lamps of this system are energized by a pulsating power signal which in the particular example described is provided by a 3-phase 60 hertz power source appearing at terminals 34a, 34b, 34c. The 3-phase source is used because of the large number of lamps forming the display board and hence the great amount of power consumed. The 3-phase power, of course, enables a substantial savings in the amount of copper needed for energizing a large power consuming load such as a display lamp matrix board. It will be recognized, however, as this description proceeds that the teachings of this invention are also applicable to single phase systems and even to a pulsating dc. power systems such as fullwave or halfwave rectified unfiltered types.

Referring again to FIG. 2, it will be seen that the lamps 12 of different lines are connected to separate power phase conductors, this being done to equalize the loads on the three phases. Thus, the lamps of line 1 are connected to the A phase terminal 340 while the lamps of line 2 are shown connected with the B phase terminal 34b and the line 3 lamps are connected to the C phase terminal 340. The 3-phase power signals are shown in FIG. 3a. The shaded portions 36 at the beginning of each half cycle of each waveform indicates that provisions are made for controlling the brightness of the lamps by controlling the phase angle of the point in each cycle at which the lamps are turned on with respect to the period of the total half cycle. This is accomplished in a well known manner by controlling the triggering point of the triacs 243-1 through -120 series connected with each lamp 12 between ground and its respective power signal phase source conductor. If a triac trigger pulse is received at the gate of each triac at the time indicated at 38a, 38b, 380 in FIG. 30, with respect to the associated three phase signal 37a, 37b, 37c appearing at its anode, as shown in FIG. 30, then the associated lamp will be energized for less than a full half cycle. A variation in this phase relationship will be'noticeable to an observer as a change in the illumination level of the lamp since the human eye actually integrates the light pulses. The message board located in the Pittsburgh Three Rivers Stadium has the capability of adjusting the timing of the triac trigger pulses 38 with respect to the 3-phase a.c. signals 37a, 37b, 37c to adjust the level of lamp brightness because it is to be used for nighttime and daytime activities and the light level required in the daytime will make the display bloom uncomfortably in the darkness of night time. The brightness control is accomplished by a zero crossing synchronous pulse generating circuit 40 of any well known type and a bright/dim circuit or phase shifter 42. The zero crossing synchronous pulse generating circuit 40 produces

pulses

43a, 43b, 43c on the respective phase outputs at the zero crossing points of the respective phase power signals 37a, 37b, 370 in a well known manner. The bright/dim circuit 42 in its simplest form comprises a signal delay circuit for each phase. The delay circuit for each phase has a two level time delay selector which is actuatable by means of input data detected by the logic control 26 to select the desired lamp level. The bright/dim control supplies the appropriately delayed

triac trigger pulses

38a, 38b, 38c

on the

corresponding output conductors

44a, 44b, 44c to an input of each of the corresponding phase board circuit gates 18-1 through 18-120. The

triac trigger pulses

38a, 38b, 38c pass through any gate 18-1 through 18-120 which has been opened by the presence of data in the corresponding stage of the associated shift register 16 and tires the triac to cause the associated lamp 12 to be lit. Those triac devices 20-1 through 20-120 which have been fired will maintain their respective lamps 12 lit for the remaining portion of the half power cycle regardless of what occurs on their control gate electrodes from the gates 181 through 18-120 and the point during the half cycle at which they are fired determines the apparent brightness of the lamps.

Since the triacs will remain conducting for the remainder of each half cycle for which it is triggered, the address and display data may be manipulated during the periods between the trigger pulses. Thus, in accordance with the teachings of this invention the data manipulation circuits are synchronized with the trigger pulses so as to shift data onlyduring the periods between the,

successive trigger pulses

38a, 38b, 380, 38a, 38b, etc.

The flow of data is synchronized with the triac trigger pulses by means of a signal from the bright/dim circuit 42 on conductor 46 having a waveform as shown in the timing diagram of FIG. 3d. As may be seen, this signal has

pulses

48a, 48b, 480 which are representative of the respective

triac trigger signals

38a, 38b, 38c, but delayed therefrom by a short time of, for example, 500 microseconds. Each of these pulses actuates the data flow control circuit 50 which then causes the logic control 26 to signal the data input means 24 to transmit a block of data signals. This block, of course, must be small enough to be read in before the occurrence of the trigger pulse. If the display board is small enough and the data handling circuits are fast enough, a block may contain all of the data for the formation of a complete display frame of the animation and'therefore may be read in between

adjacent trigger pulses

38a, 38b, 380. However, in the particular example described, in which the board comprises 14 separately addressable lines, it is impossible to transmit the data for all fourteen lines constituting a complete frame during the 2.78 milliseconds period occurring between adjacent triac trigger pulses. There is suitable time, however, for transmitting the data for a single line since, as shown in FlG 3e, that takes less than 1.30 milliseconds. In this manner the data for a complete frame of 14 lines can be transmitted between the occurrences of 15 successive triac trigger pulses or within a time period of approximately 39 milliseconds. This is fast enough to permit a very rapid frame rate and, in fact, the system described is designed to display animated cartoons at a frame rate of up to l5 frames per second. In spite of the fact that that is substantially slower than the flicker frequency, the observer of the display is not able to detect any flickering because the lamp energizing power is not being affected by the read-in and manipulation of the address and display data.

It can be seen that a further benefit accrues from the synchronization of the data flow with the periods between the lamp energizing pulses. In the particular system described it is possible that up to 5600 light bulbs will be energized with each trigger pulse. That number of bulbs being energized at the same time can cause some very large and disruptive transients in the power circuits. Such transients can be particularly destructive to data flowing through logic circuits at the same time unless special precautions are taken. In the system of the invention, of course, there is no data flowing during the critical part of the cycle when the lamps are first turned on so that disturbances to the data flow from that cause is virtually eliminated.

While a preferred embodiment has been described as exemplifying the present invention, it is to be understood that modifications might be made thereto without materially deviating from the invention. For example, the system can be made operable from a single phase a.c. source instead of a 3-phase source in a very obvious manner. Furthermore, the system could be quite simply modified to operate with a pulsating d.c. source such as from a halfwave or fullwave rectified power supply if the triacs -1 through 20420 are replaced by thyratrons or thyristor type devices like silicon controlled rectifiers.

What is claimed is:

1. in a display system for showing display frames in rapid sequence to form an animated portrayal, or the like, the combination comprising a display board including a plurality of display lamps, a fluctuating power source for energizing said display lamps, means for initiating the actuation of said display lamps at a desired point of each fluctuation of said power source, means for programming the operation of said initiating means by the manipulation of electric data signals to cause said display lamps to form said display frames in rapid sequence, means for synchronizing said initiating means and said programming means to cause said programming means to manipulate said data signals only during the periods between said desired points of said fluctuating power signal, wherein said fluctuating power source comprises a thyristor associated with each lamp for connecting same with said a.c. power source and means for actuating said thyristor at the desired points of said a.c. power signal, wherein said synchronizing means comprises means for actuating said programming means to manipulate said data a predetermined time interval after the actuation of said thyristors, wherein said a.c. power source is a three phase source, wherein each of said three phases of power are distributed to separate groups of lamps and their associated thyristors, wherein said thyristor actuating means separately actuates each group of thyristors, and wherein said programming actuating means actuates said programming means to manipulate said data a predetermined time interval after the actuating of each group of thyristors.

2. In a display system for showing display frames in rapid sequence to form an animated portrayal, or the like, the combination comprising a display board including a plurality of display lamps, a fluctuating power source for energizing said display lamps, a fluctuating power source for energizing said display lamps, means for initiating the actuation of said display lamps at a desired point of each fluctuation of said power source, means for programming the operation of said initiating means by the manipulation of electric data signals to cause said display lamps to form said display frames in rapid sequence, means for synchronizing said initiating means and said programming means to cause said programming means to manipulate said data signals only during the periods between said desired points of said fluctuating power signal, wherein said fluctuating power source comprises an a.c. power source, wherein said initiating means comprises a thyristor associated with each lamp for connecting same with said a.c. power source and means for actuating said thyristor at the desired points of said a.c. power signal, wherein said synchronizing means comprises means for actuating said programming means to manipulate said data a predetermined time interval after the actuation of said thyristors, wherein said thyristor actuating means comprises means for providing a triggering pulse during each cycle of the a.c. power signal to the control electrode of each thyristor, means for varying the phase angle of said triggering pulse with respect to said a.c. signal to control the brightness of said display, wherein said a.c. power source is a three phase source, wherein. each of said three phases of power are distributed to separate groups of lamps and their associated thyristors, wherein said thyristor actuating means separately actuates each group of thyristors, and wherein said programming actuating means actuates said programming means to manipulate said data a predetermined time interval after the actuating 3. In a display system for showing'display frames in rapid sequence to form an animated portrayal or the like, the combination comprising a multi-phase ale. power source, a display board including a matrix of electric lamps arranged in separate groups each associated with one of said a.c. power phases, a triac associated with each lamp for connecting same to said power source, means for providing a triggering pulse during each half cycle of itsassociated phase of the a.c. power signal, at least one shift register associated with each group of lamps, each stage of shift registers being associated with a separate lamp, means for providing data signals to the inputs of said shift registers and shifting said data signals through said stages pertaining to the desired condition of each respective lamp to form said display frames in rapid sequence, a gate associated with each lamp having its output coupled to the control electrode of its associated triac to actuate same upon the opening of said gate, means for coupling said triggering pulse means and the output of each stage of said shift registers to the input of the associated gates, and means operative responsive to each of said triggering pulses for controlling the timing of said data signal providing and shifting means so as to operate only during the periods between said triggering pulses.

4. In the display systems of claim 3 wherein means are provided for varying the phase angles of said triggering pulses with respect to said three phase a.c. power signals to control the brightness of the display, and wherein said timing control means comprises means for enabling the operation of said data signal providing and shifting means a predetermined time interval after each triggering pulse.

k I l

Claims

2. In a display system for showing display frames in rapid sequence to form an animated portrayal, or the like, the combination comprising a display board including a plurality of display lamps, a fluctuating power source for energizing said display lamps, means for initiating the actuation of said display lamps at a desired point of each fluctuation of said power source, means for programming the operation of said initiating means by the manipulation of electric data signals to cause said display lamps to form said display frames in rapid sequence, means for synchronizing said initiating means and said programming means to cause said programming means to manipulate said data signals only during the periods between said desired points of said fluctuating power signal, wherein said fluctuating power source comprises an a.c. power source, wherein said initiating means comprises a thyristor associated with each lamp for connecting same with said a.c. power source and means for actuating said thyristor at the desired points of said a.c. power signal, wherein said synchronizing means comprises means for actuating said programming means to manipulate said data a predetermined time interval after the actuation of said thyristors, wherein said thyristor actuating means comprises means for providing a triggering pulse during each cycle of the a.c. power signal to the control electrode of each thyristor, means for varying the phase angle of said triggering pulse with respect to said a.c. signal to control the brightness of said display, wherein said a.c. power source is a three phase source, wherein each of said three phases of power are distributed to separate groups of lamps and their associated thyristors, wherein said thyristor actuating means separately actuates each group of thyristors, and wherein said programming actuating means actuates said programming means to manipulate said data a predetermined time interval after the actuating of each group of thyristors.

3. In a display system for showing display frames in rapid sequence to form an animated portrayal or the like, the combination comprising a multi-phase a.c. power source, a display board including a matrix of electric lamps arranged in separate groups each associated with one of said a.c. power phases, a triac associated with each lamp for connecting same to said power source, means for providing a triggering pulse during each half cycle of its associated phase of the a.c. power signal, at least one shift register associated with each group of lamps, each stage of shift registers being associated with a separate lamp, means for providing data signals to the inputs of said shift registers and shifting said data signals through said stages pertaining to the desired condition of each respective lamp to form said display frames in rapid sequence, a gate associated with each lamp having its output coupled to the control electrode of its associated triac to actuate same upon the opening of said gate, means for coupling said triggering pulse means and the output of each stage of said shift registers to the input of the associated gates, and means operative responsive to each of said triggering pulses for controlling the timing of said data signal proViding and shifting means so as to operate only during the periods between said triggering pulses.