# Patent

## Title
Method for the control of ground bounce below an internal ground plane

## Abstract

This is a division of my copending application Ser. No. 07/628,328, filed on Dec. 14, 1990, now U.S. Pat. No. 5,122,733, entitled variable Color Digital Multimeter, 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.

## Background
Reference is also made to my related application 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. 06/839,626, filed on Mar. 14, 1986, entitled Variable Color Display Typewriter, now abandoned, 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. 07/000,478, filed on Jan. 5, 1987, entitled Variable Color Digital Tachometer, now abandoned, Ser. No. 07/113,255, filed on Oct. 27, 1987, entitled Digital Display Timepiece, now U.S. Pat. No. 4,785,432, issued on Nov. 15, 1988, and 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, which describe devices employing a variable color display.

1. Field of the Invention

This invention relates to measuring devices utilizing a variable color digital display.

2. Description of the Prior Art

A display device that can change color and selectively display characters is described in my U.S. Pat. No. 4,086,514, issued on Apr. 25, 1978 and entitled Variable Color Display Device.

Multimeters with monochromatic digital display are well known and extensively used. Such multimeters, however, are capable of indicating value of only one measured quantity at a time. They are not capable of simultaneously indicating values of two different quantities, nor are they capable of indicating the relationship of instantly displayed measured value to values measured at other times, nor are they capable of indicating the relationship of the displayed measured value to measurement limits.

A hand held testing device for measuring different electrical quantities disclosed in U.S. Pat. No. 4,298,837, issued on Nov. 3, 1981 to Manfred Koslar, includes test prongs, function and range selectors, and display mounted within a handle such that they may be viewed together.

A digital ohmmeter with electrical continuity tester disclosed in U.S. Pat. No. 4,228,394, issued on Oct. 14, 1980 to John B. Crosby, includes a digital readout, for displaying the measured value of resistance, on which an Omega symbol may be energized to give a rapid indication of the continuity condition.

In a broad sense, it is the principal object of this invention to provide a measuring instrument with a variable color digital display.

The present invention provides a new dimension in the digital display art. Completely new, unexpected and heretofore impossible, features may be obtained when a well known monochromatic digital display is substituted with a variable color digital display. In the preferred embodiment, the invention was advantageously incorporated into a digital multimeter. However, the invention is not limited to measuring instruments and may be utilized in a wide variety of devices, without imposing any limitations.

It is another object of the invention to provide step variable 2-primary and 3-primary color control circuit which is capable of illuminating the display in a selected one of several possible colors.

It is further object of the invention to provide continuously variable 2-primary and 3-primary color converter for converting an input voltage to variable color which is capable of illuminating the display in any color of the spectrum, in accordance with the magnitude of the input voltage.

Among other objects of the invention are provision of a digital multimeter capable of selectively measuring values of several different measurement quantities and of indicating values of the selected quantity in digital format and in a color unique to the selected measured quantity; provision of a digital multimeter capable of measuring signals by several different measurement methods and of indicating measured values in digital format and in a color depending on the selected measurement method; provision of a digital multimeter capable of making measurements in several different measurement units and of indicating measured values in digital format and in a color depending on the selected measurement unit; provision of a digital multimeter capable of selectively measuring signal values from several different locations and of indicating measured values in digital format and in a color unique to the selected location; provision of a digital multimeter having several different measurement modes and capable of indicating measured values in digital format and in a color unique to the selected measurement mode; provision of a digital multimeter capable of performing several measurement functions and of indicating measured values in digital format and in a color unique to the selected measurement function; provision of a digital multimeter having selectable measurement ranges and capable of indicating measured values in digital format and in a color unique to the selected measurement range; provision of a digital multimeter having several measurement modifiers and capable of indicating measured values in digital format and in a color depending on the selected modifier; provision of a digital multimeter capable of selective measurement control and of indicating measured values in digital format and in a color depending on the selected control; provision of a digital multimeter capable of measuring time and of indicating measured values in digital format and in a color related to time; provision of a digital multimeter having a memory for storing reference values and a comparator for effecting a comparison between the reference values and measured values, and for accordingly causing measured values to be indicated in digital format and in a color depending on the results of the comparison; provision of a digital multimeter capable of performing repeated measurements and of comparing measured values with reference values and of counting the number of measurement errors, and for accordingly causing measured values to be indicated in digital format and in a color having relation to the number of previous measurement errors; provision of a digital multimeter capable of indicating measured values in digital format and in a color different for positive and negative results; provision of a variable color digital display system for emphasizing decimal point in displayed decimal numbers; provision of a variable color digital display system capable of displaying decimal numbers and integers in different colors; provision of a variable color digital barometer with memory, capable of indicating instant atmospheric pressure in digital format and in a color depending on previous measurements; and provision of a dual variable color digital voltmeter capable of simultaneously indicating two different measured values on a single display in different colors.

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

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

FIG. 2 Is a generalized block diagram of a variable color digital display system for the practice of the present invention.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

FIG. 17 s a simplified schematic diagram, similar to FIG. 11, showing how number `7` can be displayed in three different colors.

FIG. 18 is a simplified schematic diagram, similar to FIG. 12, showing how number `1` can be displayed in seven different colors.

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

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

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

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

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

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

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

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

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

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

FIG. 29 is an expanded block diagram of FIG. 27.

FIG. 30 is an expanded block diagram of FIG. 28.

FIG. 31 is a schematic diagram of a scaling circuit.

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

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

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

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

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

FIG. 37 is a continuation of the timing diagram of FIG. 36.

FIG. 38 is a graphic representation of TABLE 1.

FIG. 39 is a graphic representation of TABLE 2.

FIG. 40 is a graph of the ICI chromaticity diagram.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

FIG. 77 is an RMS and crest factor chart.

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

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

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

FIG. 81 is a schematic diagram of a peak detector.

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

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

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

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

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

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

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

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

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

Throughout the drawings, like characters indicate like parts.

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,

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

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

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

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 10a for 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.

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 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.

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 51.

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

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 logic 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.

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 logic 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.

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.

In FIG. 8, red LED 2e and green LED 3e are placed on the base of a segment body 15a which is filled with a transparent light scattering material 16. When forwardly biased, LEDs 2e and 3e emit light signals of red and green colors, respectively, which are scattered within transparent material 16, thereby blending the red and green light signals into a composite light signal that emerges at the upper surface of segment body 15a. The color of the composite light signal may be controlled by varying the portions of the red and green light signals.

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.

In FIG. 10, red LED 2e, green LED 3e, and blue LED 4e are placed on the base of a segment body 15b which 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.

When forwardly biased, LEDs 2e, 3e, and 4e emit 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.

In 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 2i are interconnected to a common electric path referred to as a red bus 5. The cathodes of all green LEDs 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3i are interconnected to a like common electric path referred to as a green bus 6.

The red bus 5 is connected to the output of a tri-state inverting buffer 63a, capable of sinking sufficient current to forwardly bias all red LEDs 2a to 2i in display element 42. The green bus 6 is connected to the output of a like buffer 63b. The two buffers 63a and 63b can 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 and 63b are 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 buffers 63a and 63b are disabled, both red bus 5 and green bus 6 are effectively disconnected to cause display element 42 to be completely extinguished.

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 2g are 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 3g are 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 4g are interconnected to form a like common electric path referred to as a blue bus 7.

The red bus 5 is connected to the output of a noninverting tri-state buffer 62a, capable of sourcing sufficient current to illuminate all red LEDs 2a to 2g in 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 62c can 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 62c are 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 62c are disabled, red bus 5, green bus 6, and blue bus 7 are effectively disconnected to cause display element 43 to be completely extinguished.

In FIG. 13 is shown a logic circuit 69a for 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 69a combines 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.

In FIG. 14 is shown a like logic circuit 69b for 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 69b combines 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.

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 69a employing 2-input logic OR gates 60a and 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 69b employing 4-input logic OR gates 61a, 61b, and 61c similarly 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.

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 0 111 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.

To illuminate display element 42 in red color, the color control input R is raised to a high logic level, and the color control inputs Y and G are maintained at a low logic level. As a result, the output of OR gate 60a rises to a high logic level, thereby causing the output of buffer 63a to drop to a low logic level. The current flows from the output a of decoder driver 23, via red LED 2a and red bus 5, to current sinking output of buffer 63a. Similarly, the current flows from the output b of decoder driver 23, via red LED 2b and red bus 5, to the output of buffer 63a. The current flows from the output c of decoder driver 23, via red LED 2c and red bus 5, to the output of buffer 63a. As a result, segments a, b, and c illuminate in red color, thereby causing a visual impression of a character `7`. The green LEDs 3a, 3b, and 3c remain extinguished because the output of buffer 63b is at a high logic level, thereby disabling green bus 6.

To illuminate display element 42 in green color, the color control input G is raised to a high logic level, while the color control inputs R and Y are maintained at a low logic level. As a result, the output of OR gate 60b rises to a high logic level, thereby causing the output of buffer 63b to drop to a low logic level. The current flows from the output a of decoder driver 23, via green LED 3a and green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder driver 23, via green LED 3b and green bus 6, to the output of buffer 63b. The current flows from the output c of decoder driver 23, via green LED 3c and green bus 6, to the output of buffer 63b. As a result, segments a, b, and c illuminate in green color. The red LEDs 2a, 2b, and 2c  remain extinguished because the output of buffer 63a is at a high logic level, thereby disabling red bus 5.

To illuminate display element 42 in yellow color, the color control input Y is raised to a high logic level, while the color inputs R and G are maintained at a low logic level. As a result, the outputs of both OR gates 60a and 60b rise to a high logic level, thereby causing the outputs of both buffers 63a and 63b to drop to a low logic level. The current flows from the output a of decoder driver 23, via red LED 2a and red bus 5, to current sinking output of buffer 63a, and, via green LED 3a and green bus 6, to current sinking output of buffer 63b. Similarly, the current flows from the output b of decoder driver 23, via red LED 2b and red bus 5, to the output of buffer 63a, and, via green LED 3b and green bus 6, to the output of buffer 63b. The current flows from the output c of decoder driver 23, via red LED 2c and red bus 5, to the output of buffer 63a, and, via green LED 3c and green bus 6, to the output of buffer 63b. As a result of blending light of red and green colors in each segment, segments a, b, and c illuminate in substantially yellow color.

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.

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 61a rises to a high logic level, thereby causing the output of buffer 62a to 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. As a result, segments b and c illuminate in red color, thereby causing a visual impression of a character `1`. The green LEDs 3b, 3c and blue LEDs 4b, 4c remain extinguished because green bus 6 and blue bus 7 are disabled.

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 61b rises to a high logic level, thereby causing the output of buffer 62b to 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. 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 61c rises to a high logic level, thereby causing the output of buffer 62c to 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.

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 61a and 61b rise to a high logic level, thereby causing the outputs of buffers 62a and 62b to 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.

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 61a and 61c rise to a high logic level, thereby causing the outputs of buffers 62a and 62c to 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.

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 61b and 61c rise to a high logic level, thereby causing the outputs of buffers 62b and 62c to 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.

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 61c rise to a high logic level, thereby causing the outputs of buffers 62a, 62b, and 62c to 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.

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).

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 1d arranged in a 7-segment font. The color control inputs R, Y, and G of color controls 52a, 52b, 52c, and 52d of all display elements 46a, 46b, 46c, and 46d are respectively interconnected, 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 46d in a color determined by the instant conditions of the color control inputs R, Y, and G.

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 1d arranged in a 7-segment font. Similarly, the color control inputs B, P, BG, G, Y, W, and R of color controls 53a, 53b, 53c, and 53d of all display elements 47a, 47b, 47c, and 47d are interconnected, and the conditions of respective display elements 47a, 47b, 47c, and 47d are 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 47d in a color determined by the instant conditions of the color control inputs B, P, BG, G, Y, W, and R.

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.

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.

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 85a accepts at its input voltage from an analog 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.

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 85b accepts at its inputs voltage from analog 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.

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

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

When the voltage developed by analog source 11 is between the low voltage limit Vlo and high voltage limit Vhi, the outputs of comparators 82a and 82b rise 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 illuminate display element 42 in green color.

FIG. 24 is a graph depicting the relationship between the input voltage of the comparator circuit shown in FIG. 23 and the color of display element 42 shown in FIG. 11. The display element 42 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.

In FIG. 25, the output voltage of analog 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 92c to 92h. The outputs of comparators 82c to 82h are respectively connected, via inverters 65c to 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 priority encoder 67 are respectively connected, via inverters 65j to 65m, to the inputs A0, A1, and A2 of a 3-to-8 line decoder 68, to decode the outputs of priority encoder 67 into seven mutually exclusive active logic low outputs Y1 to Y7. The outputs Y1 to Y7 are respectively connected, via inverters 65p to 65v, to the color control logic inputs B, P, BG, G, Y, W, R of display element 43.

When the output voltage of analog source 11 is lower than the lowest voltage limit V1, the output of comparator 82c drops 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 65j to 65m to 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.

When the output voltage of analog source 11 is between the adjacent voltage limits, e.g., V4 and V5, the output of comparator 82f rises 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.

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 43 shown in FIG. 12. The display element 42 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.

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.

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.

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 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 electric signals developed by device 10.

The display system shown in FIG. 29 utilizes a scaling circuit 80a which 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 74a are 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 color converter 57 which will develop control signals for red bus 5 and green bus 6, respectively, of variable color display element 42.

The display system shown in FIG. 30 utilizes a scaling circuit 80b and an A/D converter 74b for converting the instant value of an input analog voltage to a digital code. The outputs of A/D converter 74b are 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 76a are applied to red color converter 59a which will develop control signals for red bus 5 of variable color display element 43. The output data of memory 76b are applied to green color converter 59b which will develop control signals for green bus 6 of display element 43. The output data of memory 76c are applied to blue color converter 59c which will develop control signals for blue bus 7 of display element 43.

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 81a and 81b in a standard inverting configuration. The amplifier 81a is set for a unity gain by using resistors 90a and 90b of equal values; potentiometer 92a is adjusted to set a desired offset voltage. The amplifier 81b sets the gain by adjusting feedback potentiometer 92b to 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.

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 90e to 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 99a to 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 respectively connected to 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.

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 99b of 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 71e and 71f to step them down. At the end of each counter cycle, which takes 256 clock cycles to complete, the Terminal Count output TC of counter 71e drops to a low logic level for one clock cycle, to thereby indicate that the lowest count was reached. The negative pulse 99c at 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 99c triggers flip-flop 73 into its set condition wherein its output Q rises to a high logic level.

The counter 71f will 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 Q is at a high logic level for a complementary period of time.

The Q and Q outputs of flip-flop 73 are connected to red bus 5 and green bus 6, respectively, via suitable buffers 63a and 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.

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 99c loads data `FD` into counter 71f. Simultaneously, flip-flop 73 is set by the rising edge of pulse 99c. The counter 71f will 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 99d is 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 99c at 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.

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 71f will count down and will reach zero count after 2 clock cycles. At that instant it produces at its output TC a negative pulse 99e to 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.

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 71f will count down and will reach zero count after 128 clock cycles. At that instant it produces at its output TC a negative pulse 99f to 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.

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 99b is applied to the CP inputs of counters 71d, 71a, 71b, and 71c to step them down. Every 256 counts a negative pulse 99c is generated at the TC output of counter 71d, to load data into counters 71a, 71b, and 71c from respective memories 76a, 76b, and 76c, and to set flip-flops 73a, 73b, and 73c. The data in red memory 76a represent the portions of red color, the data in green memory 76b represent the portions of green color, and the data in blue memory 76c represent the portions of blue color to be blended.

The counters 71a, 71b, and 71c will 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 71c reaches zero count, its TC output momentarily drops to a low logic level, to reset its associated flip-flop (red counter 71a resets its red flip-flop 73a, green counter 71b resets its associated green flip-flop 73b, and blue counter 71c resets its associated blue flip-flop 73c). Eventually, all three flip-flops 73a, 73b, and 73c will be reset. The Q outputs of flip-flops 73a, 73b, and 73c are connected to red bus 5, green bus 6, and blue bus 7, respectively, via suitable buffers 62a, 62b, and 62c, shown in FIG. 12, to respectively energize red bus 5, green bus 6, and blue bus 7 for variable periods of time.

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 99c simultaneously loads data `80` from red memory 76a into red counter 71a, data `00` from green memory 76b into green counter 71b, and data `80` from blue memory 76c into blue counter 71c. The counters 71a, 71b, and 71c will be thereafter stepped down. The red counter 71a will reach its zero count after 128 clock cycles; green counter 71b will reach its zero count immediately; blue counter 71c will reach its zero count after 128 clock cycles.

It is readily apparent that red flip-flop 73a was set for 128 clock cycles, or about 50% of the time, green flip-flop 73b was never set, and blue flip-flop 73c was 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.

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 71a will reach its zero count immediately, green counter 71b will reach its zero count after 128 clock periods, and so will blue counter 71c.

The red flip-flop 73a was never set, green flip-flop 73b was 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.

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 71a will reach its zero count after 64 clock cycles, and so will green counter 71b. The blue counter 71c will reach its zero count after 128 clock cycles.

The red flip-flop 73a was set for 64 clock cycles, or about 25% of the time, and so was green flip-flop 73b. The blue flip-flop 73c was 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.

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` are loaded into blue counter 71c. The red counter 71a will reach its zero count after 128 clock cycles, green counter 71b will reach its zero count after 64 clock cycles, and so will blue counter 71c.

The red flip-flop 73a was set for 128 clock cycles, or about 50% of the time, green flip-flop 73b and blue flip-flop 73c were 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.

By referring now more particularly to FIGS. 38 and 39, which are graphic representations of TABLES 1 and 21 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.

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.

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.

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).

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.

In the examples of the characteristics of color converters shown in TABLE 1 and TABLE 21 the data values stored in red memory 76a, green memory 76b, and blue memory 76c are 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 76c may 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.

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.

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 55 for converting values of a QUANTITY 2 to color control signals and for accordingly controlling the color of display 40. The display 40 thus simultaneously indicates values of QUANTITY 1, in digital format, and values of QUANTITY 2, in variable color.

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 of FIG. 41 in that multimeter with multiplexed outputs 102 develops multiplexed signals to directly drive multiplexed variable color digital display 41.

A digital multimeter shown in a block diagram configuration in FIG. 43 is capable of selectively setting certain of its external controls 115a, 115b, 115c to 115n by an external control selector 121a. The invention resides in the addition of associated color selector 121b for causing variable color digital display 40 to illuminate in a color corresponding to the selected external control 115a, 115b, 115c, or 115n. The measurements performed with different external controls are displayed in respectively different colors. The selectors 121a and 121b may include relays, mechanical switches, electronic and optical elements, devices for executing program of instructions, and the like. The association between selectors 121a and 121b may be, in its simplest form, a direct coupling, whereby selector 121b is always in the same position as selector 121a, or a more sophisticated association in space, time, hardware, and software. The external controls 115a, 115b, 115c to 115n 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.

In FIG. 44 is shown a block diagram of a like digital multimeter- capable of selectively setting certain of its internal measurement controls, referred to as CONTROL 1, CONTROL 21 CONTROL 3 to CONTROL N, by an internal control selector 121a. The associated color selector 121b causes display 40 to illuminate in a color corresponding to the selected internal control, such that the measurements performed with different internal controls are 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.

FIG. 45 is a block diagram of a digital multimeter with measurement quantity selection. The operation of the multimeter may be explained by the example of setting quantity selector 121a to its second position, thereby selecting QUANTITY 2 to the input of digital multimeter 103. The associated color selector 121b is also in its second position, thereby applying the control voltage to the input C2 of color control 50, to cause the measured values of QUANTITY 2 to be indicated on display 40 in the color C2. The measurements of different quantities are indicated in respectively different colors.

FIG. 46 is a block diagram of a digital multimeter with input location selection. The operation of the multimeter may be explained by the example of setting location selector 121a to its third position, thereby selecting for the input of multimeter 103 signals from LOCATION 3. The associated color selector 121b is also in its third position, thereby applying the control voltage to the input C3 of color control 50, to cause the measured values from LOCATION 3 to be indicated on display 40 in the color C3. The measurements from different locations are indicated in respectively different colors.

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 123g is 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 123h is also in its first position, thereby connecting the control voltage +VCC to the input C1 of color control 52, to cause the display 48 to illuminate in the color C1. When switch 123g is 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 123g is 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.

In FIG. 48 is shown an exemplary simplified schematic diagram of a digital multimeter capable of measuring signals from seven different locations, designated as LOCATION 1 to LOCATION 71 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 and 147b, respectively, to cause analog multiplexer 147a to internally route signals from its selected input, e.g., Y1, to its output Y, and, simultaneously, to apply the control voltage +VCC from the terminal Y of analog multiplexer 147b, via its selected terminal, e.g., Y1, to one of the inputs B, P, BG, G, Y, W, or R of color control 53. 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 analog multiplexer 147b with the inputs B to R of color control 53.

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 123i selects either the output of RMS converter 181 or the output of the precision rectifier circuit, consisting of an op amp 159a, resistors 124x, 124y, 124z and diodes 128a, 128b, to the input of digital voltmeter 108. An associated switch 123j selects one of the inputs C1 or C2 of color control 52, 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.

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 and 179, via a switch 123m, to the input of digital voltmeter 108. An associated switch 123n applies the control voltage +VCC to one of the inputs C1, C2, and C3 of color control 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.

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, and 126e, connected in series, convert measured current to voltage, which is applied via resistor 125f to the input terminal IN HI 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 switch 123a such that both switches are always in the same position, to connect the reference voltage +VCC to the selected input C1, C2, C3, C4, or C5 of color control 50, which are tied to ground via suitable pull down resistors 125a, 125b, 125c, 125d, and 125e, in accordance with the selected current range. By way of an example, display 40 may indicate measured current values on 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.

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, and 126j are 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 switch 123c, to apply the reference voltage +VCC to the selected input C1, C2, C3, C4, or C5 of color control 50. By way of an example, display 40 may indicate measured values on 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.

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, and 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 switch 123e, to connect the reference voltage +VCC to the selected input C1, C2, C3, C4, or C5 of color control 50, in accordance with the selected resistance range. By way of an example, display 40 may indicate measured resistance values on 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 1M range in red color.

The examples of range and precision resistor values shown in FIGS. 51, 52, and 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.

In FIG. 54 is shown a detail of the multimeter of FIGS. 51, 52, and 53 which includes a DVM chip 108 capable of converting an analog voltage applied, via resistor 125y and capacitor 129h, to its inputs HI and LO to signals for directly driving respective segments of a 31/2 digit 7-segment variable color display 48. The color control 50 causes display 48 to illuminate in a selected color, as described previously.

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 31/2 digit 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 input R, and, via inverter 151a, to the input G of color control 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 inverter 151a to rise to a high logic level, to activate the input G for causing display 48 to illuminate 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 input R for causing display 48 to illuminate in red color. It would be obvious, in the view of the present disclosure, to devise other color combinations.

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 46a to 46h, of which only displays 46a, 46b, and 46h are shown, is capable of detecting the position of a decimal point in a string of 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-cathode 7-segment decoders 23a, 23b to 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 162d driven by clock 199j of a suitable frequency. When an active high DP output is detected on certain of decoders 23a, 23b to 23h, the inverting output W of multiplexer 146, which is connected to the Set Direct input SD of DP flip-flop 138j, drops to a low logic level 199n, to force the latter to its set condition. The Q output of DP flip-flop 138j, which is connected to the D inputs of all flip-flops 138b to 138h, rises to a high logic level for the remaining time of the scanning cycle, to thereby indicate, as may be best observed in FIG. 57 in the line designated F--F 138j Q OUTPUT at waveform 199p, the position of the detected decimal point in reference to the scanning cycle. The decoder 166 is incremented synchronously with multiplexer 146, and, as a result, its outputs Y0 to Y7 are sequentially driven to a low logic level, to trigger in a sequence flip-flops 138b to 138h to states determined by the conditions of their D inputs, respectively, at the time of triggering, as may be best observed in FIG. 57 in the lines designated DEC 166 OUTPUTS Y0 to Y7 at waveforms 199a to 199h. All flip-flops 138b to 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 138b to 138h, which were triggered after the decimal point was located, are triggered to their set states. The Y7 output of decoder 166 is connected to the Clear Direct input CD of DP flip-flop 138j, to force the latter to its reset condition at the end of each scanning cycle. The outputs Q and Q of flip-flops 138b to 138h are respectively connected to color control inputs R and G of color controls 52b to 52h, to thereby cause all display digits 46b to 46h that precede the instant decimal point to be illuminated in green color, and all remaining display digits 46b to 46h that follow the decimal point to be illuminated in red color. It would be obvious that other color combinations may be devised.

The display system shown in FIG. 58 is capable of detecting the presence or absence of a 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 23a, 23b to 23g, 23h are respectively connected to the inputs of an OR gate 154. When a 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 controls 52a, 52b to 52g, 52h, to rise to a high logic level, to thereby cause all displays 46a, 46b to 46g, 46h to 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 controls 52a, 52b to 52g, 52h, rises to a high logic level, to thereby cause all displays 46a, 46b to 46g, 46h to illuminate in green color.

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

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, 159d and resistors 124a, 124b, 124c, 124d, 124e shifts 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 124e and 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 color control 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 decades 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 165b has 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 99m at the selected output Yn of decoder 165b, 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 inputs R, Y, and G of color control 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 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.

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 clock 148 are decoded by a suitable time decoder 168 and converted to color control signals C1, C2 and C3. Values measured by multimeter 103 are indicated on display 40 in digital format and in a color having relation to time.

FIG. 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, or mechanical storage elements, such are binary switches and the like. When the instant measured value is less than the reference value, the output `<` of comparator 141 is active, thereby activating the input C2 of color control 50 for causing display 40 to illuminate in the color C2. When the instant measured value is greater than the reference one, the output `>` of comparator 141 is active, and the measured value is displayed on display 40 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.

FIG. 63 is a block diagram of a multimeter which includes a memory 131a for storing a low measurement limit, memory 131b for 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 Comparator 141a is active, thereby activating the input C3 of color control 50 for causing display 40 to illuminate in the color C3. When the measurement value is higher that the high measurement limit, stored in memory 131b, the output `>` of comparator 141b is active, thereby activating the input C1 of color control 50 for causing display 40 to illuminate 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 comparator 141a and `<` of comparator 141b are combined in a logic fashion by a logic circuit 150, thereby activating the input C2 of color control 50 for causing display 40 to illuminate in the color C2.

FIG. 64 is a block diagram of a multimeter for making repeated measurements, which includes an A/D converter 106 and combined memory and comparator circuit 144. The instant measured value of an input signal, converted to digital format by A/D converter 106, may be from time to time stored in memory and comparator 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 memory and comparator 144. When the instant measured value is less than that stored in memory and comparator 144, its output LT (Less Than) is active, thereby activating the input C3 of color control 50 for causing display 40 to exhibit the measured value in the color C3. When the instant measured value is equal to that stored in memory and comparator 144, its output EQ (Equal) is active, thereby activating the input C2 of color control 50 for causing display 40 to exhibit the measured value in the color C2. When the instant measured value is greater than that stored in memory and comparator 144, its output GT (Greater Than) is active, thereby activating the input C1 of color control 50 for causing display 40 to exhibit the measured value in the color C1.

FIG. 65 is a block diagram of a multimeter for making a series of measurements and for comparing each measured value, by comparators 141a and 141b, with low and high measurement limits stored in memories 131a and 131b, respectively. An additional error memory 131c, which may include an error counter, and logic circuit 150a are 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 error memory 131c. The decisions may be as simple as merely display 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.

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, representing a 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 32b, representing a 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 comparators 143a and 143b, interconnected in parallel. The comparators 143a and 143b effect 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 comparator 143a rises to a high logic level to generate active signal FAIL LOW LIMIT. When the instant measurement data are greater than the high measurement limit, the `>` output of comparator 143b rises to a high logic level to generate active signal FAIL HIGH LIMIT. When the instant measurement data are between the low and high measurement limits, one of the inputs of each OR gate 152a, 152b rises to a high logic level, thereby forcing both inputs of AND gate 155a to rise to a high logic level, which in turn causes its output to rise to a high logic level to generate active signal PASS. The outputs PASS, FAIL LOW LIMIT, and FAIL HIGH LIMIT may be connected to respective inputs C1, C2, and C3 of 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.

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 132c contains data representing low measurement limits for each measurement step. A like memory 132d contains data representing 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 and 132d. When addressed for a particular measurement step, memories 132c and 132d present the data residing at such address to the inputs B0 to B7 of comparators 143c and 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 and 143d at 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 152e rises to a high logic level, and error memory 135a is incremented by the next clock pulse. Thus error memory 135a contains data representing the total number of measurement errors. A logic circuit 150b converts the instant data of error memory 135a 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.

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 OR gate 152f, which is connected to the D input of error flip-flop 138a, rises to a high logic level, and error flip-flip 138a will be set by the next clock pulse, to indicate that there was a measurement error. The error flip-flop 138a 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 error flip-flop 138a. 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.

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 OR gate 152g, which is connected to the DATA input of error memory 135b, rises to a high logic level, and the contents of error memory 135b will be incremented by the next clock pulse. The error memory 135b thus contains data indicating the total number of previous measurement errors. The outputs of error memory 135b are applied to interconnected inputs of red color converter 59a, green color converter 59b, and blue color converter 59c, which develop drive signals for emergizing red bus 5, green bus 61 and blue bus 7 of display 40 to illuminate it in a color related to the total number of previous measurement errors.

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 and 142b are cascaded to form an 8-bit digital comparator, in a manner well understood by those skilled in the art.

FIG. 71 is an exemplary detail of the error counter and PROM combination of 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 51 green bus 6, and blue bus 7, as previously shown in FIG. 35, to illuminate display 40 in a color depending on the total number of previous measurement errors.

The schematic diagram shown in FIG. 72 includes a digital multimeter 103, for making repeated measurements of input signals applied ti its input IN 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 and 145b, for comparing the instant measured value with the value previously stored. From time to time, a short positive pulse 99n may be applied to interconnected Load inputs S0 and S1, to cause the instant data at the inputs I0 to I7 of both registered comparators 145a and 145b to be loaded therein. The subsequent measured values will be compared with the reference value currently stored in registered comparators 145a and 145b, 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, and 124h, will indicate the result of each comparison. The comparator outputs LT, EQ, and GT are respectively connected to the inputs C1, C2, and C3 of color control 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 registered comparators 145a an 145b. 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.

In FIG. 73 is shown a simplified schematic diagram of a digital voltmeter with 31/2 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 HI via resistor 124a and decoupling capacitor 129m, to 31/2 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, and 22d, to signals for directly energizing the segments of variable color display digits 42a, 42b, 42c, and 42d, respectively, in a manner well understood by those skilled in the art. The color control 50 causes all four display digits 42a, 42b, 42c, and 42d to illuminate uniformly in a selected color.

A like block diagram shown in FIG. 74 differs in that four color controls 50a, 50b, 50c, and 50d are employed to independently control the colors of display digits 42a, 42b, 42c, and 42d.

In FIG. 75 is shown, in a block diagram configuration, a multimeter utilizing two digital voltmeters 109a and 109b for respectively measuring INPUT SIGNAL 1 and INPUT SIGNAL 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, color control 52a has its 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 52b has its input R connected to a high logic level, to illuminate the four least significant digits D5 to D8 in red color.

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.

The digital voltmeter includes an RMS-to-DC 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 RMS converter 181 is applied to the HI input terminal of 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.

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.

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.

As illustrated in FIG. 78, the crest factor converter 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 peak detector 185, is applied to the input A. The RMS signal value, obtained from the output of 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.

In a simplified exemplary schematic diagram of a ratio producing circuit, shown in FIG. 79, the output DC voltage of RMS-to-DC converter 181 is applied to the Xl input of a precision divider 188, while the output DC voltage of 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.

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

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 +IN of peak detector 186, which develops at its output a DC voltage, retained on a 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 99p to interconnected inputs DET and RESET. When pulse 99p returns to a low logic level, new peak of the input signal may be measured.

As shown in FIG. 82 in a block diagram form, the output voltage of crest factor converter 183, which indicates the instant measured value of the crest factor, may be applied to the input of a suitable comparator 141a, such as the one shown in FIG. 23, to develop color control logic signals R, Y, and G for color control 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 141a may be set to develop active color control signal G for values of the crest factor less than 1.51 to illuminate display element 42 in green color, active color control signal Y for values of the crest factor between 1.5 and 2.51 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.

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 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, comparator 141b may 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 2.51 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, and active color control signal R for crest factor values greater than 3.01 to illuminate display element 43 in red color.

As shown in FIG. 84, the output voltage of 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 2-LED continuous color converter 57, which will develop drive signals for controlling red bus 5 and green bus 6, respectively, of display element 42, to illuminate it in a color related to the instant measured value of the crest factor.

A like block diagram shown in FIG. 85 differs in that 3-LED continuous color converter 58 is used to develop drive signals for red bus 51 green bus 61 and blue bus 71 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 continuous color converter 58, as previously described.

In FIG. 86 is shown a front view of a digital multimeter which includes a 61/2 digit variable color digital display 49, keyboard 117, and suitable terminals 116a to 116d for attaching thereto measuring cords. The keyboard 117 includes a DC V key 118a for setting the multimeter to its DC voltage mode, AC V key 118b for setting the multimeter to its AC voltage mode, OHMS key 118c for setting the multimeter to its OHMS mode, RANGE keys 118d, 118e, 118f, 118g, 118h, and 118i for setting the multimeter to a selected range, LOCAL key 118j for setting the multimeter to its local mode, FRONT key 118k for selecting front measurement terminals, FILTER key 118m for setting the multimeter to its filter mode, AUTO key 118n for setting the multimeter to its autoranging mode, OFFS key 118p, `%` key 118r, and LAH key 118s for setting the multimeter to certain of its mathematical modes. The HI INPUT terminal 116a and LO INPUT terminal 116b may be used for voltage measurements; like HI OHM terminal 116c and LO OHM terminal 116d may be used for resistance measurements.

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 remote control 169. When properly commanded, microprocessor 168 can control the input conditioning section 120, AC section 112, and OHMS section 113, to selectively switch, scale, attenuate, rectify, and filter 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 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:

a. Local/remote mode: The multimeter may be set either to its local mode, e.g., by actuating LOCAL key 118j on the front panel, wherein all commands are entered via keyboard 117, and remote control 169 is disabled, or to its remote mode wherein all commands are sent via remote control 169, and keyboard 117 is disabled. When in its local mode, microprocessor 168 will send data to 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.

b. Normal/offset mode: The multimeter may be set to its offset mode, e.g., by actuating OFFS key 118p on the front panel, wherein a numeric constant (an offset) is stored in internal memory of microprocessor 168, 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, microprocessor 168 will send data to 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.

c. Standard/percent mode: The multimeter may be set to its percent mode, e.g., by actuating the `%` key 118r on the front panel, wherein a percent deviation of a measured value from a value stored in the internal memory of microprocessor 168 (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.

d. LAH/standard mode: The multimeter may be set to its LAH (Low, Average, High) mode, e.g., by actuating the LAH key 118s on 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, 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 LAH mode.

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 116d on 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 digital voltmeter 105. To select between the front and rear measurements, FRONT key 118k may 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, and 191e. When relay 191 is not energized, its contacts 191a to 191e are 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 191a to 191e switch to their other positions, respectively, thereby making available the rear input terminals for connection to the input of digital voltmeter 105. The invention resides in the addition of relay contact 191e, associated with contacts 191a to 191d, such that the front and rear measurements are indicated in digital format and in respectively different colors. When the measurements via the front input terminals are performed, as illustrated, relay contact 191e is open, and the input C1 of color control 50 is pulled to a low logic level by a suitable pull-down resistor 124v, thereby forcing, via an inverter 151e, the input C2 of color control 50 to rise to a high logic level, to 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 191a to 191e to their other positions, respectively, contact 191e is closed to apply a high logic level from the source +VCC to the input C1 of color control 50, and to simultaneously force, via inverter 151e, the input C2 of color control 50 to a low logic level, to cause display 40 to be illuminated in the color C1 (e.g., green).

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, DC relay 192 is energized, e.g., by actuating DC V key 118a on the front panel of the multimeter, to connect the HI INPUT terminal, via contact 191a and closed contact 192a, and via DC section 111, to the HI input of digital voltmeter 105. Simultaneously, LO relay 195 is energized to connect the LO INPUT terminal, via contact 191b and 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 input C1 of color control 50, to cause display 40 to illuminate in the color C1 (e.g., red).

To perform AC measurements, AC relay 193 is energized, e.g., by actuating AC V key 118b on the front panel of the multimeter, to connect the HI INPUT terminal, via contact 191a and closed contact 193a, and via 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 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 input C2 of color control 50, to cause display 40 to illuminate in the color C2 (e.g., yellow).

To perform OHMS measurements, the OHMS relay 124 is energized, e.g., by actuating OHMS key 118c on the front panel of the multimeter, 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 and 194b, closes when relay 194 is energized, to apply a high logic level to the input C3 of color control 50, to cause display 40 to illuminate in the color C3 (e.g., green).

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 138b for activating color control 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 FILTER key 118m, to toggle filter flip-flop 138b. When FILTER key 118m is actuated, its associated keyswitch 119m momentarily 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 138b to its opposite state. The width of pulse 99s may be set by selecting suitable values of resistor 124z and capacitor 129s, to eliminate the problem of possible bouncing of keyswitch 119m. When flip-flop 138b is 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 for energizing filter relay 196. The associated relay contact 196a closes to connect filter circuit 149 to the input of digital voltmeter 105. The outputs Q and Q of flip-flop 138b are respectively connected to the inputs C1 and C2 of color control 50 to cause display 40 to illuminate in a color in accordance with the condition of flip-flop 138b.

In brief summary, the invention describes a method and a device for simultaneously displaying values of two different measured quantities on a single variable color digital display device, by causing the value of the first quantity to be indicated in a digital format, and by controlling the color of the display in accordance with the value of the second quantity.

A digital multimeter with variable color digital display was disclosed which can indicate values of the measured quantities in digital format and in a color selectively variable in accordance with the measurement quantity, method, units, mode, function, range, location, modifier, control, measurement limits, and the like.

It would be obvious that numerous modifications can be made in the construction of the preferred embodiments shown herein, without departing from the spirit of the invention as defined in the appended claims. It is contemplated that the principles of the invention may be also applied to numerous diverse types of display devices, such are liquid crystal, plasma devices, and the like.

This is a correlation table of reference characters used in the drawings herein, their descriptions, and examples of commercially available parts. #    DESCRIPTION            EXAMPLE ______________________________________ 1    display segment 2    red LED 3    green LED 4    blue LED 5    red bus 6    green bus 7    blue bus 10   device developing electric signals 11   analog voltage source 12   digital device 15   segment body 16   light scattering material 20   decoder 21   digital decoder driver 22   7-segment display decoder driver 23   common cathode 7-segment decoder 74LS49 driver 24   common anode 7-segment decoder 74LS47 driver 30   monochromatic digital display 40   variable color digital display 41   multiplexed variable color display 42   variable color 7-segment display element (2 LEDs) 43   variable color 7-segment display element (3 LEDs) 46   variable color display element (2 LEDs) 47   variable color display element (3 LEDs) 48   31/2 digit variable color display 49   61/2 digit variable color 7-segment display 50   color control 51   step variable color control 52   color control (2 LEDs) 53   color control (3 LEDs) 55   color converter 56   continuously variable color converter 57   2-primary color converter 58   3-primary color converter 59   single color converter 60   2-input OR gate        74HC32 61   4-input OR gate        4072 62   non-inverting buffer   74LS244 63   inverting buffer       74LS240 64   inverter               part of 74LS240,4 65   inverter               74HC04 66   2-input AND gate       74HC08 67   priority encoder       74HC147 68   3-to-8 line decoder    74HC138 69   logic circuit 71   8-bit counter          74F579 73   D type flip-flop       74HC74 74   A/D converter 75   8-bit A/D converter    AD570 76   memory 77   2k .times. 8 bit PROM  2716 80   scaling circuit 81   op amp                 LM741 82   analog comparator      LM339 85   signal converter 90   resistor 91   resistor 92   potentiometer 93   capacitor 99   pulse 101  multimeter 102  multimeter with multiplexed outputs 103  digital multimeter 105  digital voltmeter 106  A/D converter 107  Teledyne DVM chip      TSC8750 108  Teledyne DVM chip      TSC7107 109  Intersil DVM chip      ILS7107 111  DC section 112  AC section 113  OHMS section 115  control section 116  measuring terminal 117  keyboard 118  key 119  keyswitch 120  input conditioning 121  selector 123  rotary switch 124  resistor 125  resistor 126  precision resistor 127  potentiometer 128  signal diode           1N4148 129  capacitor 131  memory 132  8-bit wide memory 134  8-bit latch            74HC273 135  error memory 136  color memory 138  D-type flip-flop       74HC74 141  comparator 142  4-bit digital comparator 74HC85 143  8-bit digital comparator 144  memory & comparator 145  registered comparator  74F524 146  8-channel digital multiplexer 74HC151 147  analog multiplexer     4051 148  clock 149  filter 150  logic circuit 151  inverter               74HC04 152  2-input OR gate        74HC32 154  8-input OR/NOR gate    74HC4078 155  2-input AND gate       74HC08 156  3-input AND gate       74HC1l 157  relay driver           1416 158  timer                  NE555 159  op amp                 LM741 161  counter 162  4-bit binary counter   74HC161 163  8-bit binary counter   74F579 164  3-decade counter       14553 165  decoder 166  1-to-8 lines decoder   74HC138 167  display controller     ICM7218A 168  microprocessor         8085 169  remote control 172  temperature transducer 173  pressure transducer 174  physiological transducer 176  SenSym pressure transducer LX1802AN 177  Kelvin temperature transducer 178  Celsius temperature transducer LM35 179  Fahrenheit temperature transducer LM34 181  RMS to DC converter 182  RMS converter chip     AD536A 183  crest factor converter 185  peak detector 186  peak detector chip     PKD-01 187  ratio producing circuit 188  precision divider chip AD535 191  front/rear relay       JDT21 192  DC section relay       JDT7 193  AC section relay       JDT7 194  OHMS section relay     JDT15 195  LO input relay         JWD-107 196  filter relay           JWD-107 199  pulse ______________________________________

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. ______________________________________ DATA Input      PROM     `Red` Voltage    Address  PROM       PORTIONS (Volts)    (Hex)    (Hex)      red  green ______________________________________ 0.0        00       00         0.0  1.0 0.039      01       00         0.0  1.0 0.078      02       00         0.0  1.0 0.117      03       00         0.0  1.0 0.156      04       00         0.0  1.0 0.195      05       00         0.0  1.0 0.234      06       00         0.0  1.0 0.273      07       00         0.0  1.0 0.312      08       00         0.0  1.0 0.352      09       00         0.0  1.0 0.391      0A       00         0.0  1.0 0.430      0B       00         0.0  1.0 0.469      0C       00         0.0  1.0 0.508      0D       00         0.0  1.0 0.547      0E       00         0.0  1.0 0.586      0F       00         0.0  1.0 0.625      10       40         0.25 0.75 0.664      11       40         0.25 0.75 0.703      12       40         0.25 0.75 0.742      13       40         0.25 0.75 0.781      14       40         0.25 0.75 0.820      15       40         0.25 0.75 0.859      16       40         0.25 0.75 0.898      17       40         0.25 0.75 0.937      18       40         0.25 0.75 0.977      19       40         0.25 0.75 1.016      1A       40         0.25 0.75 1.055      1B       40         0.25 0.75 1.094      1C       40         0.25 0.75 1.133      1D       40         0.25 0.75 1.172      1E       40         0.25 0.75 1.211      1F       40         0.25 0.75 1.250      20       80         0.5  0.5 1.289      21       80         0.5  0.5 1.328      22       80         0.5  0.5 1.367      23       80         0.5  0.5 1.406      24       80         0.5  0.5 1.445      25       80         0.5  0.5 1.484      26       80         0.5  0.5 1.523      27       80         0.5  0.5 1.562      28       80         0.5  0.5 1.602      29       80         0.5  0.5 1.641      2A       80         0.5  0.5 1.680      2B       80         0.5  0.5 1.719      2C       80         0.5  0.5 1.758      2D       80         0.5  0.5 1.797      2E       80         0.5  0.5 1.836      2F       80         0.5  0.5 1.875      30       C0         0.75 0.25 1.914      31       C0         0.75 0.25 1.953      32       C0         0.75 0.25 1.992      33       C0         0.75 0.25 2.031      34       C0         0.75 0.25 2.070      35       C0         0.75 0.25 2.109      36       C0         0.75 0.25 2.148      37       C0         0.75 0.25 2.187      38       C0         0.75 0.25 2.227      39       C0         0.75 0.25 2.266      3A       C0         0.75 0.25 2.305      3B       C0         0.75 0.25 2.344      3C       C0         0.75 0.25 2.389      3D       C0         0.75 0.25 2.422      3E       C0         0.75 0.25 2.461      3F       C0         0.75 0.25 2.500      40       FF         1.0  0.0 2.539      41       FF         1.0  0.0 2.578      42       FF         1.0  0.0 2.617      43       FF         1.0  0.0 2.656      44       FF         1.0  0.0 2.695      45       FF         1.0  0.0 2.734      46       FF         1.0  0.0 2.773      47       FF         1.0  0.0 2.812      48       FF         1.0  0.0 2.852      49       FF         1.0  0.0 2.891      4A       FF         1.0  0.0 2.930      4B       FF         1.0  0.0 2.969      4C       FF         1.0  0.0 3.008      4D       FF         1.0  0.0 3.047      4E       FF         1.0  0.0 3.086      4F       FF         1.0  0.0 3.125      50       00         0.0  1.0 3.164      51       00         0.0  1.0 3.203      52       00         0.0  1.0 3.242      53       00         0.0  1.0 3.281      54       00         0.0  1.0 3.320      55       00         0.0  1.0 3.359      56       00         0.0  1.0 3.398      57       00         0.0  1.0 3.437      58       00         0.0  1.0 3.477      59       00         0.0  1.0 3.516      5A       00         0.0  1.0 3.555      5B       00         0.0  1.0 3.594      5C       00         0.0  1.0 3.633      5D       00         0.0  1.0 3.672      5E       00         0.0  1.0 3.711      5F       00         0.0  1.0 3.750      60       40         0.25 0.75 3.789      61       40         0.25 0.75 3.828      62       40         0.25 0.75 3.867      63       40         0.25 0.75 3.906      64       40         0.25 0.75 3.945      65       40         0.25 0.75 3.984      66       40         0.25 0.75 4.023      67       40         0.25 0.75 4.062      68       40         0.25 0.75 4.102      69       40         0.25 0.75 4.141      6A       40         0.25 0.75 4.178      6B       40         0.25 0.75 4.219      6C       40         0.25 0.75 4.258      6D       40         0.25 0.75 4.299      6E       40         0.25 0.75 4.336      6F       40         0.25 0.75 4.375      70       80         0.5  0.5 4.414      71       80         0.5  0.5 4.453      72       80         0.5  0.5 4.492      73       80         0.5  0.5 4.531      74       80         0.5  0.5 4.570      75       80         0.5  0.5 4.609      76       80         0.5  0.5 4.648      77       80         0.5  0.5 4.687      78       80         0.5  0.5 4.727      79       80         0.5  0.5 4.766      7A       80         0.5  0.5 4.805      7B       80         0.5  0.5 4.844      7C       80         0.5  0.5 4.883      7D       80         0.5  0.5 4.922      7E       80         0.5  0.5 4.961      7F       80         0.5  0.5 5.000      80       C0         0.75 0.25 5.039      81       C0         0.75 0.25 5.078      82       C0         0.75 0.25 5.117      83       C0         0.75 0.25 5.156      84       C0         0.75 0.25 5.195      85       C0         0.75 0.25 5.234      86       C0         0.75 0.25 5.273      87       C0         0.75 0.25 5.312      88       C0         0.75 0.25 5.352      89       C0         0.75 0.25 5.391      8A       C0         0.75 0.25 5.430      8B       C0         0.75 0.25 5.469      8C       C0         0.75 0.25 5.508      8D       C0         0.75 0.25 5.547      8E       C0         0.75 0.25 5.586      8F       C0         0.75 0.25 5.625      90       FF         1.0  0.0 5.664      91       FF         1.0  0.0 5.703      92       FF         1.0  0.0 5.742      93       FF         1.0  0.0 5.781      94       FF         1.0  0.0 5.820      95       FF         1.0  0.0 5.859      96       FF         1.0  0.0 5.898      97       FF         1.0  0.0 5.937      98       FF         1.0  0.0 5.977      99       FF         1.0  0.0 6.016      9A       FF         1.0  0.0 6.055      9B       FF         1.0  0.0 6.094      9C       FF         1.0  0.0 6.133      9D       FF         1.0  0.0 6.172      9E       FF         1.0  0.0 6.211      9F       FF         1.0  0.0 6.250      A0       00         0.0  1.0 6.289      A1       00         0.0  1.0 6.328      A2       00         0.0  1.0 6.367      A3       00         0.0  1.0 6.406      A4       00         0.0  1.0 6.445      A5       00         0.0  1.0 6.484      A6       00         0.0  1.0 6.524      A7       00         0.0  1.0 6.562      A8       00         0.0  1.0 6.602      A9       00         0.0  1.0 6.641      AA       00         0.0  1.0 6.680      AB       00         0.0  1.0 6.719      AC       00         0.0  1.0 6.758      AD       00         0.0  1.0 6.797      AE       00         0.0  1.0 6.836      AF       00         0.0  1.0 6.875      B0       40         0.25 0.75 6.914      B1       40         0.25 0.75 6.953      B2       40         0.25 0.75 6.992      B3       40         0.25 0.75 7.031      B4       40         0.25 0.75 7.070      B5       40         0.25 0.75 7.109      B6       40         0.25 0.75 7.148      B7       40         0.25 0.75 7.187      B8       40         0.25 0.75 7.227      B9       40         0.25 0.75 7.266      BA       40         0.25 0.75 7.305      BB       40         0.25 0.75 7.344      BC       40         0.25 0.75 7.383      BD       40         0.25 0.75 7.422      BE       40         0.25 0.75 7.461      BF       40         0.25 0.75 7.500      C0       80         0.5  0.5 7.539      C1       80         0.5  0.5 7.587      C2       80         0.5  0.5 7.617      C3       80         0.5  0.5 7.656      C4       80         0.5  0.5 7.695      C5       80         0.5  0.5 7.734      C6       80         0.5  0.5 7.773      C7       80         0.5  0.5 7.812      C8       80         0.5  0.5 7.852      C9       80         0.5  0.5 7.891      CA       80         0.5  0.5 7.930      CB       80         0.5  0.5 7.969      CC       80         0.5  0.5 8.008      CD       80         0.5  0.5 8.047      CE       80         0.5  0.5 8.086      CF       80         0.5  0.5 8.125      D0       C0         0.75 0.25 8.164      D0       C0         0.75 0.25 8.203      D2       C0         0.75 0.25 8.242      D3       C0         0.75 0.25 8.281      D4       C0         0.75 0.25 8.320      D5       C0         0.75 0.25 8.359      D6       C0         0.75 0.25 8.398      D7       C0         0.75 0.25 8.437      D8       C0         0.75 0.25 8.477      D9       C0         0.75 0.25 8.516      DA       C0         0.75 0.25 8.555      DB       C0         0.75 0.25 8.594      DC       C0         0.75 0.25 8.633      DD       C0         0.75 0.25 8.672      DE       C0         0.75 0.25 8.711      DF       C0         0.75 0.25 8.750      E0       FF         1.0  0.0 8.789      E1       FF         1.0  0.0 8.828      E2       FF         1.0  0.0 8.867      E3       FF         1.0  0.0 8.906      E4       FF         1.0  0.0 8.945      E5       FF         1.0  0.0 8.984      E6       FF         1.0  0.0 9.023      E7       FF         1.0  0.0 9.062      E8       FF         1.0  0.0 9.102      E9       FF         1.0  0.0 9.141      EA       FF         1.0  0.0 9.180      EB       FF         1.0  0.0 9.219      EC       FF         1.0  0.0 9.258      ED       FF         1.0  0.0 9.299      EE       FF         1.0  0.0 9.336      EF       FF         1.0  0.0 9.375      F0       00         0.0  1.0 9.414      F1       00         0.0  1.0 9.453      F2       00         0.0  1.0 9.492      F3       00         0.0  1.0 9.531      F4       00         0.0  1.0 9.570      F5       00         0.0  1.0 9.609      F6       00         0.0  1.0 9.648      F7       00         0.0  1.0 9.687      F8       00         0.0  1.0 9.727      F9       00         0.0  1.0 9.766      FA       00         0.0  1.0 9.805      FB       00         0.0  1.0 9.844      FC       00         0.0  1.0 9.883      FD       00         0.0  1.0 9.922      FE       00         0.0  1.0 9.961      FF       00         0.0  1.0 ______________________________________ ______________________________________ __________________________________________________________________________ DATA Input PROM `Red` `Green` `Blue` Voltage Address PROM PROM PROM PORTIONS (Volts) (Hex) (Hex) (Hex) (Hex) red green blue __________________________________________________________________________ 0.0   00   FF  00   00  1.0 0.0 0.0 0.039 01   FE  02   00  0.992 0.008 0.0 0.078 02   FC  04   00  0.984 0.016 0.0 0.117 03   FA  06   00  0.976 0.024 0.0 0.156 04   F8  08   00  0.969 0.031 0.0 0.195 05   F6  0A   00  0.961 0.039 0.0 0.234 06   F4  0C   00  0.953 0.047 0.0 0.273 07   F2  0E   00  0.945 0.055 0.0 0.312 08   F0  10   00  0.937 0.063 0.0 0.352 09   EE  12   00  0.930 0.070 0.0 0.391 0A   EC  14   00  0.922 0.078 0.0 0.430 0B   EA  16   00  0.914 0.086 0.0 0.469 0C   E8  18   00  0.906 0.094 0.0 0.508 0D   E6  1A   00  0.899 0.101 0.0 0.547 0E   E4  1C   00  0.891 0.109 0.0 0.586 0F   E2  1E   00  0.883 0.117 0.0 0.625 10   E0  20   00  0.875 0.125 0.0 0.664 11   DE  22   00  0.867 0.133 0.0 0.703 12   DC  24   00  0.859 0.141 0.0 0.742 13   DA  26   00  0.851 0.149 0.0 0.781 14   D8  28   00  0.844 0.156 0.0 0.820 15   D6  2A   00  0.836 0.164 0.0 0.859 16   D4  2C   00  0.828 0.172 0.0 0.898 17   D2  2E   00  0.820 0.180 0.0 0.937 18   D0  30   00  0.812 0.188 0.0 0.977 19   CE  32   00  0.804 0.196 0.0 1.016 1A   CC  34   00  0.796 0.204 0.0 1.055 1B   CA  36   00  0.788 0.212 0.0 1.094 1C   C8  38   00  0.781 0.219 0.0 1.133 1D   C6  3A   00  0.773 0.227 0.0 1.172 1E   C4  3C   00  0.766 0.234 0.0 1.211 1F   C2  3E   00  0.758 0.242 0.0 1.250 20   C0  40   00  0.75 0.25 0.0 1.289 21   BE  42   00  0.742 0.258 0.0 1.328 22   BC  44   00  0.734 0.266 0.0 1.367 23   BA  46   00  0.726 0.274 0.0 1.406 24   B8  48   00  0.719 0.281 0.0 1.445 25   B6  4A   00  0.711 0.289 0.0 1.484 26   B4  4C   00  0.703 0.297 0.0 1.523 27   B2  4E   00  0.695 0.305 0.0 1.562 28   B0  50   00  0.687 0.313 0.0 1.602 29   AE  52   00  0.680 0.320 0.0 1.641 2A   AC  54   00  0.672 0.328 0.0 1.680 2B   AA  56   00  0.664 0.336 0.0 1.719 2C   A8  58   00  0.656 0.344 0.0 1.758 2D   A6  5A   00  0.648 0.352 0.0 1.797 2E   A4  5C   00  0.641 0.359 0.0 1.836 2F   A2  5E   00  0.633 0.367 0.0 1.875 30   A0  60   00  0.625 0.375 0.0 1.914 31   9E  62   00  0.613 0.383 0.0 1.953 32   9C  64   00  0.609 0.391 0.0 1.992 33   9A  66   00  0.602 0.398 0.0 2.031 34   98  68   00  0.594 0.406 0.0 2.070 35   96  6A   00  0.586 0.414 0.0 2.109 36   94  6C   00  0.578 0.422 0.0 2.148 37   92  6E   00  0.570 0.430 0.0 2.187 38   90  70   00  0.562 0.438 0.0 2.227 39   8E  72   00  0.554 0.446 0.0 2.266 3A   8C  74   00  0.547 0.453 0.0 2.305 3B   8A  76   00  0.539 0.461 0.0 2.344 3C   88  78   00  0.531 0.469 0.0 2.389 3D   86  7A   00  0.524 0.476 0.0 2.422 3E   84  7C   00  0.516 0.484 0.0 2.461 3F   82  7E   00  0.508 0.492 0.0 2.500 40   80  80   00  0.5 0.5 0.0 2.539 41   7C  84   00  0.484 0.516 0.0 2.578 42   78  88   00  0.469 0.531 0.0 2.617 43   74  8C   00  0.453 0.547 0.0 2.656 44   70  90   00  0.437 0.563 0.0 2.695 45   6C  94   00  0.422 0.578 0.0 2.734 46   68  98   00  0.406 0.594 0.0 2.773 47   64  9C   00  0.391 0.609 0.0 2.812 48   60  A0   00  0.375 0.625 0.0 2.852 49   5C  A4   00  0.359 0.641 0.0 2.891 4A   58  A8   00  0.344 0.656 0.0 2.930 4B   54  AC   00  0.328 0.672 0.0 2.969 4C   50  B0   00  0.312 0.688 0.0 3.008 4D   4C  B4   00  0.297 0.703 0.0 3.047 4E   48  B8   00  0.281 0.719 0.0 3.086 4F   44  BC   00  0.266 0.734 0.0 3.125 50   40  C0   00  0.25 0.75 0.0 3.164 51   3C  C4   00  0.234 0.766 0.0 3.203 52   38  C8   00  0.219 0.781 0.0 3.242 53   34  CC   00  0.203 0.797 0.0 3.281 54   30  D0   00  0.187 0.813 0.0 3.320 55   2C  D4   00  0.172 0.828 0.0 3.359 56   28  D8   00  0.156 0.844 0.0 3.398 57   24  DC   00  0.141 0.859 0.0 3.437 58   20  E0   00  0.125 0.875 0.0 3.477 59   1C  E4   00  0.109 0.891 0.0 3.516 5A   18  E8   00  0.094 0.906 0.0 3.555 5B   14  EC   00  0.078 0.922 3.594 5C   10  F0   00  0.062 0.938 0.0 3.633 5D   0C  F4   00  0.047 0.953 0.0 3.672 5E   08  F8   00  0.031 0.967 0.0 3.711 5F   04  FC   00  0.016 0.984 0.0 3.750 60   00  FF   00  0.0 1.0 0.0 3.789 61   00  F8   08  0.0 0.969 0.031 3.828 62   00  F0   10  0.0 0.937 0.063 3.867 63   00  E8   18  0.0 0.906 0.094 3.906 64   00  E0   20  0.0 0.875 0.125 3.945 65   00  D8   28  0.0 0.844 0.156 3.984 66   00  D0   30  0.0 0.812 0.188 4.023 67   00  C8   38  0.0 0.781 0.219 4.062 68   00  C0   40  0.0 0.75 0.25 4.102 69   00  B8   48  0.0 0.719 0.281 4.141 6A   00  B0   50  0.0 0.687 0.313 4.178 6B   00  A8   58  0.0 0.656 0.344 4.219 6C   00  A0   60  0.0 0.625 0.375 4.258 6D   00  98   68  0.0 0.594 0.406 4.299 6E   00  90   70  0.0 0.562 0.438 4.336 6F   00  88   78  0.0 0.531 0.469 4.375 70   00  80   80  0.0 0.5 0.5 4.414 71   00  78   88  0.0 0.469 0.531 4.453 72   00  70   90  0.0 0.437 0.563 4.492 73   00  68   98  0.0 0.406 0.594 4.531 74   00  60   A0  0.0 0.375 0.625 4.570 75   00  58   A8  0.0 0.344 0.656 4.609 76   00  50   B0  0.0 0.312 0.688 4.648 77   00  48   B8  0.0 0.281 0.719 4.687 78   00  40   C0  0.0 0.25 0.75 4.727 79   00  38   C8  0.0 0.219 0.781 4.766 7A   00  30   D0  0.0 0.187 0.813 4.805 7B   00  28   D8  0.0 0.156 0.844 4.844 7C   00  20   E0  0.0 0.125 0.875 4.883 7D   00  18   E8  0.0 0.094 0.906 4.922 7E   00  10   F0  0.0 0.062 0.938 4.961 7F   00  08   F8  0.0 0.031 0.967 5.000 80   00  00   FF  0.0 0.0 1.0 5.039 81   04  00   FC  0.016 0.0 0.984 5.078 82   08  00   F8  0.031 0.0 0.969 5.117 83   0C  00   F4  0.047 0.0 0.953 5.156 84   10  00   F0  0.063 0.0 0.937 5.195 85   14  00   EC  0.078 0.0 0.922 5.234 86   18  00   E8  0.094 0.0 0.906 5.273 87   1C  00   E4  0.109 0.0 0.891 5.312 88   20  00   E0  0.125 0.0 0.875 5.352 89   24  00   DC  0.141 0.0 0.859 5.391 8A   28  00   D8  0.156 0.0 0.844 5.430 8B   2C  00   D4  0.172 0.0 0.828 5.469 8C   30  00   D0  0.188 0.0 0.812 5.508 8D   34  00   CC  0.2 0.0 0.8 5.547 8E   38  00   C8  0.219 0.0 0.781 5.586 8F   3C  00   C4  0.234 0.0 0.766 5.625 90   40  00   C0  0.25 0.0 0.75 5.664 91   44  00   BC  0.266 0.0 0.734 5.703 92   48  00   B8  0.281 0.0 0.719 5.742 93   4C  00   B4  0.297 0.0 0.703 5.781 94   50  00   B0  0.313 0.0 0.687 5.820 95   54  00   AC  0.328 0.0 0.672 5.859 96   58  00   A8  0.344 0.0 0.656 5.898 97   5C  00   A4  0.359 0.0 0.641 5.937 98   60  00   A0  0.375 0.0 0.625 5.977 99   64  00   9C  0.391 0.0 0.609 6.016 9A   68  00   98  0.406 0.0 0.594 6.055 9B   6C  00   94  0.422 0.0 0.578 6.094 9C   70  00   90  0.438 0.0 0.562 6.133 9D   74  00   8C  0.453 0.0 0.547 6.172 9E   78  00   88  0.469 0.0 0.531 6.211 9F   7C  00   84  0.484 0.0 0.516 6.250 A0   80  00   80  0.5 0.0 0.5 6.289 A1   84  00   7C  0.516 0.0 0.484 6.328 A2   88  00   78  0.531 0.0 0.469 6.367 A3   8C  00   74  0.547 0.0 0.453 6.406 A4   90  00   70  0.563 0.0 0.437 6.445 A5   94  00   6C  0.578 0.0 0.422 6.484 A6   98  00   68  0.594 0.0 0.406 6.524 A7   9C  00   64  0.609 0.0 0.391 6.562 A8   A0  00   60  0.625 0.0 0.375 6.602 A9   A4  00   5C  0.641 0.0 0.359 6.641 AA   A8  00   58  0.656 0.0 0.344 6.680 AB   AC  00   54  0.672 0.0 0.328 6.719 AC   B0  00   50  0.688 0.0 0.312 6.758 AD   B4  00   4C  0.703 0.0 0.297 6.797 AE   B8  00   48  0.719 0.0 0.281 6.836 AF   BC  00   44  0.734 0.0 0.266 6.875 B0   C0  00   40  0.75 0.0 0.25 6.914 B1   C4  00   3C  0.766 0.0 0.234 6.953 B2   C8  00   38  0.781 0.0 0.219 6.992 B3   CC  00   34  0.797 0.0 0.203 7.031 B4   D0  00   30  0.813 0.0 0.187 7.070 B5   D4  00   2C  0.828 0.0 0.172 7.109 B6   D8  00   28  0.844 0.0 0.156 7.148 B7   DC  00   24  0.859 0.0 0.141 7.187 B8   E0  00   20  0.875 0.0 0.125 7.227 B9   E4  00   1C  0.891 0.0 0.109 7.266 BA   E8  00   18  0.906 0.0 0.094 7.305 BB   EC  00   14  0.922 0.0 0.078 7.344 BC   F0  00   10  0.938 0.0 0.062 7.383 BD   F4  00   0C  0.953 0.0 0.047 7.422 BE   F8  00   08  0.967 0.0 0.031 7.461 BF   FC  00   04  0.984 0.0 0.016 __________________________________________________________________________

## Claims

1. A measuring device comprising: measured value of the signal, said means for measuring including an RMS converter, for measuring an RMS value of the signal, and a mean average value converter, for measuring a mean average value of the signal; selecting, when said first switch is in its first position, said RMS converter, and for selecting, when said first switch is in its second position, said mean average value converter; said means for exhibiting being responsive to said output data for providing a digital indication of the measured value of the signal, said means for exhibiting having a color control input for controlling color of said digital indication, in accordance with a first color control signal and a second color control signal; switch being aligned with said first switch, for coupling said first color control signal to said control input when said second switch is in its first position, for illuminating said digital indication in said first color, and for coupling said second color control signal to said color control input when said second switch is in its second position, for illuminating said digital indication in said second color.

2. A measuring device comprising: measured value of the signal, said means for measuring including an RMS converter, for measuring an RMS value of the signal, and a mean average value converter, for measuring a mean average value of the signal; selecting, when said first switch is in its first position, said RMS converter, and for selecting, when said first switch is in its second position, said mean average value converter; a first color and in a second color, said display being responsive to said output data for providing a digital indication of the measured value of the signal, said display having a color control input for controlling color of said digital indication, in accordance with a first color control signal and a second color control signal; switch being aligned with said first switch, for coupling said first color control signal to said control input when said second switch is in its first position, for illuminating said digital indication in said first color, and for coupling said second color control signal to said color control input when said second switch is in its second position, for illuminating said digital indication in said second color.