Dual variable color measuring system

[0002] This is a division of my application Ser. No. 08/910,080, filed on Aug. 12, 1997, entitled Variable Color Display System, now U.S. Pat. No. 6,018,237 which is a division of my application Ser. No. 08/571,246, filed on Dec. 12, 1995, entitled Variable Color Display System, now U.S. Pat. No. 5,656,935 issued on Aug. 12, 1997, which is a division of my application Ser. No. 08/187,350, filed on Jan. 27, 1994, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 5,475,300 issued on Dec. 12, 1995, which is a division of my application Ser. No. 07/865,460, filed on Apr. 9, 1992, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 5,283,517 issued on Feb. 1, 1994, which is a division of my application Ser. No. 07/628,328, filed on Dec. 14, 1990, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 5,122,733 issued on Jun. 16, 1992, which is a division of my application Ser. No. 07/197,322, filed on May 23, 1988, entitled Variable Color Digital Multimeter, now abandoned, which is a division of my application Ser. No. 06/819,111, filed on Jan. 15, 1986, entitled Variable Color Digital Multimeter, now U.S. Pat. No. 4,794,383 issued on Dec. 27, 1988.

[0003] Reference is also made to my related applications Ser. No. 06/817,114, filed on Jan. 8, 1986, entitled Variable Color Digital Timepiece, now U.S. Pat. No. 4,647,217 issued on Mar. 3, 1987, Ser. No. 06/919,425, filed on Oct. 16, 1986, entitled Electronic Timepiece with transducers, now U.S. Pat. No. 4,687,340 issued on Aug. 18, 1987, Ser. No. 06/926,511, filed on Nov. 3, 1986, entitled Electronic Timepiece with Physical Transducer, now U.S. Pat. No. 4,705,406 issued on Nov. 10, 1987, Ser. No. 07/150,913, filed on Feb. 1, 1988, entitled Variable Color Display Typewriter, now U.S. Pat. No. 4,824,269 issued on Apr. 25, 1989, Ser. No. 07/336,080, filed on Apr. 11, 1989, entitled Variable Color Display Typewriter, now U.S. Pat. No. 4,934,852 issued on Jun. 19, 1990, Ser. No. 06/839,526, filed on Mar. 14, 1986, entitled Variable Color Display Telephone, now U.S. Pat. No. 4,726,059 issued on Feb. 16, 1988, Ser. No. 06/940/100, filed on Dec. 10, 1986, entitled Digital Voltmeter with Variable Color Background, now U.S. Pat. No. 4,831,326 issued on May 16, 1989, Ser. No. 06/922,847, filed on Oct. 24, 1986, entitled Continuously Variable Color Display Device, now U.S. Pat. No. 4,845,481 issued on Jul. 4, 1989, Ser. No. 07/322,341, filed on Mar. 13, 1989, entitled Continuously Variable Color Optical Device, now U.S. Pat. No. 4,965,561 issued on Oct. 23, 1990, Ser. No. 07/379,616, filed on Jul. 14, 1989, entitled Variable Color Digital Display for Emphasizing Position of Decimal Point, now U.S. Pat. No. 5,003,298 issued on Mar. 26, 1991, Ser. No. 06/920,740, filed on Oct. 20, 1986, entitled Step Variable Color Display Device, now abandoned, Ser. No. 06/931,626, filed on Nov. 17, 1986, entitled Variable Color Hybrid Display Device, now abandoned, Ser. No. 07/157,603, filed on Feb. 19, 1988, entitled Variable Color Multiplexed Display System, now abandoned, and Ser. No. 07/000,478, filed on Jan. 5, 1987, entitled Variable Color Digital Tachometer, now abandoned, which describe the devices employing a variable color display.

[0004] 1. Field of the Invention

[0005] This invention relates to measuring instruments utilizing a variable color digital display.

[0006] 2. Description of the Prior Art

[0007] A display device described in U.S. Pat. No. 3,740,570, issued on Jun. 19, 1973 to George R. Kaelin et al., uses special LEDs that exhibit different colors when subjected to different currents. The LEDs are biased by pulses of different amplitudes, to achieve different colors of the display, and by the length inversely proportional to the pulse amplitude, to compensate for variable brightness of the display caused by different amplitudes of the pulses.

[0008] A circuit employing a dual-color LED driven by a dual timer is described in the article by Bill Wagner entitled 2-color LED+driver=versatile visual effects, published on Oct. 2, 1980 in EDN volume 25, No. 19, page 164. Since dual-color LEDs are connected to conduct currents in opposite directions, it would be impossible to forwardly bias them simultaneously.

[0009] An electronic display having segments wherein each segment is capable of selectively illuminating two colors is disclosed in U.S. Pat. No. 4,488,149 issued on Dec. 11, 1984 to William A. Givens, Jr. Two AND gates are provided for biasing, in each display segment, either a first light emitting diode, for emitting a first color, or a second light emitting diode, for emitting a second color. It is not contemplated to illuminate both light emitting diodes in each segment simultaneously for blending the colors.

[0010] A multi-colour LED display for seven segment figures is disclosed in German Patent No. 3,009,416 issued on Sep. 17, 1981 to Klaus Gillessen. The LED circuit consists of seven group of diodes, each group made up of two diodes, one red and one green. The cathodes of all red diodes are terminated in a common connection, and the green ones likewise, the anodes of each pair of diodes being common for that pair. Two transistors connected in cascade are utilized for activating either all green LEDs, or all red LEDs, but not both simultaneously. When a low level signal is applied to the base of the first transistor, the first transistor is blocked, and the second transistor is turned ON to illuminate the second set of the diodes. When a high level signal is applied to the input of the first transistor, the first transistor is turned ON, while the second transistor is blocked, whereby the first set of the diodes is illuminated. Since the first transistor cannot be simultaneously turned ON and OFF, it would be impossible to illuminate the two sets of the diodes simultaneously. In another embodiment is shown a multi-colour LED display utilizing three sets of LEDs: red, green, and blue, which are respectively commonly connected and may be activated by manual switches. It is not contemplated that the three sets of LEDs be activated in selective combinations to blend the colors.

[0011] A digital electrooptical display with anti-parallel light emitting diodes is disclosed in East German Patent No. 220,844 issued on Apr. 10, 1985 to Thomas Hoffmann et al. Two light emitting diodes for emitting light of different colors are connected in each segment back-to-back. Since the light emitting diodes are connected to conduct currents in opposite directions, it would be impossible to illuminate them simultaneously, because the opposite currents attempting to pass through a single conductor would cancel.

[0012] A system for measuring radioactivity is described in U.S. Pat. No. 2,643,344, issued on Jun. 23, 1953 to Ian H. McLaren et al. Another systems for measuring radioactivity are described in U.S. Pat. No. 2,648,015 issued on Aug. 4, 1953 to Alexander Greenfield et al., and in U.S. Pat. No. 2,682,000 issued on Jun. 22, 1954 to Joseph F. Clayton et al. Since these three patents are very similar, they are equally authoritative. The system for measuring radioactivity, disclosed in the three patents, includes an analog pointer indicator having three scales, with three associated colored light bulbs, for indicating which scale is applicable for the reading of the measured value. A mechanism for automatic range selection is provided, which is controlled by two solenoids, and which also controls the three associated colored light bulbs. In response to the range selection, one of the light bulbs illuminates the indicator face with a distinctive color to indicate which measurement scale is applicable.

[0013] A digital meter is disclosed in U.S. Pat. No. 2,889,518, issued on Jun. 2, 1959 to Harold R. Hudson et al. The digital meter includes a motor, a wheel counter rotatable by the motor, a potentiometer rotatable by the motor, and a mechanical sampler (vibrator). An unknown voltage is compared, by the sampler, with an instant reference voltage that appears on the wiper of the potentiometer. The motor keeps rotating the potentiometer until the unknown voltage is equal to the reference voltage. The rotation of the motor is then automatically stopped, which also stops the wheel counter, whose position numerically indicates the value of the measured voltage. The decimal point monochromatic lamps are placed between the wheels of the counter. One of the decimal point lamps is illuminated, by manually operated range switch, to indicate by its position the selected measurement range.

[0014] The prior art measuring instruments do not contemplate that the digital indications of two different measured values may be simultaneously exhibited on a single display device and distinguished by different colors.

[0015] In a broad sense, it is the principal object of this invention to provide an improved variable color digital measuring instrument.

[0016] It is still another object of the invention to provide a dual measuring system having a single light emitting diode display device for exhibiting both measurement results.

[0017] It is still another object of the invention to provide a variable color digital measuring system for distinguishing two digital indications of two different measured values by different colors.

[0018] It is still another object of the invention to provide a measuring system with a variable color digital display device controlled by two simultaneously applied color control signals.

[0019] In summary, a measuring system is disclosed for measuring two independent input signals and for providing two digital indications of the measured values of the two signals on a single variable color light emitting diode display device which includes a plurality of side by side positioned display elements.

[0020] The invention resides in the provision of a color control for simultaneously developing two color control signals, for illuminating the first digital indication in a first color, and for illuminating the second digital indication in a second color, in order to distinguish them comfortably. The two color control signals may be developed either by a technique of a continuously variable color control or by a technique of a step variable color control, as will be described in detail subsequently.

[0021] In the drawings in which are shown several possible embodiments of the invention,

[0022] FIG. 1 is a block diagram of a typical prior art monochromatic digital display system.

[0023] FIG. 2 is a generalized block diagram of a variable color digital display system for the practice of the present invention.

[0024] FIG. 3 is a block diagram of a step variable color display system.

[0025] FIG. 4 is a block diagram of a continuously variable color display system.

[0026] FIG. 5 is a block diagram of 2-primary color digital display.

[0027] FIG. 6 is a block diagram of 3-primary color digital display.

[0028] FIG. 7 is an enlarged detail of one digit of 2-primary color digital display.

[0029] FIG. 8 is an enlarged cross-sectional view of one display segment in FIG. 7, taken along the line 8—8.

[0030] FIG. 9 is an enlarged detail of one digit of 3-primary color digital display.

[0031] FIG. 10 is an enlarged cross-sectional view of one display segment in FIG. 9, taken along the line 10—10.

[0032] FIG. 11 is a schematic diagram of one digit of 2-primary color control circuit of this invention.

[0033] FIG. 12 is a schematic diagram of one digit of 3-primary color control circuit of this invention.

[0034] FIG. 13 is a block diagram of a color control logic circuit for controlling 2-primary color display.

[0035] FIG. 14 is a block diagram of a color control logic circuit for controlling 3-primary color display.

[0036] FIG. 15 is a schematic diagram of a color control logic circuit for controlling 2-primary color display.

[0037] FIG. 16 is a schematic diagram of a color control logic circuit for controlling 3-primary color display.

[0038] FIG. 17 is a simplified schematic diagram, similar to FIG. 11, showing how the number ‘7’ can be displayed in three different colors.

[0039] FIG. 18 is a simplified schematic diagram, similar to FIG. 12, showing how the number ‘1’ can be displayed in seven different colors.

[0040] FIG. 19 is a block diagram of 2-primary color 4-digit display.

[0041] FIG. 20 is a block diagram of 3-primary color 4-digit display.

[0042] FIG. 21 is a block diagram of a signal converter for 2-primary color display.

[0043] FIG. 22 is a block diagram of a signal converter for 3-primary color display.

[0044] FIG. 23 is a schematic diagram of a comparator circuit for 2-primary color display.

[0045] FIG. 24 is a graph showing the relationship between the inputs and outputs of the comparator circuit in FIG. 23.

[0046] FIG. 25 is a schematic diagram of a comparator circuit for 3-primary color display.

[0047] FIG. 26 is a graph showing the relationship between the inputs and outputs of the comparator circuit in FIG. 25.

[0048] FIG. 27 is a block diagram of a continuously variable color display system utilizing two primary colors.

[0049] FIG. 28 is a block diagram of a continuously variable color display system utilizing three primary colors.

[0050] FIG. 29 is an expanded block diagram of FIG. 27.

[0051] FIG. 30 is an expanded block diagram of FIG. 28.

[0052] FIG. 31 is a schematic diagram of a scaling circuit.

[0053] FIG. 32 is a schematic diagram of an A/D converter and memory combination of FIGS. 29 and 30.

[0054] FIG. 33 is a schematic diagram of a memory and color converter combination of FIG. 29.

[0055] FIG. 34 is a timing diagram of the circuit shown in FIG. 33.

[0056] FIG. 35 is a schematic diagram of a memory and color converter combination of FIG. 30.

[0057] FIG. 36 is a timing diagram of the circuit shown in FIG. 35.

[0058] FIG. 37 is a continuation of the timing diagram of FIG. 36.

[0059] FIG. 38 is a graphic representation of TABLE 1.

[0060] FIG. 39 is a graphic representation of TABLE 2.

[0061] FIG. 40 is a graph of the ICI chromaticity diagram.

[0062] FIG. 41 is a block diagram of a multimeter with variable color digital display.

[0063] FIG. 42 is a block diagram of a multimeter with multiplexed variable color digital display.

[0064] FIG. 43 is a block diagram of a digital multimeter with a display that can change color in accordance with external control.

[0065] FIG. 44 is a block diagram of a digital multimeter with a display that can change color in accordance with internal control.

[0066] FIG. 45 is a block diagram of a digital multimeter with a display that can change color in accordance with measurement quantity.

[0067] FIG. 46 is a block diagram of a digital multimeter with a display that can change color in accordance with measurement location.

[0068] FIG. 47 is a simplified schematic diagram of a variable color digital multimeter for measuring outputs of different transducers.

[0069] FIG. 48 is a simplified schematic diagram of a variable color digital multimeter for measuring signals from different locations.

[0070] FIG. 49 is a simplified schematic diagram of a variable color digital multimeter for measuring signals by different methods.

[0071] FIG. 50 is a simplified schematic diagram of a variable color digital thermometer.

[0072] FIG. 51 is a simplified schematic diagram of a digital ampermeter with variable color range indication.

[0073] FIG. 52 is a simplified schematic diagram of a digital voltmeter with variable color range indication.

[0074] FIG. 53 is a simplified schematic diagram of a digital ohmmeter with variable color range indication.

[0075] FIG. 54 is a detail of the multimeter shown in FIGS. 51, 52, and 53.

[0076] FIG. 55 is a simplified schematic diagram of a digital voltmeter for displaying positive and negative measurement results in respectively different colors.

[0077] FIG. 56 is a simplified schematic diagram of a variable color display system for displaying decimal numbers such that digits preceding and following the decimal point are displayed in respectively different colors.

[0078] FIG. 57 is a timing diagram of the circuit shown in FIG. 56.

[0079] FIG. 58 is a simplified schematic diagram of a variable color display system for displaying integers and decimal numbers in respectively different colors.

[0080] FIG. 59 is a block diagram of a variable color display device for selectively displaying output digital data from different digital devices in respectively different colors.

[0081] FIG. 60 is a simplified schematic diagram of a variable color digital barometer.

[0082] FIG. 61 is a simplified schematic diagram of a digital multimeter for displaying measurement results in accordance with time.

[0083] FIG. 62 is a block diagram of a variable color digital multimeter with comparator and memory.

[0084] FIG. 63 is a block diagram of a variable color digital multimeter with comparator and memory for high and low limits.

[0085] FIG. 64 is a block diagram of a variable color digital multimeter with comparator and memory for previous measurement values.

[0086] FIG. 65 is a block diagram of a variable color digital multimeter with memory for previous measurement errors.

[0087] FIG. 66 is a schematic diagram of a comparator with low and high measurement limits.

[0088] FIG. 67 is a schematic diagram of a comparator and error counter.

[0089] FIG. 68 is a detail of the comparator, error flip-flop, and color control combination.

[0090] FIG. 69 is a detail of the comparator, error memory, and color converter combination.

[0091] FIG. 70 is a detail of the low measurement limit memory and comparator combination.

[0092] FIG. 71 is a detail of the error counter and PROM combination.

[0093] FIG. 72 is a schematic diagram of a variable color digital multimeter with registered comparator for comparing instant measured values with previously stored ones.

[0094] FIG. 73 is a block diagram of a variable color digital multimeter with uniform color control for all display digits.

[0095] FIG. 74 is a block diagram of a variable color digital multimeter with independent color control for each display digit.

[0096] FIG. 75 is a block diagram of a dual digital voltmeter with single variable color digital display.

[0097] FIG. 76 is a block diagram of a variable color RMS digital voltmeter with variable color crest factor indication.

[0098] FIG. 77 is the RMS and crest factor chart.

[0099] FIG. 78 is an expanded block diagram of a crest factor converter with ratio producing circuit.

[0100] FIG. 79 is an expanded block diagram of a crest factor converter with precision divider.

[0101] FIG. 80 is a schematic diagram of an RMS-to-DC converter.

[0102] FIG. 81 is a schematic diagram of a peak detector.

[0103] FIG. 82 is an expanded block diagram of 2-primary color control for the crest factor converter.

[0104] FIG. 83 is an expanded block diagram of 3-primary color control for the crest factor converter.

[0105] FIG. 84 is an expanded block diagram of 2-primary color converter for the crest factor converter.

[0106] FIG. 85 is an expanded block diagram of 3-primary color converter for the crest factor converter.

[0107] FIG. 86 is a front view of a variable color digital multimeter of the present invention.

[0108] FIG. 87 is a block diagram of a variable color digital multimeter controlled by a microprocessor.

[0109] FIG. 88 is an expanded block diagram of a variable color digital multimeter for indicating front and rear measurements in different colors.

[0110] FIG. 89 is an expanded block diagram of a variable color digital multimeter for indicating DC, AC, and OHMS measurements in respectively different colors.

[0111] FIG. 90 is an expanded block diagram of a variable color digital multimeter for indicating measurements with filter and without filter in different colors.

[0112] Throughout the drawings, like characters indicate like parts.

[0113] In the tables which show examples of the relationship between an input voltage, memory contents, and resulting color in the color converter of the present invention,

[0114] TABLE 1 shows the characteristic of a step variable 2-primary color converter.

[0115] TABLE 2 shows a rainbow-like characteristic of a continuously variable 3-primary color converter.

[0116] Throughout the tables, memory addresses and data are expressed in a well known hexadecimal notation.

[0117] Referring now, more particularly, to the drawings, in FIG. 1 is shown a block diagram of a typical prior art digital display system which usually includes a device 10afor developing digital data, a suitable decoder 20 for converting the digital data into a displayable code, and a monochromatic digital display 30 for indicating the digital data visually.

[0118] As shown in FIG. 2, the present invention resides in the substitution of a commercially well known monochromatic digital display with a variable color digital display 40, and in the addition of a color control circuit 50 for controlling the color of display 40. The variable color digital display system of this invention can simultaneously indicate the values of two different quantities, from the outputs of respective devices 10b, 10c, by causing the value of the first quantity to be indicated on display 40 in digital format, and by controlling the color of display 40 in accordance with the value of the second quantity.

[0119] In FIG. 3 is shown a block diagram of another embodiment of a variable color digital display system of the present invention, characterized by a step variable color control circuit 51.

[0120] In FIG. 4 is shown a block diagram of still another embodiment of variable color digital display system, characterized by a continuously variable color control circuit 56.

[0121] In FIG. 5 is shown a block diagram of a 2-primary color display system including a commercially well known 7-segment display decoder driver 22, a variable color 7-segment display element 42, and a 2-primary color control logic circuit 52. The decoder driver 22 accepts a 4-bit BCD (binary coded decimal) code at its inputs A0, A1, A2, A3 and develops output drive signals at its outputs a, b, c, d, e, f, g, and DP (decimal point) to drive respective segments of 7-segment display element 42. The color control circuit 52 accepts color control logic signals at its inputs R (red), Y (yellow), and G (green) and develops at its outputs drive signals for red bus 5 and green bus 6, respectively, to illuminate display element 42 in a selected color.

[0122] In FIG. 6 is shown a block diagram of a 3-primary color display system including a 7-segment display decoder driver 22, variable color 7-segment display element 43, and a 3-primary color control logic circuit 53. The color control circuit 53 accepts color control logic signals at its inputs R (red), Y (yellow), G (green), BG (blue-green), B (blue), P (purple), and W (white) and develops at its outputs drive signals for red bus 5, green bus 6, and blue bus 7, respectively, to illuminate display element 43 in a selected color.

[0123] In FIG. 7, the 2-primary color display element includes seven elongated display segments a, b, c, d, e, f, and g, arranged in a conventional pattern, which may be selectively energized in different combinations to display the desired digits. 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.

[0124] In FIG. 8, red LED 2eand green LED 3eare placed on the base of a segment body 15awhich is filled with a transparent light scattering material 16. When forwardly biased, LEDs 2eand 3eemit 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 15a. The color of the composite light signal may be controlled by varying the portions of the red and green light signals.

[0125] In FIG. 9, each display segment of the 3-primary color display element includes a triad of LEDs: red LED 2, green LED 3, and blue LED 4, which are closely adjacent such that the light signals emitted therefrom are substantially superimposed upon one another to mix the colors.

[0126] In FIG. 10, red LED 2e, green LED 3e, and blue LED 4eare placed on the base of a segment body 15bwhich is filled with a transparent light scattering material 16. Red LEDs are typically manufactured by diffusing a p-n junction into a GaAsP epitaxial layer on a GaAs substrate; green LEDs typically use a GaP epitaxial layer on a GaP substrate; blue LEDs are typically made from SiC material.

[0127] When forwardly biased, LEDs 2e, 3e, and 4eemit light signals of red, green, and blue colors, respectively, which are scattered within transparent material 16, thereby blending the red, green, and blue light signals into a composite light signal that emerges at the upper surface of segment body 15b. The color of the composite light signal may be controlled by varying the portions of the red, green, and blue light signals.

[0128] Tn FIG. 11 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). 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 driver 23. The cathodes of all red LEDs 2a, 2b, 2c, 2d, 2e, 2f, 2g, and 2iare 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 3iare interconnected to a like common electric path referred to as a green bus 6.

[0129] The red bus 5 is connected to the output of a tri-state inverting buffer 63a, capable of sinking sufficient current to forwardly bias all red LEDs 2ato 2iin display element 42. The green bus 6 is connected to the output of a like buffer 63b. The two buffers 63a, 63bcan be simultaneously enabled by applying a low logic level signal to the input of inverter 64a, and disabled by applying a high logic level signal thereto. When buffers 63a, 63bare enabled, the conditions of red bus 5 and green bus 6 can be selectively controlled by applying suitable logic control signals to the bus control inputs RB (red bus) and GB (green bus), to illuminate display element 42 in a selected color. When the buffers 63a, 63bare disabled, both red bus 5 and green bus 6 are effectively disconnected to cause display element 42 to be completely extinguished.

[0130] In FIG. 12 is shown a schematic diagram of a 3-primary color common anodes 7-segment display element 43 which can selectively display digital fonts in different colors. The cathodes of all red, green, and blue LED triads in each display segment are interconnected and electrically connected to respective outputs of a commercially well known common anode 7-segment decoder driver 24. The anodes of all red LEDs 2a, 2b, 2c, 2d, 2e, 2f, and 2gare interconnected to form a common electric path referred to as a red bus 5. The anodes of all green LEDs 3a, 3b, 3c, 3d, 3e, 3f, and 3gare interconnected to form a like common electric path referred to as a green bus 6. The anodes of all blue LEDs 4a, 4b, 4c, 4d, 4e, 4f, and 4gare interconnected to form a like common electric path referred to as a blue bus 7.

[0131] The red bus 5 is connected to the output of a non-inverting tri-state buffer 62a, capable of sourcing sufficient current to illuminate all red LEDs 2ato 2gin display element 43. The green bus 6 is connected to the output of a like buffer 62b. The blue bus 7 is connected to the output of a like buffer 62c. The three buffers 62a, 62b, and 62ccan be simultaneously enabled, by applying a low logic level signal to the input of inverter 64b, and disabled by applying a high logic level signal thereto. When buffers 62a, 62b, and 62care enabled, the conditions of red bus 5, green bus 6, and blue bus 7 can be selectively controlled by applying valid combinations of logic level signals to the bus control inputs RB (red bus), GB (green bus), and BB (blue bus), to illuminate display element 43 in a selected color. When buffers 62a, 62b, and 62care disabled, red bus 5, green bus 6, and blue bus 7 are effectively disconnected to cause display element 43 to be completely extinguished.

[0132] In FIG. 13 is shown a logic circuit 69afor developing drive signals for red bus 5 and green bus 6, to control the color of display element 42 shown in FIG. 11. Two voltage levels, referred to as logic high and low, are used throughout the description of the digital circuits. The color of display element 42 may be controlled by applying valid combinations of logic level signals to its color control inputs R (red), Y (yellow), and G (green). The logic circuit 69acombines the input signals in a logic fashion and develops output drive signals RB (red bus) and GB (green bus), for activating red bus 5 and green bus 6, respectively, of display element 42.

[0133] In FIG. 14 is shown a like logic circuit 69bfor developing drive signals for red bus 5, green bus 6, and blue bus 7, to control the color of display element 43 shown in FIG. 12. The color of display element 43 may be controlled by applying valid combinations of logic level signals to its color control inputs B (blue), P (purple), BG (blue-green), G (green), Y (yellow), W (white), and R (red). The logic circuit 69bcombines the input signals in a logic fashion and develops output drive signals RB (red bus), GB (green bus), and BB (blue bus), for activating red bus 5, green bus 6, and blue bus 7, respectively, of display element 43.

[0134] Exemplary schematic diagrams of the color control logic circuits shown in FIGS. 15 and 16 consider active high logic levels, which means that only the selected color control input is maintained at a high logic level, while all remaining color control inputs are maintained at a low logic level. The circuit in FIG. 15 is a detail of the color control logic circuit 69aemploying 2-input logic OR gates 60aand 60b, interposed between the color control inputs R, Y, G and bus control outputs RB, GB, in a manner which will become more apparent from the description below. A like circuit in FIG. 16 is a detail of the color control logic circuit 69bemploying 4-input logic OR gates 61a, 61b, and 61csimilarly interposed between the color control inputs B, P, BG, G, Y, W, R and bus control outputs RB, GB, BB. It will be obvious to those skilled in the art that other types of logic devices may be effectively used.

[0135] The operation of display element 42 shown in FIG. 11 will be now explained by the example of illuminating a digit ‘7’ in three different colors. A simplified schematic diagram to facilitate the explanation is shown in FIG. 17. Any digit between 0 and 9 can be selectively displayed by applying the appropriate BCD code to the inputs A0, A1, A2, and A3 of common-cathode 7-segment decoder driver 23. The decoder driver 23 develops at its outputs a, b, c, d, e, f, g, and DP drive signals for energizing selected groups of the segments to thereby visually display the selected number, in a manner well known to those having ordinary skill in the art. To display decimal number ‘7’, a BCD code 0111 is applied to the inputs A0, A1, A2, and A3. The decoder driver 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, and g.

[0136] 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 60arises to a high logic level, thereby causing the output of buffer 63ato drop to a low logic level. The current flows from the output a of decoder driver 23, via red LED 2aand red bus 5, to current sinking output of buffer 63a. Similarly, the current flows from the output b of decoder driver 23, via red LED 2band red bus 5, to the output of buffer 63a. The current flows from the output c of decoder driver 23, via red LED 2cand 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 impression of a character ‘7’. The green LEDs 3a, 3b, 3cremain extinguished because the output of buffer 63bis at a high logic level, thereby disabling green bus 6.

[0137] 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 60brises to a high logic level, thereby causing the output of buffer 63bto drop to a low logic level. The current flows from the output a of decoder driver 23, via green LED 3aand green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder driver 23, via green LED 3band green bus 6, to the output of buffer 63b. The current flows from the output c of decoder driver 23, via green LED 3cand 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 2cremain extinguished because the output of buffer 63ais at a high logic level, thereby disabling red bus 5.

[0138] 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 60aand 60brise to a high logic level, thereby causing the outputs of both buffers 63aand 63bto drop to a low logic level. The current flows from the output a of decoder driver 23, via red LED 2aand red bus 5, to current sinking output of buffer 63a, and, via green LED 3aand green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder driver 23, via red LED 2band red bus 5, to the output of buffer 63a, and, via green LED 3band green bus 6, to the output of buffer 63b. The current flows from the output c of decoder driver 23, via red LED 2cand red bus 5, to the output of buffer 63a, and, via green LED 3cand 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.

[0139] The operation of display element 43 shown in FIG. 12 will be now explained by the example of illuminating a digit ‘1’ in seven different colors. A simplified schematic diagram to facilitate the explanation is shown in FIG. 18. To display decimal number ‘1’, a BCD code 0001 is applied to the inputs A0, A1, A2, and A3 of common anode 7-segment decoder driver 24. The decoder driver 24 develops low voltage levels at its outputs b and c, to illuminate equally designated segments b and c, and high voltage levels at all remaining outputs (not shown), to extinguish all remaining segments a, d, e, f, and g.

[0140] To illuminate display element 43 in red color, the color control input R is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the output of OR gate 61arises to a high logic level, thereby causing the output of buffer 62ato rise to a high logic level. Then current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. As a result, segments b and c illuminate in red color, thereby causing a visual impression of a character ‘1’. The green LEDs 3b, 3cand blue LEDs 4b, 4cremain extinguished because green bus 6 and blue bus 7 are disabled.

[0141] To illuminate display element 43 in green color, the color control input G is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the output of OR gate 61brises to a high logic level, thereby causing the output of buffer 62bto rise to a high logic level. The current flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. As a result, segments b and c illuminate in green color.

[0142] To illuminate display element 43 in blue color, the color control input B is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the output of OR gate 61crises to a high logic level, thereby causing the output of buffer 62cto rise to a high logic level. The current flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result, segments b and c illuminate in blue color.

[0143] To illuminate display element 43 in yellow color, the color control input Y is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61aand 61brise to a high logic level, thereby causing the outputs of buffers 62aand 62bto rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. The current also flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. As a result of blending light of red and green colors in each segment, the segments b and c illuminate in substantially yellow color.

[0144] To illuminate display element 43 in purple color, the color control input P is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61aand 61crise to a high logic level, thereby causing the outputs of buffers 62aand 62cto rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. The current also flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result of blending light of red and blue colors in each segment, segments b and c illuminate in substantially purple color.

[0145] To illuminate display element 43 in blue-green color, the color control input BG is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61band 61crise to a high logic level, thereby causing the outputs of buffers 62band 62cto rise to a high logic level. The current flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. The current also flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result of blending light of green and blue colors in each segment, segments b and c illuminate in substantially blue-green color.

[0146] To illuminate display element 43 in white color, the color control input W is raised to a high logic level, while all remaining color control inputs are maintained at a low logic level. As a result, the outputs of OR gates 61a, 61b, and 61crise to a high logic level, thereby causing the outputs of respective buffers 62a, 62b, and 62cto rise to a high logic level. The current flows from the output of buffer 62a, via red bus 5 and red LED 2b, to the output b of decoder driver 24, and, via red LED 2c, to the output c of decoder driver 24. The current also flows from the output of buffer 62b, via green bus 6 and green LED 3b, to the output b of decoder driver 24, and, via green LED 3c, to the output c of decoder driver 24. The current also flows from the output of buffer 62c, via blue bus 7 and blue LED 4b, to the output b of decoder driver 24, and, via blue LED 4c, to the output c of decoder driver 24. As a result of blending light of red, green, and blue colors in each segment, segments b and c illuminate in substantially white color.

[0147] Since the outputs of decoder driver 24 may be overloaded by driving a triad of LEDs in parallel in display element 43, rather than a single LED in a monochromatic display, it would be obvious to employ suitable buffers to drive respective color display segments (not shown).

[0148] To illustrate how the present invention can be utilized in a multi-element variable color display configuration, in FIG. 19 is shown a detail of the interconnection in a 2-primary color 4-digit display having display segments 1a, 1b, 1c, and 1darranged in a 7-segment font. The color control inputs R, Y, and G of color controls 52a, 52b, 52c, and 52dof all display elements 46a, 46b, 46c, and 46dare interconnected, respectively, and enable inputs E1, E2, E3, and E4 are used to control the conditions of respective display elements 46a, 46b, 46c, and 46d. A high logic level at the enable input E extinguishes the particular display element 46a, 46b, 46c, or 46d; a low logic level therein illuminates display element 46a, 46b, 46c, or 46din a color determined by the instant conditions of the color control inputs R, Y, and G.

[0149] In FIG. 20 is shown a like detail of the interconnection in a 3-primary color 4-digit display having display segments 1a, 1b, 1c, and 1darranged in a 7-segment font. Similarly, the color control inputs B, P, BC, G, Y, W, and R of color controls 53a, 53b, 53c, and 53dof all display elements 47a, 47b, 47c, and 47dare interconnected, and the conditions of respective display elements 47a, 47b, 47c, and 47dare controlled by enable inputs E1, E2, E3, and E4. A high logic level at the enable input E extinguishes the particular display element 47a, 47b, 47c, or 47d; a low logic level therein illuminates display element 47a, 47b, 47c, or 47din a color determined by the instant conditions of the color control inputs B, P, BG, G, Y, W, and R.

[0150] The exemplary color control circuits described herein will cooperate equally well with a multi-element variable color display constructed either in common cathodes or in common anodes configuration.

[0151] The enable inputs E1, E2, E3, E4 may be utilized to control the variable color multi-digit display in a multiplexed configuration, wherein the color codes for the display digits are presented in a sequence, one at a time, at a relatively fast rate, while the particular display digit is enabled.

[0152] In FIG. 21 is shown a block diagram of a signal converter for developing color control logic signals for 2-primary color display. The signal converter 85aaccepts at its input voltage from a variable analog voltage source 11 and develops at its outputs color control logic signals R, Y, G, having relation to the magnitude of instant input analog voltage, for controlling the color of variable color display element 42, shown in FIGS. 11 and 15, in accordance with the magnitude of input voltage.

[0153] In FIG. 22 is shown a block diagram of a like signal converter for developing color control logic signals for 3-primary color display. The signal converter 85baccepts at its inputs voltage from source 11 and develops output color control logic signals B, P, BG, G, Y, W, R, related to the magnitude of instant input analog voltage, for controlling the color of variable color display element 43, shown in FIGS. 12 and 16, in accordance with the magnitude of input voltage.

[0154] In FIG. 23, the output voltage of variable analog voltage source 11 is applied to interconnected inputs of two analog comparators 82a, 82b, in a classic ‘window’ comparator configuration. When the voltage developed by source 11 is lower than the low voltage limit Vlo, set by a potentiometer 92a, the output of comparator 82adrops to a low logic level, thereby forcing the output of inverter 65ato rise to a high logic level, to activate the color control logic input Y, to thereby illuminate display element 42, shown in FIGS. 11 and 15, in yellow color.

[0155] When the voltage developed by source 11 is higher than the high voltage limit Vhi, set by a potentiometer 92b, the output of comparator 82bdrops to a low logic level, thereby forcing the output of inverter 65bto rise to a high logic level, to activate the color control logic input R, to thereby illuminate display element 42 in red color.

[0156] When the voltage developed by source 11 is between the low voltage limit Vlo and high voltage limit Vhi, the outputs of comparators 82a, 82brise to a high logic level, thereby causing the output of AND gate 66 to rise to a high logic level, to activate the color control logic input G, to thereby illuminate display element 42 in green color.

[0157] FIG. 24 is a graph depicting the relationship between the input voltage of the comparator circuit shown in FIG. 23 and the color of the display element shown in FIG. 11. The display element illuminates in yellow color for the input voltage lower than the limit Vlo, in green color for the input voltage between the limits Vlo and Vhi, and in red color for the input voltage higher than the limit Vhi.

[0158] In FIG. 25, the output voltage of variable analog voltage source 11 is applied to interconnected ‘+’ inputs of six analog comparators 82c, 82d, 82e, 82f, 82g, 82h, connected in a well known ‘multiple aperture window’ configuration. There are six progressively increasing voltage limits V1 to V6, set by respective potentiometers 92cto 92h. The outputs of comparators 82cto 82hare respectively connected, via inverters 65cto 65h, to the inputs I1 to I7 of a priority encoder 67. Each of the inputs I1 to I7 has assigned a certain priority (from I1 being the lowest priority progressively to I7 being the highest one). The priority encoder 67 develops at its outputs 00, 01, 02 a code identifying the highest priority input activated. The outputs of encoder 67 are respectively connected, via inverters 65jto 65m, to the inputs A0, A1, A2 of a 3-to-8 line decoder 68, to decode the outputs of encoder 67 into seven mutually exclusive active logic low outputs Y1 to Y7. The outputs Y1 to Y7 are respectively connected, via inverters 65pto 65v, to the color control logic inputs B, P, BG, G, Y, W, R of display element 43 shown in FIGS. 12 and 16.

[0159] When the output voltage of source 11 is lower than the lowest voltage limit V1, the output of comparator 82cdrops to a low logic level, thereby activating the input I1 of priority encoder 67. The code 110 developed at the outputs 00, 01, 02 is inverted by inverters 65jto 65mto yield the code 001 which produces a low logic level at the output Y1, to force, via inverter 65p, the color control input B to a high logic level for causing display element 43 to illuminate in blue color.

[0160] When the output voltage of the source 11 is between the adjacent voltage limits, e.g., V4 and V5, the output of comparator 82frises to a high logic level, thereby activating the input I5 of priority encoder 67. The code 100 developed at the inputs of decoder 68 produces a high logic level at the color control logic input Y, and display element 43 illuminates in yellow color.

[0161] FIG. 26 is a graph depicting the relationship between the input voltage of the comparator circuit shown in FIG. 25 and the color of display element 42 shown in FIG. 12. The display element illuminates in blue color for the input voltage lower than the limit V1, in purple color for the input voltage between the limits V1 and V2, in blue-green color for the input voltage between the limits V2 and V3, in green color for the input voltage between the limits V3 and V4, in yellow color for the input voltage between the limits V4 and V5, in white color for the input voltage between the limits V5 and V6, and in red color for the input voltage higher than the limit V6.

[0162] It would be obvious to those having ordinary skill in the art, in the view of this disclosure, that the color sequences could be readily changed by differently interconnecting the outputs of the comparator circuit with the color control logic inputs of display element 43.

[0163] FIG. 27 is a block diagram of a 2-LED continuously variable color display system, which includes a device 10 for developing electric signals and 2-LED color converter 57 for controlling red bus 5 and green bus 6, respectively, of 2-LED variable color display element 42 in accordance with the electric signals.

[0164] FIG. 28 is a block diagram of a 3-LED continuously variable color display system which differs from the like system shown in FIG. 27 in that a 3-LED color converter circuit 58 is utilized to control red bus 5, green bus 6, and blue bus 7, respectively, of 3-LED variable color display element 43, in accordance with the electric signals developed by device 10.

[0165] The display system shown in FIG. 29 utilizes a scaling circuit 80awhich scales input analog voltage levels to a voltage range suitable for an A/D converter 74a, which in turn develops at its outputs a digital code having relation to the value of the input analog voltage. The output lines of A/D converter 74aare connected to the address inputs of a memory 76 having a plurality of addressable locations which contain data indicating the portions of red color for several different values of the input analog voltage. The output data of memory 76 are applied to the inputs of a color converter 57 which will develop control signals for red bus 5 and green bus 6, respectively, of variable color display element 42.

[0166] The display system shown in FIG. 30 utilizes a scaling circuit 80band an A/D converter 74bfor converting the instant value of an input analog voltage to a digital code. The outputs of A/D converter 74bare connected, in parallel, to the address inputs of memory 76a, which contains data indicating the portions of red color, to the address inputs of memory 76b, which contains data indicating the portions of green color, and to the address inputs of memory 76c, which contains data indicating the portions of blue color. The output data of memory 76aare applied to red color converter 59awhich will develop control signals for red bus 5 of variable color display element 43. The output data of memory 76bare applied to green color converter 59bwhich will develop control signals for green bus 6 of display element 43. The output data of memory 76care applied to blue color converter 59cwhich will develop control signals for blue bus 7 of display element 43.

[0167] FIG. 31 is a schematic diagram of a scaling circuit capable of shifting and amplifying the input voltage levels. The circuit utilizes two operational amplifiers 81aand 81bin a standard inverting configuration. The amplifier 81ais set for a unity gain by using resistors 90aand 90bof equal values; potentiometer 92ais adjusted to set a desired offset voltage. The amplifier 81bsets the gain by adjusting feedback potentiometer 92bto a desired value with respect to resistor 90c. As a result, an input voltage, which may vary between arbitrary limits Vlow and Vhigh, may be scaled and shifted to the range between 0 Volts and 9.961 Volts, to facilitate the use of a commercially available A/D converter.

[0168] FIG. 32 is a schematic diagram of an A/D (analog-to-digital) converter 75 which is capable of converting input analog voltage, applied via resistor 90eto its input Vin, to 8-bit digital data for addressing a memory 77. The conversion may be initiated from time to time by applying a short positive pulse 99ato the Blank and Convert input B&C. A/D converter 75 will thereafter perform a conversion of the instant input voltage to 8-bit data indicative of its value. When the conversion is completed, the Data Ready output DR drops to a low logic level, thereby indicating that the data are available at the outputs Bit 1 to Bit 8, which are directly connected to respective address inputs A0 to A7 of memory 77. When the DR output drops to a low logic level, the Chip Select input CS of memory 77 is activated, memory 77 is enabled, and the data, residing at the address selected by the instant output of A/D converter 75, will appear at its data outputs D0 to D7.

[0169] The description of the schematic diagram in FIG. 33 should be considered together with its accompanying timing diagram shown in FIG. 34. A clock signal 99bof a suitable frequency (e.g., 10 kHz), to provide a flicker-free display, is applied to the Clock Pulse inputs CP of 8-bit binary counters 71eand 71fto step them down. At the end of each counter cycle, which takes 256 clock cycles to complete, the Terminal Count output TC of counter 71edrops to a low logic level for one clock cycle, to thereby indicate that the lowest count was reached. The negative pulse 99cat the TC output of counter 71e, which is connected to the Parallel Load input PL of counter 71f, causes the instant data at the outputs of memory 76 to be loaded into counter 71f. The data at memory 76 represent the portion of red color; the portion of green color is complementary. The rising edge of the TC pulse 99ctriggers flip-flop 73 into its set condition wherein its output Q rises to a high logic level.

[0170] The counter 71fwill count down, from the loaded value, until it reaches zero count, at which moment its TC output drops to a low logic level. The negative pulse at the TC output of counter 71f, which is connected to the Clear Direct input CD of flip-flop 73, causes the latter to be reset and to remain in its reset condition until it is set again at the beginning of the next 256-count cycle. It is thus obvious that the Q output of flip-flop 73 is at a high logic level for a period of time proportional to the data initially loaded into counter 71f. The complementary output {overscore (Q)} a high logic level for a complementary period of time.

[0171] The Q and {overscore (Q)} outputs of flip-flop 73 are connected to red bus 5 and green bus 6, respectively, via suitable buffers 63aand 63b, shown in detail in FIG. 11, to respectively energize red bus 5 and green bus 6 for variable time periods, depending on the data stored in memory 76.

[0172] By referring now, more particularly, to the timing diagram shown in FIG. 34, in which the waveforms are compressed to facilitate the illustration, the EXAMPLE 1 considers the memory data ‘FD’, in a standard hexadecimal notation, to generate light of substantially red color. At the beginning of the counter cycle, pulse 99cloads data ‘FD’ into counter 71f. Simultaneously, flip-flop 73 is set by the rising edge of pulse 99c. The counter 71fwill be thereafter stepped down by clock pulses 99b, until it reaches zero count, 2 clock cycles before the end of the counter cycle. At that instant a short negative pulse 99dis produced at its output TC to reset flip-flop 73, which will remain reset for 2 clock cycles and will be set again by pulse 99cat the beginning of the next counter cycle, which will repeat the process. It is readily apparent that flip-flop 73 was set for 254 clock cycles, or about 99% of the time, and reset for 2 clock cycles, or about 1% of the time. Accordingly, red bus 5 of display element 42 is energized for about 99% of the time, and green bus 6 is energized for the remaining about 1% of the time. As a result, display element 42 illuminates in substantially red color.

[0173] The EXAMPLE 2 considers the memory data ‘02’ (HEX) to generate light of substantially green color. At the beginning of the counter cycle, data ‘02’ are loaded into counter 71f, and, simultaneously, flip-flop 73 is set. The counter 71fwill count down and will reach zero count after 2 clock cycles. At that instant it produces at its output TC a negative pulse 99eto reset flip-flop 73. It is readily apparent that flip-flop 73 was set for 2 clock cycles, or about 1% of the time, and reset for 254 clock cycles, or about 99% of the time. Accordingly, red bus 5 of display element 42 is energized for about 1% of the time, and green bus 6 is energized for the remaining about 99% of the time. As a result, display element 42 illuminates in substantially green color.

[0174] The EXAMPLE 3 considers the memory data ‘80’ (HEX) to generate light of substantially yellow color. At the beginning of the counter cycle, data ‘80’ are loaded into counter 71f, and, simultaneously, flip-flop 73 is set. The counter 71fwill count down and will reach zero count after 128 clock cycles. At that instant it produces at its output TC a negative pulse 99fto reset flip-flop 73. It is readily apparent that flip-flop 73 was set for 128 clock cycles, or about 50% of the time, and reset for 128 clock cycles, or about 50% of the time. Accordingly, red bus 5 of display element 42 is energized for about 50% of the time, and green bus 6 is energized for the remaining about 50% of the time. As a result of blending substantially equal portions of red and green colors, display element 42 illuminates in substantially yellow color.

[0175] The description of the schematic diagram of a 3-LED color converter in FIG. 35 should be considered together with its accompanying timing diagrams shown in FIGS. 36 and 37. A clock signal 99bis applied to the CP inputs of counters 71d, 71a, 71b, and 71cto step them down. Every 256 counts a negative pulse 99cis generated at the TC output of counter 71d, to load data into counters 71a, 71b, and 71cfrom respective memories 76a, 76b, and 76c, and to set flip-flops 73a, 73b, and 73c. The data in red memory 76arepresent the portions of red color, the data an green memory 76brepresent the portions of green color, and the data in blue memory 76crepresent the portions of blue color to be blended.

[0176] The counters 71a, 71b, and 71cwill count down, from the respective loaded values, until zero counts are reached. When the respective values of the loaded data are different, the length of time of the count-down is different for each counter 71a, 71b, and 71c. When a particular counter 71a, 71b, or 71creaches zero count, its TC output momentarily drops to a low logic level, to reset its associated flip-flop (red counter 71aresets its red flip-flop 73a, green counter 71bresets its associated green flip-flop 73b, and blue counter 71cresets its associated blue flip-flop 73c). Eventually, all three flip-flops 73a, 73b, and 73cwill be reset. The Q outputs of flip-flops 73a, 73b, and 73care connected to red bus 5, green bus 6, and blue bus 7, respectively, via suitable buffers 62a, 62b, and 62c, as shown in FIG. 12, to respectively energize red bus 5, green bus 6, and blue bus 7 for variable periods of time.

[0177] By referring now more particularly to the timing diagram shown in FIGS. 36 and 37, the EXAMPLE 4 considers red memory data ‘80’, green memory data ‘00’, and blue memory data ‘80’, all in hexadecimal notation, to generate light of substantially purple color. At the beginning of the counter cycle, pulse 99csimultaneously loads data ‘80’ from red memory 76ainto red counter 71a, data ‘00’ from green memory 76binto green counter 71b, and data ‘80’ from blue memory 76cinto blue counter 71c. The counters 71a, 71b, and 71cwill be thereafter stepped down. The red counter 71awill reach its zero count after 128 clock cycles; green counter 71bwill reach its zero count immediately; blue counter 71cwill reach its zero count after 128 clock cycles.

[0178] It is readily apparent that red flip-flop 73awas set for 128 clock cycles, or about 50% of the time, green flip-flop 73bwas never set, and blue flip-flop 73cwas set for 128 clock cycles, or about 50% of the time. Accordingly, red bus 5 of display element 43 is energized for about 50% of the time, green bus 6 is never energized, and blue bus 7 is energized for about 50% of the time. As a result of blending substantially equal portions of red and blue colors, display element 43 illuminates in substantially purple color.

[0179] The EXAMPLE 5 considers red memory data ‘00’, green memory data ‘80’, and blue memory data ‘80’, to generate light of substantially blue-green color. At the beginning of the counter cycle, data ‘00’ are loaded into red counter 71a, data ‘80’ are loaded into green counter 71b, and data ‘80’ are loaded into blue counter 71c. The red counter 71awill reach its zero count immediately, green counter 71bwill reach its zero count after 128 clock periods, and so will blue counter 71c.

[0180] The red flip-flop 73 a was never set, green flip-flop 73bwas set for 128 clock pulses, or about 50% of the time, and so was blue flip-flop 73c. Accordingly, green bus 6 of display element 43 is energized for about 50% of the time, and so is blue bus 7. As a result, display element 43 illuminates in substantially blue-green color.

[0181] The EXAMPLE 6 considers red memory data ‘40’, green memory data ‘40’, and blue memory data ‘80’, to generate light of substantially cyan color. At the beginning of the counter cycle, the data ‘40’ are loaded into red counter 71a, data ‘40’ are loaded into green counter 71b, and data ‘80’ are loaded into blue counter 71c. The red counter 71awill reach its zero count after 64 clock cycles, and so will green counter 71b. The blue counter 71cwill reach its zero count after 128 clock cycles.

[0182] The red flip-flop 73awas set for 64 clock cycles, or about 25% of the time, and so was green flip-flop 73b. The blue flip-flop 73cwas set for 128 clock cycles, or about 50% of the time. Accordingly, red bus 5 and green bus 6 of display element 43 are energized for about 25% of the time, and blue bus 7 is energized for about 50% of the time. As a result of blending about 50% of blue color, 25% of red color, and 25% of green color, display element 43 illuminates in substantially cyan color.

[0183] The EXAMPLE 7 considers red memory data ‘80’, green memory data ‘40’, and blue memory data ‘40 ’, to generate light of substantially magenta color. At the beginning of the counter cycle, the data ‘80’ are loaded into red counter 71a, data ‘40’ are loaded into green counter 71b, and data ‘40’0 are loaded into blue counter 71c. The red counter 71awill reach its zero count after 128 clock cycles, green counter 71bwill reach its zero count after 64 clock cycles, and so will blue counter 71c.

[0184] The red flip-flop 73awas set for 128 clock cycles, or about 50% of the time, green flip-flop 73band blue flip-flop 73cwere set for 64 clock cycles, or about 25% of the time. Accordingly, red bus 5 of display element 43 is energized for about 50% of the time, green bus 6 and blue bus 7 are energized for about 25% of the time. As a result, display element 43 illuminates in substantially magenta color.

[0185] By referring now more particularly to FIGS. 38 and 39, which are graphic representations of TABLES 1 and 2, respectively, the data at each memory address are digital representation of the portion of the particular primary color. All examples consider an 8-bit wide PROM (Programmable Read Only Memory). However, the principles of the invention could be applied to other types of memories.

[0186] In FIG. 38, RED PORTION indicates the portion of red primary color; GREEN PORTION indicates the portion of green primary color. The RED PORTION for a particular memory address was calculated by dividing the actual value of data residing at that address by the maximum possible data ‘FF’ (HEX). The GREEN PORTION for the same memory address is complementary; it was obtained by subtracting the calculated value of the RED PORTION from number 1.0.

[0187] In FIG. 38 is shown the characteristic of a 2-primary color converter, defined in TABLE 1, for developing color variable in steps: pure green for input voltages less than 0.625 V, substantially yellow for voltages between 1.25 V and 1.875 V, pure red for voltages between 2.5 V and 3.125 V, and of intermediate colors therebetween, this sequence being repeated three times over the voltage range.

[0188] In FIG. 39, RED PORTION indicates the portion of red primary color; GREEN PORTION indicates the portion of green primary color; BLUE PORTION indicates the portion of blue primary color. The RED PORTION for a particular memory address was calculated by dividing the value of red data residing at such address by the maximum possible data ‘FF’ (HEX). Similarly, the GREEN PORTION for that memory address was obtained by dividing the value of green data by ‘FF’ (HEX). The BLUE PORTION was obtained by dividing the value of blue data by ‘FF’ (HEX).

[0189] In FIG. 39 is shown the characteristic of 3-primary color converter, defined in TABLE 2, for developing color continuously variable from pure red, through substantially orange and yellow, pure green, pure blue, to substantially purple, in a rainbow-like fashion.

[0190] In the examples of the characteristics of color converters shown in TABLE 1 and TABLE 2, the data values stored in red memory 76a, green memory 76b, and blue memory 76care so designed that the sums of the red data, green data, and blue data are constant for all memory addresses, to provide uniform light intensities for all colors. It is further contemplated that data stored in red memory 76a, green memory 76b, and blue memory 76cmay be modified in order to compensate for different efficiencies of red, green, and blue LEDs. By way of an example, data values for a low efficiency LED may be proportionally incremented such that the time of energization is proportionally increased, to effectively provide equal luminances for LEDs of unequal efficiencies.

[0191] With reference to FIG. 40 there is shown the ICI (International Committee on Illumination) chromaticity diagram designed to specify a particular color in terms of x and y coordinates. Pure colors are located along the horseshoe-like periphery. Reference numbers along the periphery indicate wavelength in nanometers. When relative portions of three primary colors are known, the color of light produced by blending their emissions can be determined by examining the x and y values of ICI coordinates.

[0192] FIG. 41 is a generalized block diagram of a multimeter with variable color digital display which includes a multimeter 101 for measuring values of a QUANTITY 1, digital decoder driver 21 for converting the output data of multimeter 101 to a displayable code, and variable color digital display 40 for indicating the measured values in digital format. The invention resides in the addition of a color converter circuit 55 for converting values of a QUANTITY 2 to color control signals for controlling the color of display 40. The display 40 thus simultaneously indicates values of the QUANTITY 1, in digital format, and values of the QUANTITY 2, in variable color.

[0193] FIG. 42 is a generalized block diagram of a like multimeter system with a multiplexed variable color digital display 41, which differs from the diagram shown in FIG. 41 in that the multimeter 102 develops at its outputs multiplexed signals to directly drive display 41.

[0194] A digital multimeter shown in a block diagram configuration in FIG. 43 is capable of selectively setting certain of its external controls by an external control selector 121a. The invention resides in the addition of associated color selector 121bfor causing variable color digital display 40 to illuminate in a color corresponding to the selected external control. The measurements performed with different external controls may be displayed in respectively different colors. The selectors 121a, 121bmay include relays, mechanical switches, electronic and optical elements, devices for executing program of instructions, and the like. The association between the selectors 121aand 121bmay be, in its simplest form, a direct coupling, whereby the selector 121bis always in the same position as the selector 121a, or a more sophisticated association in space, time, hardware, and software. The external controls may comprise measurement modes, such are local, remote, 2-wire, and 4-wire; measurement functions, such are DC voltage, AC voltage, DC current, AC current, resistance, capacitance, and inductance; measurement ranges for selectively scaling measured signals, and the like.

[0195] In FIG. 44 is shown a block diagram of a like digital multimeter capable of selectively setting certain of its internal measurement controls by an internal control selector 121a. The associated color selector 121bcauses display 40 to illuminate in a color corresponding to the selected internal control, such that the measurements performed with different internal controls may be displayed in respectively different colors. The internal controls may comprise measurement modifiers, such are single, continuous, synchronous, and asynchronous triggering, sample rate, filter, offset, external reference, and scaling; measurement methods, units, and the like.

[0196] FIG. 45 is a block diagram of a digital multimeter with measurement quantity selection. By way of an example, when the quantity selector 121ais in its second position, thereby selecting the QUANTITY 2 to the input of digital multimeter 103, the associated color selector 121bis also in its second position, thereby applying the control voltage to the color control input C2, to cause the measured values of the QUANTITY 2 to be indicated on display 40 in the color C2. The measurements of different quantities may be indicated in respectively different colors.

[0197] FIG. 46 is a block diagram of a digital multimeter with input location selection. By way of an example, when the location selector 121ais in its third position, thereby selecting for the input of multimeter 103 signals from the LOCATION 3, the associated color selector 121bis also in its third position, thereby applying the control voltage to the color control input C3, to cause the measured values from the LOCATION 3 to be indicated on display 40 in the color C3. The measurements from different locations may be indicated in respectively different colors.

[0198] In FIG. 47 is shown an exemplary simplified schematic diagram of a digital multimeter for selectively measuring values of several different quantities from outputs of a temperature transducer 172, which converts temperature to voltage, pressure transducer 173, which converts atmospheric pressure to voltage, and physiological transducer 174, which converts physiological information to voltage. The term transducer, as used throughout the description of the invention, is used in its widest sense so as to include every type of a device for performing a conversion of one form of energy to another. The principles of the invention may be applied to various displacement, motion, force, pressure, sound, flow, temperature, humidity, weight, magnetic, and physiological transducers, and the like. When switch 123gis in its first position, thereby selecting temperature transducer 172, digital voltmeter 108 measures the output voltage of transducer 172, which is proportional to ambient temperature, and display 48 indicates the measured temperature in digital format. The associated switch 123his also in its first position, thereby connecting the control voltage +VCC to the color control input C1 of the color control circuit 42, to cause the display 48 to illuminate in the color C1. When switch 123gis in its second position, thereby selecting pressure transducer 173, display 48 indicates the measured atmospheric pressure in digital format and in the color C2. When switch 123gis in its last position, thereby selecting physiological transducer 174, display 48 indicates the measured physiological information, such as blood pressure, heart beat, and the like, in digital format and in the color Cn. Measured values of different quantities are thus displayed in respectively different colors.

[0199] In FIG. 48 is shown an exemplary simplified schematic diagram of a digital multimeter capable of measuring signals from seven different locations and of indicating the measured results in seven different colors, respectively. The outputs Q0, Q1, Q2 of a 4-bit binary counter 162b, which may be from time to time incremented by a clock pulse, are connected, in parallel, to the address inputs A, B, C of analog multiplexers 147a, 147b, respectively, to cause the multiplexer 147ato internally route signals from its selected input, e.g., Y1, to its output Y, and, simultaneously, to apply 1the control voltage +VCC from the terminal Y of multiplexer 147b, via its selected terminal, e.g., Y1, to one of the color control inputs B to R. The measured signals from the selected location are indicated on display 40 in digital format and in a color unique to the selected location. The indicated color sequences are merely exemplary; it would be obvious to devise other color sequences by differently interconnecting the terminals Y1 to Y7 of multiplexer 147bwith the color control inputs.

[0200] In FIG. 49 is shown a simplified schematic diagram of an AC digital voltmeter for selectively measuring an RMS (Root Mean Square) or MAV (Mean Average Value) of a measured waveform. An RMS measurement provides a power content of the measured signal, as will be more fully explained later, for a waveform of any shape. Since the MAV measured value may differ from the RMS value for certain waveform shapes, it would be desirable to know which measurement method is employed. A switch 123iselects either the output of RMS converter 181 or the output of the precision rectifier circuit, consisting of an op amp 159a, resistors 124x, 124y, 124zand diodes 128a, 128b, to the input of digital voltmeter 108. An associated switch 123jselects one of the color control inputs C1, C2, in accordance with the selection of the measurement method. The display 48 indicates the magnitude of the measured AC waveform in digital format and in a color unique to the selected measurement method.

[0201] In FIG. 50 is shown a simplified schematic diagram of a digital thermometer which can selectively measure temperature in the Kelvin, Celsius, or Fahrenheit scale, by connecting the output of one of temperature transducers 177, 178, 179, via a switch 123m, to the input of digital voltmeter 108. An associated switch 123napplies the control voltage +VCC to one of the color control inputs C1, C2, C3, of the color control circuit 52, to thereby illuminate display 48 in a color unique to the selected temperature scale. The output voltage of Kelvin temperature transducer 177 is linearly proportional to temperature in the Kelvin scale. The output voltage of like Celsius temperature transducer 178 is linearly proportional to temperature in the Celsius scale. The output voltage of like Fahrenheit temperature transducer 179 is linearly proportional to temperature in the Fahrenheit scale.

[0202] In FIG. 51 is shown a simplified schematic diagram of a digital ampermeter with variable color range indication. The precision shunt resistors 126a, 126b, 126c, 126d, 126e, connected in series, convert measured current to voltage, which is applied, via a resistor 125fof suitable value, to the input terminal of digital voltmeter 108. The current range is selectable by a rotary switch 123a, in a manner well known to those skilled in the art. The invention resides in the addition of a second rotary switch 123b, associated with the switch 123asuch that both switches are always in the same position, to connect the reference voltage +VCC to the selected one of the color control inputs, in accordance with the selected current range. The remaining color control inputs are tied to ground via suitable pull down resistors 125a, 125b, 125c, 125d, 125e. By way of an example, display 40 may indicate measured current values on the 0.2 mA range in blue color, on 2 mA range in purple color, on 20 mA range in green color, on 200 mA range in yellow color, and on 2 A range in red color.

[0203] In FIG. 52 is shown a simplified schematic diagram of a digital voltmeter with variable color range indication. The precision voltage attenuating resistors 126f, 126g, 126h, 126i, 126jare connected in series, and the voltage range is selected by a rotary switch 123c, in a manner well understood by those skilled in the art. The invention resides in the addition of a second rotary switch 123d, associated with the switch 123c, to apply the reference voltage +VCC to the selected color control input. By way of an example, display 40 may indicate measured values on the 0.2 V range in white color, on 2 V range in yellow color, on 20 V range in green color, on 200 V range in blue-green color, and on 2000 V range in red color.

[0204] In FIG. 53 is shown a simplified schematic diagram of a digital ohmmeter with variable color range indication. The precision standard resistors 126k, 126m, 126n, 126p, 126r, selectable by a rotary range switch 123e, are connected such that the selected one of the standard resistors is in series with the measured resistance Rx, in a well known ratiometric arrangement. The invention resides in the addition of a second switch 123f, associated with the switch 123e, to connect the reference voltage +VCC to the selected one of the color control inputs, in accordance with the selected resistance range. By way of an example, display 40 may indicate measured resistance values on the 0.1 k range in yellow color, on 1 k range in green color, on 10 k range in blue color, on 100 k range in purple color, and on 1 M range in red color.

[0205] The examples of range and precision resistor values shown in FIGS. 51, 52, 53 should be considered merely as exemplary. Although the switches 123 are shown as rotary switches, they may, alternatively, be of any other type, such are pushbutton switches and relay contacts. Another modification envisions that only certain of the display digits may change color in accordance with the measurement range, while the remaining display digits may change color in accordance with a different quantity. It is readily apparent that the principles of the invention may be effectively applied to autoranging multimeters.

[0206] In FIG. 54 is shown a detail of the multimeter of FIGS. 51, 52, 53 which includes a DVM chip 108 capable of converting analog voltage applied to its inputs HI and LO into signals for directly driving respective segments of a 3½ digit 7-segment variable color display 48. The color control 50 causes display 48 to illuminate in a selected color, as described previously.

[0207] Commercially known digital multimeters are capable of indicating negative measured results, by displaying a small negative sign at the most significant digit, and positive measured results, usually by not displaying the minus sign. When a series of measurements is performed, it is difficult to distinguish between the positive and negative measurement results displayed on a long character string, particularly when the measurements are performed at a relatively fast rate. In FIG. 55 is shown how this problem may be effectively solved by displaying positive and negative measurement results in respectively different colors on a 3½ digit common cathodes variable color display 48, which is capable of displaying a minus sign by illuminating the segment g in the most significant digit. The polarity output POL of digital voltmeter 108 is directly connected to the color control input R, and, via an inverter 151a, to the color control input G, of the color control circuit 52. When the POL output is at a low logic level, to indicate that the displayed number is positive, the minus sign is extinguished. A low logic level at the POL output forces the output of the inverter 151ato rise to a high logic level, to activate the color control input G, to thereby illuminate display 48 in green color. When the POL output rises to a high logic level, to indicate that the displayed number is negative, the minus sign is illuminated. A high logic level at the POL output activates the color control input R, to thereby illuminate display 48 in red color. It would be obvious, in the view of the present disclosure, to devise other color combinations.

[0208] The description of a variable color digital display system shown in FIG. 56, 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 shown in FIG. 57. The display system, which in its exemplary embodiment utilizes eight single-digit variable color displays 46ato 46h, which are only partially shown, is capable of detecting the position of decimal point in a string of displayed digits and of displaying all digits that precede the decimal point in a first color and all digits that follow the decimal point in a second color. The decimal point outputs DP of common-cathodes 7-segment decoders 23ato 23h, which may receive displayable data in a conventional manner (not shown), are continuously scanned in a sequence by a multiplexer 146 which is incremented by a counter 162ddriven by clock 199jof a suitable frequency. When an active high DP output is detected on certain of the decoders 23ato 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 138bto 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. 57 in the line designated F—F 138jQ OUTPUT at waveform 199p, the position of the detected decimal point in reference to the scanning cycle. A decoder 166 is incremented synchronously with the 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 138bto 138hto states determined by the conditions of their D inputs, respectively, at the time of triggering, as may be best observed in FIG. 57 in the lines designated DEC 166 OUTPUTS Y0 to Y7 at waveforms 190ato 199h. All flip-flops 138bto 138h, which were triggered before the decimal point was located during the scanning cycle, are triggered to their reset states, while all remaining flip-flops 138bto 138h, which were triggered after the decimal point was located, are triggered to their set states. The Y7 output of the decoder 166 is connected to the clear direct input CD of the DP flip-flop 138j, to force the latter to its reset condition at the end of each scanning cycle. The outputs Q and {overscore (Q)} of flip-flops 138bto 138hare respectively connected to color control inputs R and G of the color control circuits 52bto 52h, to thereby cause all display digits 46bto 46hthat precede the instant decimal point to be illuminated in green color, and all remaining display digits that follow the decimal point to be illuminated in red color. It would be obvious that other color combinations may be devised.

[0209] The display system shown in FIG. 58 is capable of detecting the presence or absence of decimal point in the displayed digital string, and accordingly of displaying digital strings with decimal point (decimal numbers) in a first color, and digital strings without decimal point (integers) in a different color. The decimal point outputs DP of all common-cathode 7-segment decoders 23ato 23hare respectively connected to the inputs of an OR gate 154. When decimal point is present in the displayed digital string, the appropriate DP output rises to a high logic level, thereby forcing the non-inverting output of OR gate 154, which is connected to interconnected color control inputs R of all color control circuits 52ato 52h, to rise to a high logic level, to thereby cause all displays 46ato 46hto illuminate in red color. When no decimal point is detected in the displayed digital string, the inverting output of OR gate 154, which is connected to interconnected color control inputs G of all color control circuits 52ato 52h, rises to a high logic level, to thereby cause all displays 46ato 46hto illuminate in green color.

[0210] In FIG. 59 is shown a block diagram of a variable color digital display system for selectively indicating output values of seven digital devices 12ato 12gin digital format and in respectively different colors. The outputs of digital devices 12ato 12gare respectively connected to the inputs I1 to I7 of a digital multiplexer 146b, which is addressed by a counter 161c. Displayable digital data are routed from one of the multiplexer's inputs, selected by the instant output code of counter 161c, to its output Z and to variable color digital display element 43, to be displayed thereon in digital format. The counter 161csimultaneously addresses color decoder 165a, to activate one of seven color control inputs B, P, BG, G, Y, W, R of color control circuit 53, in accordance with the selected input of multiplexer 146b. By way of an example, when the counter's output code 010 (binary) is applied to the address inputs of multiplexer 146b, the input I2 is selected, and data from digital device 12bare indicated on display element 43 in digital format. Simultaneously, the counter's output code causes the output Y2 of decoder 165ato be active, thereby activating the color control input P, to cause display element 43 to illuminate in purple color. Digital devices 12ato 12gmay include certain of those disclosed earlier.

[0211] In FIG. 60 is shown an expanded block diagram of a variable color digital barometer with memory, for indicating measured values of atmospheric pressure in digital format and in a color depending on previous measured values. A scaling circuit consisting of op amps 159c, 159dand resistors 124a, 124b, 124c, 124d, 124eshifts and scales output voltage of a pressure transducer 176, which is linearly proportional to atmospheric pressure, such that voltage at the input of digital voltmeter 107 directly corresponds to the atmospheric pressure, either in milibars or in mm Hg, depending on the values of resistor 124eand V REF voltage. The digital voltmeter 107 converts the instant analog voltage at its input to a digital code which is simultaneously applied to variable color digital display 40, to be indicated thereon in digital format, and to the data input of a combined memory and comparator 144, to be stored therein from time to time. The invention resides in the addition of a color control circuit 50 for illuminating display 40 in a color depending on the result of comparison between the instant measured value of atmospheric pressure and previously stored one, to thereby indicate whether the atmospheric pressure is either rising, or falling, or remains unchanged. A three-decade counter 164, or other suitable device for keeping time, is incremented in regular intervals by a clock, and its DIGITS outputs indicate the instant count. A decoder 165bhas its ADDRESS inputs connected, in a rather simplified manner, to the counter's DIGITS outputs and utilizes the counter's SELECT output as a strobe. As a result of continuous counting, at regular time intervals there will appear relatively short pulses 99mat the selected decoder's output Yn, which is connected to the LOAD input of memory and comparator 144, to load the instant output data of digital voltmeter 107 into memory 144. The comparator 144 effects a comparison of the data currently stored in its memory with the instant output data of digital voltmeter 107 and accordingly develops output signals LT (Less Than), EQ (Equal), and GT (Greater Than). The comparator's outputs LT, EQ, GT are respectively connected to the color control inputs R, Y, G of color control circuit 50, to cause display 40 to illuminate in red color when the comparator's output LT is active (atmospheric pressure is falling), in yellow color when the output EQ is active (atmospheric pressure is unchanged), and in green color when the output GT is active (atmospheric pressure is rising). The above description may serve as a background for consideration of more sophisticated barometric systems capable of comparing the instant measured values with values obtained by virtue of arithmetic and logic operations, such are average or peak values of previous measurements, and of displaying measured values in a variety of colors depending on the rate of increase or decrease of measured values.

[0212] In FIG. 61 is shown a block diagram of a digital multimeter 103 for making series of measurements in combination with a clock 148 for keeping time. The time signals developed by the clock circuit 148 are decoded by a suitable time decoder 168 and converted to color control signals C1, C2 to Cn. The values measured by the multimeter 103 are indicated on display 40 in digital format and in a color having relation to time.

[0213] FlG. 62 is a block diagram of a multimeter which includes a memory 131, containing a reference measured value, and a comparator 141. Measured values of input signal, which is applied to an input conditioning circuit 120, wherein it may be switched, scaled, attenuated, rectified, and filtered (not shown), are compared with the reference value stored in memory 131 and indicated on display 40 in digital format and in a color depending on the relationship between the measured value and the reference one. The memory 131 may include electronic storage elements, such are flip-flops, latches, RAMs, ROMs, and the like, and mechanical storage elements, such are binary switches or the like. When the instant measured value is less than the reference value, the output ‘<’ of the comparator 141 is active, thereby activating the color control input C2 of the color control circuit 50, to illuminate display 40 in the color C2. When the instant measured value is greater than the reference one, the comparator's output ‘>’ is active, and the measured value is displayed in the color C1. Alternatively, the instant measured value may be displayed in a color indicating its deviation, absolute or relative, from the reference value.

[0214] FIG. 63 is a block diagram of a multimeter which includes a memory 131afor storing a low measurement limit, memory 131bfor storing a high measurement limit, and comparators 141a, 141b. The measured values are compared with the high and low measurement limits and are indicated on display 40 in digital format and in a color depending on the relationship between the measured value and the low and high measurement limits. When the measured value is lower than the low measurement limit, stored in memory 131a, the output ‘<’ of the comparator 141ais active, thereby activating the color control input C3 of the color control circuit 50, to illuminate display 40 in the color C3. When the measurement value is higher that the high measurement limit, stored in memory 131b, the output ‘>’ of comparator 141bis active, thereby activating the color control input C1, to illuminate display 40 in the color C1. When the measured value is higher than the low measurement limit and lower than the high measurement limit, the active outputs ‘>’ of the comparator 141aand ‘<’ of the comparator 141bare combined in a logic fashion by a logic circuit 150, thereby activating the color control input C2, to illuminate display 40 in the color C2.

[0215] FIG. 64 is a block diagram of a multimeter for making repeated measurements, which includes an A/D converter 106 and memory & comparator circuit 144. The instant measured value of the input signal, converted to digital format by the A/D converter 106, may be from time to time stored in memory 144, so that subsequent measurements could be compared with the stored values. The instant measured value is displayed on display 40 in digital format and in a color depending on the result of comparison with the value stored in the memory. When the instant measured value is less than that stored in the memory, the output LT (Less Than) of comparator 144 is active, thereby activating the color control input C3 of color control circuit 50, to display the measured value in the color C3. When the instant measured value is equal to that stored in the memory, the comparator output EQ (Equal) is active, thereby activating the color control input C2, to display the measured value in the color C2. When the instant measured value is greater than that stored in the memory, the comparator output GT (Greater Than) is active, thereby activating the color control input C1, to display the measured value in the color C1.

[0216] FIG. 65 is a block diagram of a multimeter for making a series of measurements and for comparing each measured value, by comparators 141a, 141b, with low and high measurement limits stored in memories 131a, 131b, respectively. An additional error memory 131c, which may include an error counter, and logic circuit 150aare provided for storing the number of measurement errors. The instant measured value is indicated on display 40 in digital format and in a color depending, firstly, on its relationship with the applicable low and high measurement limits, and, secondly, on the number of previous measurement errors. Various kinds of decisions may be made, by a logic circuit 150b, based on the contents of the error memory. The decisions may be as simple as merely to display the measurement results in the color C1 for no previous measurement errors and in the color C2 for some previous errors, or may involve sophisticated color selections based on the number of previous errors and total number of measurements, arrived at by virtue of arithmetic and logic operations.

[0217] In FIG. 66 is shown an exemplary simplified schematic diagram of the limit memory and limit comparator combination, generally shown in FIG. 65, for 8-bit measurement data (two BCD digits). The 8-bit data stored in a memory 132a, symbolizing the low measurement limit, are applied to respective inputs B0 to B7 of a digital comparator 143a; the 8-bit data stored in a like memory 132b, symbolizing the high measurement limit, are applied to respective inputs B0 to B7 of a comparator 143b. The 8-bit measurement data, having relation to the instant measured value, are applied to respective inputs A0 to A7 of both comparators 143a, 143b, interconnected in parallel. The comparators 143a, 143beffect a comparison between the measurement data and the instant low and high measurement limits and accordingly develop their output signals ‘<’, ‘=’, ‘>’. When the instant measurement data are less than the low measurement limit, the ‘<’ output of the comparator 143arises to a high logic level. When the instant measurement data are greater than the high measurement limit, the ‘>’ output of the comparator 143brises to a high logic level. When the instant measurement data are between the low and high measurement limits, one of the inputs of each OR gate 152a, 152brises to a high logic level, thereby forcing both inputs of AND gate 155ato rise to a high logic level, which in turn forces the output of the latter to rise to a high logic level. The outputs PASS, FAIL LOW LIMIT, and FAIL HIGH LIMIT may be connected to respective inputs C1, C2, and C3 of the color control 50. By way of an example, display 40 may illuminate in green color for pass, in yellow color for fail on the low limit, and in red color for fail on the high limit.

[0218] In FIG. 67 is shown a simplified schematic diagram of the limit memory, limit comparator, and error memory combination, in a digital multimeter for making a series of measurements. A memory 132ccontains data symbolizing low measurement limits for each measurement step. A like memory 132dcontains data symbolizing high measurement limits for each measurement step. An 8-bit counter 161, which is incremented for each measurement step by a suitable clock pulse, is used to simultaneously address both memories 132c, 132d. When addressed for a particular measurement step, the memories 132c, 132dpresent the data residing at such address to the inputs B0, to B7 of comparators 143c, 143d, respectively, as the instant low and high measurement limits. The comparison of the instant measurement data with the instant measurement limits is performed by comparators 143c, 143dat each measurement step. When the measurement passes, the PASS output rises to a high logic level. When the measurement fails, either on the low or high measurement limit, the FAIL output of OR gate 152erises to a high logic level, and error memory 135ais incremented by the next clock pulse. Thus the error memory 135acontains data representing the total number of measurement errors. A logic circuit 150bconverts the instant error memory data to color control signals C2 to Cn, whereby the instant measured value is displayed in the color C1 on pass, and in a certain of the colors C2 to Cn on fail, depending on the total number of previous measurement errors, as will be more fully explained later.

[0219] In FIG. 68 is shown a detail of the comparator, error flip-flop, and color control combination generally shown in FIG. 65. When a measurement error occurs, either on the low or high measurement limit, the output of an OR gate 152f, which is connected to the D input of error flip-flop 138a, rises to a high logic level, and the error flip-flip will be set by the next clock pulse, to indicate that there was a measurement error. The error flip-flop may be suitably reset (not shown), e.g., at the beginning of each measurement series. Results of the measurements are indicated on display 40 in digital format and in a color depending on the result of comparison with the instant low and high measurement limits and on the condition of the error flip-flop. By way of an example, the measurements may be displayed in green color on pass, in yellow color on fail with no previous measurement errors, and in red color on fail with previous measurement errors.

[0220] FIG. 69 is another exemplary detail of the comparator, error memory, and color converter combination generally shown in FIG. 67. When a measurement error occurs, the output of an OR gate 152g, which is connected to the DATA input of the error memory 135b, rises to a high logic level, and the error memory contents will be incremented by the next clock pulse. The error memory 135bthus contains data indicating the total number of previous measurement errors. The outputs of error memory 135bare applied to interconnected inputs of red color converter 59a, green color converter 59b, and blue color converter 59c, which develop drive signals for energizing red bus 5, green bus 6, and blue bus 7 of display 40 to illuminate it in a color related to the total number of previous errors.

[0221] FIG. 70 is a detail of the low limit memory and comparator combination shown in FIG. 66. An 8-bit latch 134 stores data representing the instant low measurement limit, which may be from time to time entered via its inputs D0 to D7 (not shown). Two 4-bit digital comparators 142a, 142bare cascaded to form an 8-bit digital comparator, in a manner well understood by those skilled in the art.

[0222] FIG. 71 is an exemplary detail of the error counter and PROM combination shown in FIG. 69. An 8-bit counter 163, which contains the count indicating the total number of previous measurement errors, is employed to address, via its outputs Q0 to Q7, a PROM 77 containing the color conversion data which may be used to develop drive signals for red bus 5, green bus 6, and blue bus 7, as previously shown in FIG. 35, to thereby illuminate display 40 in a color depending on the total number of previous measurement errors.

[0223] The schematic diagram shown in FIG. 72 includes a digital multimeter 103 for making repeated measurements of input signals and for developing at its outputs a 4-digit BCD code having relation to the magnitude of the instant input signal, and two cascaded registered comparators 145a, 145bfor comparing the instant measured value with the value previously stored. From time to time, a short positive pulse 99nmay be applied to interconnected Load inputs S0, S1, to cause the instant data at the inputs I0 to I7 of both registered comparators 145a, 145bto be loaded therein. The subsequent measured values will be compared with the reference value currently loaded in the register, and interconnected outputs LT (Less Than), EQ (Equal), GT (Greater Than), which are tied to the supply voltage via suitable pull-up resistors 124f, 124g, 124h, will indicate the result of each comparison. The comparator outputs are respectively connected to the color control inputs C1, C2, C3 of the color control circuit 50, to control the color of display 40, shown in FIG. 62, in accordance with the result of the comparison. The display 40 indicates the instant measured value in digital format and in a color depending on the result of comparison with the reference value currently stored in the register. By way of an example, display 40 may illuminate in green color when the instant measured value is equal to the reference value, in yellow color when it is less than the reference value, and in red color when it is larger than the reference value.

[0224] In FIG. 73 is shown a simplified schematic diagram of a digital voltmeter with 3½ digit variable color display. The digital voltmeter 107 is configured, by having its initialize conversion input INIT connected to a high logic level, to continuously convert input analog voltage, applied to its input terminal via a resistor 124a, to 3½ digit BCD code corresponding to the magnitude of instant input voltage. The BCD codes for the respective digits are converted, by 7-segment decoders 22a, 22b, 22c, 22d, to signals for directly energizing the segments of the variable color display digits 42a, 42b, 42c, 42d, respectively, in a manner well understood by those skilled in the art. The color control circuit 50 causes all four display digits to illuminate uniformly in a selected color, as previously described.

[0225] A like block diagram shown in FIG. 74 differs in that four color control circuits 50a, 50b, 50c, 50dare employed to independently control the colors of respective display digits 42a, 42b, 42c, 42d.

[0226] In FIG. 75 is shown, in a block diagram configuration, a multimeter utilizing two digital voltmeters 109aand 109bfor measuring respective INPUT SIGNALS 1 and 2. The measured values of both input signals are simultaneously indicated on a single 8-digit variable color display element 42 such that the four most significant display digits D1 to D4 indicate the output of digital voltmeter 109a, and the four least significant display digits D5 to D8 indicate the output of digital voltmeter 109b. In order to clearly distinguish between the two measured values, without the need for a visual gap therebetween, the color control circuit 52ais adapted, by having its color control input G connected to a high logic level, to illuminate the four most significant display digits D1 to D4 in green color, and like color control circuit 52bis adapted, by having its color control input R connected to a high logic level, to illuminate the four least significant digits D5 to D8 in red color.

[0227] FIG. 76 is a block diagram of an RMS digital voltmeter with variable color crest factor indication. The RMS (Root Mean Square) value of the measured waveform is its heating value when applied to a resistor; it indicates the magnitude of the measured waveform regardless of its shape. The Crest Factor is the peak signal value divided by the RMS value; it indicates what type of a waveform it is.

[0228] The digital voltmeter includes an RMS converter 181 for converting an input measured signal to a DC value representative of the energy content of the measured signal. The DC value from the RMS converter 181 is applied to the HI input terminal of a digital voltmeter 105 which develops at its outputs signals to directly drive variable color digital display 40, to thereby indicate the measured RMS value in digital format, in a manner well known to those having ordinary skill in the art.

[0229] The invention resides in the addition of a crest factor converter 183 for computing the crest factor value of the measured waveform, and of a color converter 55 for controlling the color of display 40 in accordance with the crest factor value. The RMS digital voltmeter of the present invention will simultaneously indicate the RMS value of the measured waveform in digital format and in a color indicative of the crest factor value of the measured waveform, to thereby simultaneously indicate its magnitude and shape.

[0230] FIG. 77 is a comparison chart of RMS and crest factor values for several exemplary waveforms. It is readily apparent that the crest factor value is a good indication of the waveform shape. The unity value of the crest factor indicates that the measured signal is either a symmetrical waveform or a DC signal. Small values of the crest factor (less than 2) usually indicate either a sine wave, triangle wave, or a low duty cycle pulse train. High values of the crest factor (greater than 4) usually indicate a noise signal or a pulse train with a high duty cycle.

[0231] As illustrated in FIG. 78, the crest factor converter 183 includes a ratio producing circuit 187 that develops at its output RATIO A:B a signal representative of the ratio of signals applied to its inputs A and B. The peak signal value, obtained from the output of the peak detector 185, is applied to the input A. The RMS signal value, obtained from the output of the RMS-to-DC converter 181, is applied to the input B. The computed ratio of the peak signal value to the RMS signal value, developed at the output RATIO A:B, is by definition a crest factor value of the measured signal.

[0232] In a simplified exemplary schematic diagram of a ratio producing circuit, shown in FIG. 79, the output DC voltage of the RMS-to-DC converter 181 is applied to the X1 input of a precision divider 188, while the output DC voltage of the peak detector 185 is applied to its input Z2. The precision divider 188 develops at its output suitably scaled DC voltage representing the ratio of the signals Z2 to X1.

[0233] In an exemplary detail of the RMS converter circuit, shown in FIG. 80, the measured signal is applied, via suitable potentiometer 127c, to the input of an RMS-to-DC converter 182, which develops at its output a DC voltage corresponding to RMS value of the measured signal. The potentiometer 127band resistors 124p, 124rare used to adjust offset voltage; the capacitor 129pis selected to set a suitable averaging time constant.

[0234] FIG. 81 is an exemplary detail of the peak detector circuit, in which a measured signal is applied, via a suitable resistor 124u, to the input of a peak detector 186, which develops at its output a DC voltage, retained on the hold capacitor 129r, representing the maximum value of the input signal. The present peak value may be from time to time reset, by applying a relatively short positive pulse 99pto interconnected inputs DET and RESET. When pulse 99preturns to a low logic level, new peak of the input signal may be measured.

[0235] As shown in FIG. 82 in a block diagram form, the output voltage of the crest factor converter, which indicates the instant measured value of the crest factor, may be applied to input of a suitable comparator 141a, such as the one shown in FIG. 23, to develop color control logic signals R, Y, G for the color control circuit 52, to illuminate display element 42 in one of three colors, in accordance with the value of the crest factor. By way of an example, the comparator 141amay be set to develop active color control signal G for values of the crest factor less than 1.5, to illuminate display element 42 in green color, active color control signal Y for values of the crest factor between 1.5 and 2.5, to illuminate display element 42 in yellow color, and active color control signal R for values of the crest factor greater than 2.5, to illuminate display element 42 in red color.

[0236] A similar block diagram shown in FIG. 83 differs in that a comparator 141b, such as the one shown in FIG. 25, and color control circuit 53 are used to illuminate display element 43 in one of seven colors, in accordance with the value of the crest factor. By way of an example, the comparator 141bmay develop active color control signal B for values of the crest factor less than 1.1, to illuminate display element 43 in blue color, active color control signal P for values of the crest factor between 1.1 and 1.4, to illuminate display element 43 in purple color, active color control signal BG for crest factor values between 1.4 and 1.7, to illuminate display element 43 in blue-green color, active color control signal G for crest factor values between 1.7 and 2.0, to illuminate display element 43 in green color, active color control signal Y for crest factor values between 2.0 and 2.5, to illuminate display element 43 in yellow color, active color control signal W for crest factor values between 2.5 and 3.0, to illuminate display element 43 in white color, active color control signal R for crest factor values greater than 3.0, to illuminate display element 43 in red color.

[0237] As shown in FIG. 84, the output voltage of the crest factor converter 183 is applied to the input of a scaling circuit 80a, such as the one shown in FIG. 31, to be scaled and shifted to a voltage range suitable for the continuous 2-primary color converter 57, which will develop drive signals for controlling red bus 5 and green bus 6, respectively, of display 42, to illuminate it in a color related -to the instant measured value of the crest factor.

[0238] A like block diagram shown in FIG. 85 differs in that 3-primary color converter 58 is used to develop drive signals for red bus 5, green bus 6, and blue bus 7, respectively, of display element 43, to illuminate it in a color related to the measured value of the crest factor. The relationship between the crest factor values and the color of display element 43 may be defined at will, e.g., by programming suitable data into PROMs contained in color converter 58, as previously described.

[0239] In FIG. 86 is shown a front view of a digital multimeter which includes a 6½ digit variable color digital display 49, keyboard 117, and suitable terminals 116 for attaching thereto the measuring cords. The keyboard 117 includes a DC V key 118afor setting the multimeter to its DC voltage mode, AC V key 118bfor setting the multimeter to its AC voltage mode, OHMS key 118cfor setting the multimeter to its OHMS mode, RANGE keys 118d, 118e, 118f, 118g, 118h, 118ifor setting the multimeter to a selected range, LOCAL key 118jfor setting the multimeter to its local mode, FRONT key 118kfor selecting front measurement terminals, FILTER key 118mfor setting the multimeter to its filter mode, AUTO key 118nfor setting the multimeter to its autoranging mode, OFFS key 118p, ‘%’ key 118r, and LAH key 118sfor setting the multimeter to certain of its mathematical modes. The HI INPUT terminal 116aand LO INPUT terminal 116bmay be used for voltage measurements; the like HI OHM Terminal 116cand LO OHM terminal 116dmay be used for resistance measurements.

[0240] In FIG. 87 is shown a block diagram of a variable color digital multimeter controlled by a microprocessor or microcomputer 168, which can be influenced either locally, by entering commands via the keyboard 117, or remotely, by sending commands over a bus via the remote control circuit 169. When properly commanded, the microprocessor 168 can control the input conditioning section 120, AC section 112, and OHMS section 113, to selectively switch, scale, attenuate, rectify, and filter the measured signals, before being applied to the input of an A/D converter 106, which repeatedly performs analog-to-digital conversions and develops output data indicative of the magnitude of the instant measured signal. The microprocessor 168 can from time to time read output data of the converter 106 and send same to display controller 167, which causes the data to be indicated on display 40 in digital format. The invention resides in the addition of a color memory 136, wherein data symbolizing a selected color may be stored, and color control 50 for illuminating display 40 in the selected color. It is contemplated that the color of display 40 may be controlled in accordance with certain of the following operating modes:

[0241] a. Local/remote mode: The multimeter may be set either to its local mode, e.g., by actuating the LOCAL key 118jon the front panel, wherein all commands are entered via the keyboard 117, and the remote control 169 is disabled, or to its remote mode wherein all commands are sent via the remote control 169, and the keyboard 117 is disabled. When in its local mode, microprocessor 168 will send data to the color memory 136 commanding color control 50 to illuminate display 40 in a first color (e.g., green); when in its remote mode, microprocessor 168 will send different data to color memory 136 commanding that display 40 be illuminated in a second color (e.g., red), so that an operator may readily distinguish the two modes.

[0242] b. Normal/offset mode: The multimeter may be set to its offset mode, e.g., by actuating the OFFS key 118pon the front panel, wherein a numeric constant (an offset) is stored in the microprocessor's memory, to calculate and display the difference between a measured value and the offset; when in its normal mode, the multimeter displays true measured values. To indicate in which mode the multimeter currently operates, the microprocessor 168 will send data to the color memory 136 commanding that display 40 be illuminated in a first color when in its normal mode and in a second color when in its offset mode.

[0243] c. Standard/percent mode: The multimeter may be set to its percent mode, e.g., by actuating the ‘%’ key 118ron the front panel, wherein a percent deviation of a measured value from a value stored in the microprocessor's memory (reference value) is calculated and displayed; when in its standard mode, true measured values are displayed. To indicate in which mode the multimeter currently operates, microprocessor 168 will send data to color memory 136 commanding that display 40 be illuminated in a first color for the standard mode and in a second color for the percent mode.

[0244] d. LAH/standard mode: The multimeter may be set to its LAH (Low, Average, High) mode, e.g., by actuating the LAH key 118son the front panel, wherein the multimeter will store the most positive and most negative measured values, calculate the average measured value, and count the number of measurements during the LAH cycle; when in its standard mode, true measured values are displayed. To indicate whether the multimeter currently operates in the standard or LAH mode, the microprocessor 168 will send data to the color memory 136 commanding that display 40 be illuminated in a first color for the standard mode and in a second color for the LAH mode.

[0245] In FIG. 88 is shown an expanded block diagram of a digital multimeter with a DC section 111 for processing DC signals, AC section 112 for processing AC signals, and OHMS section 113 for performing resistance measurements, as will be more fully explained later. The multimeter includes input terminals HI INPUT 116a, LO INPUT 116b, HI OHM 116c, LO OHM 116don the front panel shown in FIG. 86, and like input terminals on the rear panel (not shown), which may be selectively connected to the input of a digital voltmeter 105. To select between the front and rear measurements, the FRONT key 118kmay be actuated, which toggles a front/rear relay 191 between its energized and disenergized conditions. To facilitate the illustration, a convention was adopted that a particular relay is designated in the drawings by a certain numeral, and its associated contacts are designated by same numeral with character ‘a’, ‘b’, etc., appended. By way of an example, relay 191 has contacts 191a, 191b, 191c, 191d, 191e. When relay 191 is not energized, its contacts 191ato 191eare in the positions as illustrated, thereby making available the front input terminals for connection to the input of digital voltmeter 105. When relay 191 is energized, its contacts 191ato 191eswitch to their other positions, respectively, thereby making available the rear input terminals for connection to the input of the digital voltmeter 105. The invention resides in the addition of relay contact 191e, associated with contacts 191ato 191d, such that the front and rear measurements are indicated in a digital format and in respectively different colors. When the measurements via the front input terminals are performed, as illustrated, relay contact 191eis open, and the color control input C1 is pulled to a low logic level by a suitable pull-down resistor 124v, thereby forcing, via an inverter 151e, the color control input C2 to rise to a high logic level, to thereby cause display 40 to be illuminated in the color C2 (e.g., red). When the measurements via the rear input terminals are performed, by causing relay 191 to be energized to switch its contacts 191ato 191eto their other positions, respectively, contact 191eis closed to apply a high logic level from the source +VCC to the color control input C1, and to simultaneously force, via inverter 151e, the color control input C2 to a low logic level, to thereby cause display 40 to be illuminated in the color C1 (e.g., green).

[0246] In FIG. 89 is shown a like block diagram of a digital multimeter for selectively performing DC, AC, and OHMS measurements and for indicating measured values in digital format and in respectively different colors. To perform DC measurements, the DC relay 192 is energized, e.g., by actuating the DC V key 118aon the front panel of the, to connect the HI INPUT terminal, via contact 191aand closed contact 192a, and via the DC section 111, to the HI input of digital voltmeter 105. Simultaneously, the LO relay 195 is energized to connect the LO INPUT terminal, via contact 191band closed contact 195a, to the LO input of digital voltmeter 105. Measured DC values of the input signal are indicated on display 40 in digital format, in a manner well understood by those skilled in the art. The invention resides in the provision of a relay contact 192b, associated with contact 192a, to apply a high logic level to the color control input C1, to cause display 40 to illuminate in the color C1 (e.g., red).

[0247] To perform AC measurements, the AC relay 193 is energized, e.g., by actuating the AC V key 118bon the multimeter's front panel, to connect the HI INPUT terminal, via contact 191aand closed contact 193a, and via the AC section 112, to the HI input of digital voltmeter 105. Simultaneously, LO relay 195 is energized to connect the LO INPUT terminal to the LO input of the digital voltmeter 105. Measured AC values of the input signal are indicated on display 40 in digital format, in a manner well understood. The relay contact 193b, associated with contact 193a, closes when relay 193 is energized, to apply a high logic level to the color control input C2, to cause display 40 to illuminate in the color C2 (e.g., yellow).

[0248] To perform OHMS measurements, the OHMS relay 124 is energized, e.g., by actuating the OHMS key 118con the multimeter's front panel, to connect the HI OHM terminal, via closed contact 194a, and via OHMS section 113, to the HI input of digital voltmeter 105. The LO OHM terminal is connected, via closed contact 194b, to the LO input of digital voltmeter 105. Measured resistance values are indicated on display 40 in digital format, in a manner well known. The relay contact 194c, associated with contacts 194a, 194b, closes when relay 194 is energized, to apply a high logic level to the color control input C3, to cause display 40 to illuminate in the color C3 (e.g., green).

[0249] The digital voltmeter shown in FIG. 90 may be set to its filter mode wherein the measured signal is filtered to remove high frequency noise. The invention resides in the addition of a filter flip-flop 138bfor activating color control circuit 50 to illuminate display 40 in the color C1 for the filter mode turned on and in the color C2 for the filter mode turned off. The filter mode may be turned on and off by actuating the FILTER key 118m, to toggle filter flip-flop 138b. When key 118mis actuated, its associated keyswitch 119mmomentarily closes, to connect a low logic level to the trigger input TRG of a timer 158, which is normally tied to a high logic level via its pull-up resistor 124i, to produce at the timer's output OUT a relatively short positive going pulse 99s, to trigger filter flip-flop 138bto its opposite state. The width of pulse 99smay be set by selecting suitable values of resistor 124zand capacitor 129s, to eliminate the problem of possible bouncing of keyswitch 119m. When flip-flop 138bis in its set condition, its output Q, which is connected to the input of a relay driver 157, rises to a high logic level, to activate the latter, to energize filter relay 196. The associated relay contact 196acloses to connect filter circuit 149 to the input of digital voltmeter 105. The outputs Q and {overscore (Q)} of flip-flop 138bare connected to the color control inputs C1, C2, respectively, to cause display 40 to illuminate in a color in accordance with the condition of flip-flop 138b.

[0250] In brief summary, the invention describes a measuring system which comprises two devices for measuring two independent input signals and for developing two sets of data indicative of the respective measured values of the two signals. A single display device is provided which includes a plurality of side by side positioned variable color light emitting diode digital display elements. The first set of the data is exhibited on certain of the display elements. The second set of the data is exhibited on the remaining of the display elements. A color control is further provided for illuminating the first set of the data in a first color, and the second set of data in a second color, in order to distinguish them comfortably.

[0251] It would be obvious, in the view of the present disclosure, that the hardware design of the present invention may be also implemented by software. It would be further 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. It is contemplated that the principles of the invention are also applicable to numerous diverse types of display devices, such as luminescent devices, liquid crystal display devices, plasma display devices, cathode ray tube display devices, and the like.

[0252] The examples of commercially available components should be considered as merely illustrative. It will be appreciated that other components may be readily and effectively used. The integrated circuits used in the description of the invention are manufactured by several well known companies, such are Analog Devices, Inc., Fairchild Camera and Instrument Corporation, Intel Corporation, Intersil, Inc., Motorola Semiconductor Products Inc., National Semiconductor Incorporated, Precision Monolithics Incorporated, Teledyne Semiconductor, Texas Instruments Inc., etc.