Such displays are frequently referred to as electronic travelling image signs and have been provided in dot matrix form incorporating pixels of either incandescent lamps, LED's or liquid crystalls, such as the arrangements disclosed in US Patents 3 384888 (Harnden, Jr. et al), 3 573 790 (Schulenburg Snr. et al), 3 623070 (Johnson et al), 3651 511 (Andrews et al), 4205 312 (Nelson) and 4386 351 (Lowdenslager) . Control of lamps has been effected by ticket tape and relays via optical or mechanical switches, or by using electrical switching through triacs, or the like,.but incandescent lamps are prone to frequent maintenance and are expensive. LED displays have sometimes utilised hardware logic, or a micro-processor, to allow messages to be quickly updated and provide reliable operation with low power consumption, and one such display is described in US Patent 4024531 (Ashby). Where a multi-coloured sign is required individual pixels for each primary colour are used at greatly increased cost, while the resolution has not been good.

One form of travelling image display which does not rely upon illumination of the lights in every column of the dot matrix to achieve apparent fluent movement of characters in a horizontal direction is disclosed in US Patent 4 162 493 (Ross et al). This is achieved by reliance upon the Beta effect and as all of the lights are of a single colour a moving image of one colour is produced against a background of another colour.

DISCLOSURE OF INVENTION It is the object of the invention to provide a multi-coloured illuminated dynamic display which is achieved without substantial increase of the total number of pixels which would otherwise be required for a single colour display.

In accordance with the invention there is provided a display system for creating visual impressions of multi-coloured images travelling in a predetermined plane, said system comprising a dot matrix formation of lines of illuminating elements when energised glowing in at least two colours and arranged so that in progression by

said images of said predetermined plane successive units of said elements differ in colour from their predecessors, storage means for data representative of the images to be displayed by said dot matrix, and a driving circuit for said dot matrix responding to data in said storage means to illuminate said elements corresponding to said data to produce by said dot matrix a discerned image which is perceived to be travelling in one direction in said predetermined plane and includes pixels of a colour which is a blend of at least some of said at least two colours. A feature of the present invention is that the Beta effect is utilised not to reduce the number of columns of the matrix functioning for illumination of the travelling image as proposed by the Ross et al patent, but to obtain blending of light from neighbouring columns of •lights of different colour. It is also a feature of a preferred embodiment that the luminence, or brightness, of individual lights of the dot matrix is controllable to facilitate the creation of many colour hues in the pixels of the resulting image.

Another feature is that such control is obtained simply and reliably by a time division facility.

BRIEF DESCRIPTION OF DRAWINGS The invention will be more clearly understood by reference to the accompanying drawings, in which:

Fig. 1 is a diagram explaining the phenomenon known as the BETA effect;

Fig. 2 shows a preferred pattern of coloured pixels in a dot matrix and used in this invention;

Figs. 3A, B & C show three alternative patterns of pixels for the matrix; Fig. 4 is a block schematic diagram of a preferred form of controlling electrical circuit; and,

Figs. 5 is a block schematic diagram of the colour decode section of the circuit.

BEST MODE OF CARRYING OUT THE INVENTION A multi-coloured illuminated dynamic graphic display of this invention may be presented in an elongated casing provided with a transparent window on a forward face behind which is arranged a dot matrix of LED's (light emitting diodes) 10 arranged in rows and columns

viewable through the window to display when illu intaed a visual impression of images travelling from end to end, top to bottom, or in any direction or directions with respect to the window. In the following description it will be assumed, for purposes of illustration, that apparent movement is from right to lefthand end. A preferred eπrnodiment of electronic control equipment which may be used is now described.

A dot matrix arrangement 25 of LED lights is depicted in Figs. 2 and 3A, 3B and 3C. The LED's, or lights, 10 are composed of two colours (say red and green) arranged in a predetermined pattern, which in Fig. 2 is repetitive alternating columns. Such a pattern is utilised by the present invention where images are perceived to travel from end to end, ie in a horizontal plane, of the display. With a pattern of alternately coloured rows, or diagonals, as shown in Figs. 3A and 3B, functioning will appear to produce a vertical movement. In the case of Fig. 3C the alternation of the columns involves three colours to provide greater variety of colour blend in the display.

The functioning of the present invention takes advantage of the well-known BETA effect phenomenon. This effect is created by the image' retentivity of the human eye which produces an illusion to a viewer of continuous movement when successive lights are viewed in different positions within a certain time period. How this effect is utilised with the present invention is explained with reference to Fig. 1. Should it be assumed that through a shift register 11 latches are successively applied to a consecutive series of columns 12 of lights 10 through the application of clock pulses, and controlled by input data, actual illumination of the lights in columns 12A and 12B will occur. However, due to the retentivity of the human eye, the image at column 12A will continue to be perceived at all of the positions X in columns 12A' and 12A" as well as 12B' and 12B". This effect has in the past been recognised in the design of travelling signs of a single colour as diclosed in said Ross et al US Patent. By providing in column 12A' lights 10 of a different colour from those in column 12A, as depicted in Fig. 2, it has been discovered that a viewer perceives a blending of the two colours in these two columns to produce an image of different colour from both. Furthermore, by disabling say green columns, the moving image is perceived as complete and in say a red colour, while disabling of the red columns results in a perception of a green

coloured image. By means of rapid switching, different columns can be enabled and disabled at different points on the matrix 25 to provide a perception of a multiplicity of.colours. If both red and green columns are successively illuminated the image will be perceived to be coloured

5 yellow. It will be appreciated, of course, that if a third colour

(blue) be incorporated as shown in Fig. 3C, practically every colour in the spectrum can be displayed. Also, it is possible to provide an illuminated background to a travelling image which is of different colour to that of the image by selective illumination of lights 10

10 ^' - other than those utilised in the displayed character. It will be observed that the feature of available multi-colour is thus achieved without the necessity for more closely compacting the lights 10 included within the display. Throughout this specification every picture element as perceived by a viewer will be referred to as a

15 "pixel" regardless of whether it is of primary colour or the result of apparent colour blending. Also reference to "row" is in some instances a reference to either horizontal or vertical rows in the matrix 25. An electronic control circuit for the display is depicted in Figs. 4 and 5. Generally, the method by which apparently travelling

2X) images are created is by Alphanumeric Matrix Scanning. The rows (X) and columns (Y) of the matrix are addressable to allow for ease of driving, decoding and addressing. The dot matrix 25 provides the least number of electrical connection pins required for the number of LED's addressed. An advantage of X-Y addressing is that it can be used with

25. a. read only memory (ROM) 13 which may serve 25 or more matrixes if X-Y addressing is utilised. To generate alphanumeric characters using the matrix a method known as strobing, or scanning, is used. Information is addressed to the display by selecting one row (or one column) of lights 10 at a time and energising via multiplexer 15 the appropriate

30? lights 10 in that row, with the process continuing for the successive rows. Basically such a method is a time-sharing technique between rows (or columns) of the display. After all rows have been selected in a random or predetermined order, the procedure is repeated. Should the scanning frequency be carried out at about 100 times per second, a

35 flicker-free image will result. When the information is strobed from row to row, top to bottom, the display mode is referred to as vertical strobing, whereas should the information be scanned from column to column, left to right, the mode is called horizontal strobing. With

the ability to address each light 10 in the X-Y matrix, images can be made to change their position or shape by electronic control.

It has been found that the perceived brightness of a light 10 can be varied or adjusted by varying the amount of time that it is illuminated within its individual scanned time slot bearing in mind that full illumination of any light 10 might be instantaneous. Using the above matrix scanning each row, or column, is provided available time for a short period on a time sharing basis. In row scanning the available time for each row is typically derived by dividing the total number of rows into 20 ms whereby with 7 rows each will have an available time of about 3ms. The apparent brightness of the lights 10 in the row can be varied by adjusting the period, within the available time, that the light 10 is illuminated. For example, if the first row is only enabled for 30% of its available time, the lights 10 in that row will be perceived as only 307. as bright as lights enabled for 100% of the available time. It is therefore a feature of this invention that by dividing the available time for each row into two parts of 33% and 66% and with the use of column drivers to enable selected lights 10 in the row to effectively generate 4 apparently different brightness levels for each light. If, for example, a light 10 is not enabled during either part of the row's available time it will have a brightness of 0%. If it is enabled for the first part it will have a perceived brightness of 33% and for the second half 66%. If however it is enabled for both parts it will have a brightness of 100%. It will be appreciated that by dividing the available time into more parts that more levels of perceived brightness would be attainable.

By the combination of different coloured lights 10 of differing perceived brightness with the superimposing of the beta effect it is possible to generate almost all of the colours and hues of the spectrum. In the proposed version using red and green primary colours of lights 10 and four levels of brightness, sixteen colours and hues are available. These are: Black

Red - Dull, medium and bright Orange - Medium and bright

Amber - Bright

Yellow - Dull, medium and bright

Lemon - Bright

Lime - Medium and 1 ight Green - Dull, medium and light

Therefore, within the dot matrix 25 any individual light 10 or set of lights can be perceived in any of the available colours. This allows the display of complicated multicolour graphic 'images as well as textual information. An eye-catching feature can be incorporated in the display whenever a perceived coloured symbol occurs on a background of a different colour, by producing a black shadow at the interface at the trailing edge of the image.

A more detailed description of the circuitry of Figs. 4 and 5 will now be provided. Displayed images are obtained by assigning to each of the lights 10 on the display matrix 25 a corresponding bit, or bits, from within the bit mapped memory 13. To change the colour of any pixel in the display image its corresponding bit(s) in the memory 13 merely requires to be so adjusted. A logic level of "1" in the memory 13 corresponds to a foreground coloured pixel while logic level "0" corresponds to a background coloured pixel. With the use of a microprocessor, or computer, adjusting, changing and manipulating the contents of the memory 13 the displayed images may be caused to vary on the dot matrix 25. Digitizers, graphic tablets and VDU terminals, etc, can also be connected to the microprocessor to aid in the generation and control of the digital imagery.

As shown in Fig. 4 the data in the bit mapped memory 13 corresponds only to the foreground and background status of a pixel. The colour and luminence information is stored within the microcomputer and is adjusted as required by the computer on a block basis, eg. for each character. This arrangement is preferred for displays of characters only, in that it allows the assignment of a colour to the foreground pixels and a different colour to the background pixels. The colour combinations can be changed on a character or block basis to allow a choice of any two colours out of the sixteen available, such as a red letter on an amber background. It would be possible for individual pixels to be adjusted for different colour selection, however, this would require much greater computer compacity. It would be possible for each pixel to have a corresponding nibble (4 bits) in the memory 13 so that any pixel can be set to anyone of the sixteen available colour combinations. Although this would require more complicated computing to generate and control images it does allow for easier display of multi-coloured graphics. However, the arrangement

depicted in Fig. 4 is presently preferred.

As shown the memory 13 is a random accessed memory (RAM) and its data contents are capable of being adjusted via the microprocessor data and address buses. Within the memory 13 is stored the digital rendition of the images to be displayed on the dot matrix 25.

Consecutive bytes in the memory 13 correspond to consecutive columns on the matrix and individual bits in each byte correspond to the individual lights 10 in each vertical column in the matrix 25. Therefore, adjacent data bits between bytes correspond to the rows of Tights 10 on the matrix 25, so that data bit DO corresponds to the top horizontal row of the matrix 25 and Dl Dn corresponds to lower rows. As the matrix 25 is multiplexed using vertical strobing new data requires to be loaded periodically into the shift registers 17. Rows of the matrix 25 are refreshed starting with the lowest row Dn and progressing upwardly at approximately 3ms intervals.

As stated above it is a feature of this invention to provide facility for selection of luminence of the lights 10 so as to introduce the facility for selection of colour hues in the coloured graphic display. It would be possible to provide this selection of luminence by relying upon current control applied to the lights 10, but the requirement for independent analogue control of the lights 10, especially necessary with the display of multi-coloured graphic images, would greatly increase the cost of the apparatus. For instance, all of the shift registers 17 would require to provide multipled outputs possibly with different selectable attenuation therein for each of the Tights 10. According to this invention each row is refreshed twice during its 3ms refresh update allowing the display of luminence variations. A timer 23 interrupts the micro-computer at the required interval. When the interrupt signal is received by the micro-computer it suspends all of its operations. Then the luminence sync is reset to "0" logic level corresponding to lights 10 of /., total brightness. The row in the dot matrix 25 to be next updated is selected via a binary digit being set in latch 14 and applied to multiplexer 15 which connects the relevant data bit to the shift register 17 through a colour decoder 16. Then the colour selection for the first character, or graphic block, is set into colour decoder 16 through its latch 21 by the micro-computer.

Using the micro-computer address bus the first byte of the

display data in the memory 13 is placed on the data bus (D0...Dn) and the selected bit is then conveyed through the multiplexer 15 and colour decoder.16 to the shift registers 17. A pulse generated on the system clock causes this bit to be shifted into the first latch 20 of the shift register 17. The address bus is then incremented to place the next byte (column data) on the data bus and it is then clocked into the shift register 17 thereby moving the first bit along by one latch. This process is repeated for all columns with colour changes being made as required between clock pulses. After all bytes have been shifted in, the row select de-multiplexer 18 and the row drivers 19 are adjusted to the selected row via the latch 14, and simultaneously the data in the shift registers 17 is transferred to the latches 20 by a pulse on the PE line. The data in the latch 20 then either enables or disables the drives 22. Each drive 22 is typically a Darlington transistor array which when enabled allows flow of current through itself to ground. The row drivers 19 are typically MOS-fet power transistors of which the selected device allows current to flow through itself from the +HT supply. Hence a circuit is formed through a row driver 19- to a row of the dot matrix 25. Individual LED's 10 in that row are then illuminated if their respective column drives 22 are enabled. Resistors 24 in the columns limit the amount of current that flows through the LED's to about 110mA.

Approximately 1ms after the interrupt from the timer 23 the refresh of that row is repeated with a luminence sync level of "1"

2 corresponding to a brightness of 66 /-% of full luminence. The process is then implemented for each individual row and the total matrix 25 is completely refreshed every 20ms approximately to provide an apparent continuous image to a viewer from the display.

As described above, the dot matrix 25 consists of alternate red and green columns. To display a pure red image only the red columns will be enabled and only the green columns for pure green. To display a yellow or hued image both red and green columns are used and the luminence level of the alternate red or green columns is adjusted to create the required hue. For example, to create a bright lime colour the green lights 10 are enabled for full (100%) luminence, ie they are enabled for both luminence sync levels, the red lights 10 are enabled for 33 IΛ luminence, which when superimposed on each other using the Beta effect create a lime colour. To create different coloured

images on the same screen the colour selection is simply varied before the relevant column data is shifted out.

Colour selection is made by loading an 8 bit binary value into the latch 21 (Fig. 5). The following table shows the possible colour combinations available for foreground and background.

COLOUR SELECTIONS

PINS A -D SELECT FOREGROUND

PINS Al -Dl SELECT BACKGROUND

D C B A COLOUR

0 0 0 0 BLACK

0 0 1 0 RED

0 0 1 1 BRIGHT RED

0 1 0 0 DULL GREEN

0 1 0 1 DULL YELLOW

0 1 1 0 ORANGE

0 1 1 1 BRIGHT ORANGE

0 0 0 GREEN

0 0 1 LIME

0 1 0 YELLOW

0 1 1 AMBER

1 0 0 BRIGHT GREEN

1 0 1 BRIGHT LIME

1 1 0 LEMON

1 1 1 BRIGHT LEMON

For example, if the Hex value 8E is selected the colour of the foreground data is green and the background is lemon. Serial data enters the multiplexer 22 through PIN 9. A "1" level signifies a foreground selection and a "0" level signifies background. Integrated circuit toggle 23 divides the system clock by 2 providing colour synchonisation between the multiplexer 15 and the columns on the matrix 25 where a level of "1" on PIN 6 of toggle 23 corresponds to a red column on the matrix 25 and a level of "0" corresponds to a green column, or vice versa, depending on the actual matrix arrangement used. Integrated circuit 24, being a shift register, and its associated gates 25 and 26 produce trailing shadows on characters. If the incoming serial data bit is "0" (ie background information) and the prior data bit (available on PIN 3) is "1" (ie foreground) the current bit will be totally disabled by taking PIN 7 of multiplexer 17 to level

"1", creating a black trailing edge behind the character. It will be appreciated that with the use of a larger multiplexer 22 the trailing shadow could be decoded to any of the available colours. If, for example, the incoming serial data is "1" signifying a foreground

5. selection, the colour selection is a red foreground on a black background by setting the numeral 20 Hex into latch 21. When the luminence sync is "0", signifying 33% luminence, or the colour sync is "0" signifying a green column, the output of the multiplexer 23 will be "0" and the associated light 10 will not be illuminated. However,

10? when the luminence sync is "1" and the colour sync is "1" an output leveT of "1" will be output from multiplexer 23 and the light 10 illuminated. Therefore, multiplexer 22 forms a digital grid or filter sα that only the relevant column of lights 10 are illuminated at the relevant times (and therefore luminence levels) to produce the

15 ^* selected colour and hues.

Protection timer 27 is a re-triggerable monostable integrated circuit which is strobed by the system clock. A single clock pulse will hold the output high for approximately 3.5ms. If, however, the system clock fails for any reason the output will go low resetting the

20 shift registers 17 and disabling the row drivers 19. This prevents any possible damage to the LED's 10 caused by continuous high ^* current flowing through them.

A preferred embodiment has now been described but it should be understood that other forms and modifications, of which some are

25- referred to herein, are possible within the scope of this invention. For instance, while the preferred embodiment uses Light Emitting Diodes (LED) as individual lights 10, it is noted that any Luminous device or substance or light controlling device or substance could be utilised to obtain the beta colour mixing effect. Among these are

30 Liquid Crystal Displays, Electro-mechanical display, Vacuum Fluoresent displays, Neon Displays, and incandesecant displays. It is also possible to use a multiplicity of different types of lights in a hybrid combination. For example, red and green LED's may be used with blue NEON lights to obtain all the primary colours.

35 It is desired to explain that it has been found in multiplexing the present display that during the time taken to change the column data information, the display is inactive. This means that the more columns in a display the shorter the available time assigned to each

row. This has the effect of severely limiting the number of columns that can be addressed and an overall reduction of the brightness of the display. To offset this problem, it will be noted that the preferred embodiment includes a latch integrated circuit 20 between the shift registers 17 and the column drivers 22. This allows the display to remain active while column data is being changed by virtue that the latches retain the previous information until a pulse on the PE pin of the latch transfers the new data to them from the shift registers 17.