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VARIABLE COLOR DIGITAL DISPLAY
FOR EMPHASIZING POSITION OF DECIMAL POINT
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a division of my copending application No.
567,323, filed on May 20, 1988, entitled Variable Color ~ .
Digital Multimeter, which is a division of my application No. 527,374, filed on January 15, 1987, entitled Variable ; :-.
Color Digital Multimeter, now Canadian Patent No. 1,261,923 issued on September 26, 1989.
BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to variable color display devices.
2. Description of the Prior Art ~ -The difficulty of rapidly detecting the position of a decimal point in a long string of digits, displayed on a multi-element digital display which includes a large number of display segments, is appreciated in the prior art. :
A monochromatic multi-digit display disclosed in U. S. ~
Patent No. 3,719,849, issued on March 6 7 1973 to Robert L. ~ ;
Steward, dedicates one digit position to a decimal point.
When a string of digits is displayed, only the decimal point is energized on one display digit to provide wide separation i~
between the decimal point and its nearby digits, for improving the readability of the decimal point in a long string of digits. Since one display position is sacrificed, .. ~
the resolution of the display is diminished. ~:
Z01~207 ~ ~ ~
SUMMARY OF THE INVENTION
It is the principal object of this invention to provide an improved variable color digital display.
It is another object of the invention to provide a variable color digital display for exhibiting decimal numbers such that digits that precede the decimal point are illuminated in a first color, and digits that follow the - - -~
decimal point are illuminated in a second color, to more effectively emphasize the position of the decimal point. ~-,: ~,, ,, ' ~ .
BRIEF DESCRIPTION OF THE DRAWINGS
' ~ ~,:.:,: ,' In the drawings in which is shown the preferred embodiment -~
of the invention, FIG. 1 is a schematic diagram of a single 2-primary color `
7-segment display element.
FIG. 2 is an enlarged cross-sectional view of one display segment in FIG. 1, taken along the line 2 - 2. ;
FIG. 3 is a simplified schematic diagram of a variable color digital display for exhibiting decimal numbers such that digits preceding and following the decimal point are `
20 illuminated in respectively different colors. ;~
FIG. 4 is a timing diagram of the circuit shown in FIG. 3.
Throughout the drawings, like characters indicate like ~-;
parts. - i . ,.: . ;:
, . ..., .:,.. ..
2012Z~37 DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now, more particularly, to the drawings, in FIG. 1 is shown a schematic diagram of a 2-primary color common cathodes 7-segment display element 42 which can selectively display various digital fonts in different colors on display segments a, b, c, d, e, f, g, and DP
(decimal point). Each display segment includes a pair of LEDs (light emitting diodes): red LED 2 and green LED 3, which are closely adjacent such that the light signals emitted therefrom are substantially superimposed upon each other to mix the colors. To facilitate the illustration, the LEDs are designated by segment symbols, e. g., the red LED
in the segment a is designated as 2a, etc.
The anodes of all red and green LED pairs are interconnected in each display segment and are electrically connected to respective outputs of a commercially well known common-cathode 7-segment decoder 23. The cathodes of all red LEDs 2a, 2b, 2c, 2d, 2e, 2f, 2g, and 2i are interconnected to a common electric path referred to as a red bus 5. The cathodes of all green LEDs 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3i are interconnected to a like common electric path referred to as a green bus 6.
The red bus 5 is connected to the output of an inverting buffer 63a, capable of sinking sufficient current to forwardly bias all red LEDs 2a to 2i in display element 42.
The green bus 6 is connected to the output of a like buffer 63b. The conditions of red bus 5 and green bus 6 can be controlled by applying suitable logic control signals to the .'~ .- .
~' ;~' .
~0~22(~17 ~-color control inputs R (red), Y (yellow), and G (green), to illuminate display element 42 in a selected color.
The operation of display element 42 will be now explained by the example of illuminating a digit '7' in three different colors. Any digit between O and 9 can be selectively displayed by applying the appropriate BCD code to the inputs AO, Al, A2, and A3 of common-cathode 7-segment decoder 23. The decoder 23 develops at its outputs a, b, c, d, e, f, g, and DP drive signals for energizing selected groups of the segments to visually display the selected number, in a manner well known to those skilled in the art.
To display decimal number '7', a BCD code 0111 is applied to the inputs AO, Al, A2, and A3. The decoder 23 develops high ~ -voltage levels at its outputs a, b, and c, to illuminate ~ ;
equally designated segments a, b, and c, and low voltage ~;
levels at all remaining outputs (not shown), to extinguish ~;
all remaining segments d, e, f, g, and DP. . ~; ;
To illuminate display element 42 in red color, the color `
control input R is raised to a high logic level, and the `
color control inputs Y and G are maintained at a low logic level. As a result, the output of OR gate 60a rises to a high logic level, thereby causing the output of buffer 63a to drop to a low logic level. The current flows from the output a of decoder 23, via red LED 2a and red bus 5, to current sinking output of buffer 63a. Similarly, the current flows from the output b of decoder 23, via red LED 2b and ~ -red bus 5, to the output of buffer 63a. The current flows ~ -from the output c of decoder 23, via red LED 2c and red bus 5, to the output of buffer 63a. As a result, segments a, b, ~;
and c illuminate in red color, thereby causing a visual 4 ~
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: -: ' ~' 20~:207 impression of a character '7'. The green LEDs 3a, 3b, and 3c remain extinguished because the output of buffer 63b is at a high logic level, thereby disabling green bus 6.
To illuminate display element 42 in green color, the color control input G is raised to a high logic level, while the color control inputs R and Y are maintained at a low logic level. As a result, the output of OR gate 60b rises to a high logic level, thereby causing the output of buffer 63b to drop to a low logic level. The current flows from the output a of decoder 23, via green LED 3a and green bus 6, to current sinking output of buffer 63b. Si~ilarly, the current flows from the output b of decoder 23, via green LED 3b and green bus 6, to the output of buffer 63b. The current flows from the output c of decoder 23, via green LED
3c and green bus 6, to the output of buffer 63b. As a result, segments a, b, and c illuminate in green color. The red LEDs 2a, 2b, and 2c remain extinguished because the output of buffer 63a is at a high logic level, thereby disabling red bus 5.
To illuminate display element 42 in yellow color, the color control input Y is raised to a high logic level, while the color inputs R and G are maintained at a low logic level. As a result, the outputs of both OR gates 60a and 60b rise to a high logic level, thereby causing the outputs of both buffers 63a and 63b to drop to a low logic level. The current flows from the output a of decoder 23, via red LED
2a and red bus 5, to current sinking output of buffer 63a, and, via green LED 3a and green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder 23, via red LED 2b and red bus 5, to the XOl;~Z07 output of buffer 63a, and, via green LED 3b and green bus 6, to the output of buffer 63b. The current flows from the output c of decoder 23, via red LED 2c and red bus 5, to the output of buffer 63a, and, via green LED 3c and green bus 6, to the output of buffer 63b. As a result of blending light of red and green colors in each segment, segments a, b, and c illuminate in substantially yellow color.
In FIG. 2, red LED 2e and green LED 3e are placed on the base of a segment body 15 which is filled with a transparent light scattering material 16. When forwardly biased, LEDs 2e and 3e emit light signals of red and green colors, respectively, which are scattered within transparent material 16, thereby blending the red and green light signals into a composite light signal that emerges at the upper surface of segment body 15. The color of the composite light signal may be controlled by varying the portions of the red and green light signals.
The description of a variable color digital display system shown in FIG. 3, which is capable of emphasizing the position of a decimal point in a string of digits, should be considered together with its accompanying timing diagram vlewed in FIG. 4. The display system, which in its exemplary embodiment utilizes eight single-digit variable color displays 46a to 46h, of which only displays 46a, 46b, and 46h are shown, is capable of detecting the position of a decimal point in a string of exhibited digits and of exhibiting in a first color all digits that precede the , ": , .
decimal point and in a second color all digits that follow the decimal point. The decimal point outputs DP of common-cathode 7-segment decoders 23a, 23b to 23h, which may 2(~1~2(37 receive displayable data in a conventional manner (not shown), are scanned in a cyclic sequence by a multiplexer 146 which is incremented by a counter 162d driven by clock l99j of a suitable frequency. When an active high DP output is detected on a certain of decoders 23a, 23b to 23h, the inverting output W of multiplexer 146, which is connected to the Set Direct input SD of DP flip-flop 138j, drops to a low logic level 199n, to force the latter to its set condition.
The Q output of DP flip-flop 138j, which is connected to the D inputs of all flip-flops 138b to 138h, rises to a high logic level for the remaining time of the scanning cycle, to thereby indicate, as may be best observed in FIG. 4 in the line designated F-F 138j Q OUTPUT at waveform l99p, the position of the detected decimal point in reference to the scanning cycle. The decoder 166 is incremented synchronously with multiplexer 146, and, as a result, its outputs Y0 to Y7 are sequentially driven to a low logic level, to trigger in a sequence flip-flops 138b to 138h to states determined by the conditions of their D inputs, respectively, at the time of triggering, as may be best observed in FIG. 4 in the lines designated DEC 166 OUTPUTS Y0 to Y7 at waveforms l99a to l99h. All flip-flops 138b to 138h, which were triggered before the decimal point was located during the scanning cycle, are triggered to their reset state, while all remaining flip-flops 138b to 138h, which were triggered after the decimal point was located, are triggered to their set state. The Y7 output of decoder 166 is connected to the Clear Direct input CD of DP flip-flop 138j, to force the latter to its reset condition at the end of each scanning cycle. The outputs Q and Q of flip-flops 138b to 138h are ..
20~2Z07 ~ ~:
respectively connected to color control inputs R and G of color controls 52b to 52h, to thereby cause all display digits 46b to 46h that precede the instant decimal point to be illuminated in green color, and all remaining display digits 46b to 46h that follow the decimal point to be illuminated in red color. It would be obvious that other - -color combinations may be devised. ~ ~
, " , In brief summary, the invention describes a method of emphasizing the position of a decimal point in a string of ~ ; `
digits by detecting the position of the decimal point in the string of digits, by illuminating in a first color all ,., .: . . .
digits that precede the decimal point, and by illuminating in a second color all digits that follow the decimal point.
A display device was disclosed which includes a string of side by side positioned variable color digital display elements on which a string of digits with a decimal point may be exhibited. The string of digits is scanned by a multiplexer to determine the position of the decimal point.
Color control accordingly illuminates in a first color all display elements that precede the decimal point and in a second color display elements that follow the decimal point.
It would be obvious that persons skilled in the art may resort to modifications in the construction of the preferred :, embodiment described herein, without departing from the spirit and scope of the invention as defined in the appended claims. The principles of the invention are also applicable to numerous diverse types of display devices, such are .-luminescent devices, liquid crystal devices, plasma devices, -;
fluorescent devices, cathode ray tube devices, and the like.
'~'" '-",' :, 201;~207 CORRELATION TABLE :
This is a correlation table of reference characters used in the drawings herein, their descriptions, and examples of commercially available parts.
, # DESCRIPTION EXAMPLE ~ -~
,, , 2 red LED : :
3 green LED
red bus 10 6 green bus 15 segment body 16 light scattering material 23 common cathode 7-segment decoder 74LS49 - ~:
42 variable color 7-segment display element :
46 variable color 7-segment ~isplay digit 52 color control 2-input OR gate 74HC32 63 inverting buffer 74LS240 :
138 D-type flip-flop 74HC74 ~ :~
146 8-input digital multiplexer 74HC151 162 4-bit binary counter 74HC161 , -, ,:
166 1-to-8 lines decoder 74HC138 :~
199 pulse `~
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