A seven-segment display is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays.
Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information. [1]
Seven-segment representation of figures can be found in patents as early as 1903 (in U.S. patent 1,126,641 ), when Carl Kinsley invented a method of telegraphically transmitting letters and numbers and having them printed on tape in a segmented format. In 1908, F. W. Wood invented an 8-segment display, which displayed the number 4 using a diagonal bar ( U.S. patent 974,943 ). In 1910, a seven-segment display illuminated by incandescent bulbs was used on a power-plant boiler room signal panel. [2] They were also used to show the dialed telephone number to operators during the transition from manual to automatic telephone dialing. [3] They did not achieve widespread use until the advent of LEDs in the 1970s.
Some early seven-segment displays used incandescent filaments in an evacuated bulb; they are also known as numitrons. [4] A variation (minitrons) made use of an evacuated potted box. Minitrons are filament segment displays that are housed in DIP (dual in-line package) packages like modern LED segment displays. They may have up to 16 segments. [5] [6] [7] There were also segment displays that used small incandescent light bulbs instead of LEDs or incandescent filaments. These worked similarly to modern LED segment displays. [8]
Vacuum fluorescent display versions were also used in the 1970s. [9]
Many early (c. 1970s) LED seven-segment displays had each digit built on a single die. This made the digits very small. Some included magnifying lenses in the design to try to make the digits more legible. [10] [11] Other designs used 1 or 2 dies for every segment of the display. [12] [13]
The seven-segment pattern is sometimes used in posters or tags, where the user either applies color to pre-printed segments, or applies color through a seven-segment digit template, to compose figures such as product prices or telephone numbers.
For many applications, dot-matrix liquid-crystal displays (LCDs) have largely superseded LED displays in general, though even in LCDs, seven-segment displays are common. Unlike LEDs, the shapes of elements in an LCD panel are arbitrary since they are formed on the display by photolithography. In contrast, the shapes of LED segments tend to be simple rectangles, because they have to be physically moulded to shape, which makes it difficult to form more complex shapes than the segments of seven-segment displays. However, the easy recognition of seven-segment displays, and the comparatively high visual contrast obtained by such displays relative to dot-matrix digits, makes seven-segment multiple-digit LCD screens very common on basic calculators.
The seven-segment display has inspired type designers to produce typefaces reminiscent of that display (but more legible), such as New Alphabet, "DB LCD Temp", "ION B", etc.
Using a restricted range of letters that look like (upside-down) digits, seven-segment displays are commonly used by school children to form words and phrases using a technique known as "calculator spelling".
Seven-segment displays may use a liquid-crystal display (LCD), a light-emitting diode (LED) for each segment, an electrochromic display, or other light-generating or -controlling techniques such as cold cathode gas discharge (neon) (Panaplex), vacuum fluorescent (VFD), incandescent filaments (Numitron), and others. For gasoline price totems and other large signs, electromechanical seven-segment displays made up of electromagnetically flipped light-reflecting segments are still commonly used. A precursor to the 7-segment display in the 1950s through the 1970s was the cold-cathode, neon-lamp-like nixie tube. Starting in 1970, RCA sold a display device known as the Numitron that used incandescent filaments arranged into a seven-segment display. [14] In USSR, the first electronic calculator "Vega", which was produced from 1964, contains 20 decimal digits with seven-segment electroluminescent display. [15]
In a simple LED package, typically all of the cathodes (negative terminals) or all of the anodes (positive terminals) of the segment LEDs are connected and brought out to a common pin; this is referred to as a "common cathode" or "common anode" device. [16] Hence a 7 segment plus decimal point package will only require nine pins, though commercial products typically contain more pins, and/or spaces where pins would go, in order to match standard IC sockets. Integrated displays also exist, with single or multiple digits. Some of these integrated displays incorporate their own internal decoder, though most do not: each individual LED is brought out to a connecting pin as described.
Multiple-digit LED displays as used in pocket calculators and similar devices used multiplexed displays to reduce the number of I/O pins required to control the display. For example, all the anodes of the A segments of each digit position would be connected together and to a driver circuit pin, while the cathodes of all segments for each digit would be connected. To operate any particular segment of any digit, the controlling integrated circuit would turn on the cathode driver for the selected digit, and the anode drivers for the desired segments; then after a short blanking interval the next digit would be selected and new segments lit, in a sequential fashion. In this manner an eight digit display with seven segments and a decimal point would require only 8 cathode drivers and 8 anode drivers, instead of sixty-four drivers and IC pins. [17] Often in pocket calculators the digit drive lines would be used to scan the keyboard as well, providing further savings; however, pressing multiple keys at once would produce odd results on the multiplexed display.
Although to a naked eye all digits of an LED display appear lit, only one digit is lit at any given time in a multiplexed display. The digit changes at a high enough rate that the human eye cannot see the flashing (on earlier devices it could be visible to peripheral vision).
The seven segments are arranged as a rectangle, with two vertical segments on each side and one horizontal segment each at the top, middle, and bottom. Often the rectangle is oblique (slanted), which may aid readability. In most applications, the segments are of nearly uniform shape and size (usually elongated hexagons, though trapezoids and rectangles can also be used); though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends, to try to make them more easily readable. The seven elements of the display can be lit in different combinations to represent each of the Arabic numerals.
The individual segments are referred to by the letters "a" to "g", and an optional decimal point (an "eighth segment", referred to as DP) is sometimes used for the display of non-integer numbers. [18] [16] A single byte can encode the full state of a seven-segment display, including the decimal point. The most popular bit encodings are gfedcba and abcdefg. In the gfedcba representation, a byte value of 0x06 would turn on segments "c" and "b", which would display a "1".
The numerical digits 0 to 9 are the most common characters displayed on seven-segment displays. The most common patterns used for each of these are: [20]
Alternative patterns: The numeral 1 may be represented with the left segments, the numerals 6 and 9 may be represented without a "tail", and the numeral 7 represented with a 'tail': [21]
In Unicode 13.0, 10 codepoints had been given for segmented digits 0–9 in the Symbols for Legacy Computing block, to replicate early computer fonts that included seven-segment versions of the digits. [22] The official reference shows the less-common four-segment "7".
The binary-coded decimal (BCD) 0 to 9 digit values require four binary bits to hold their values. Since four bits (24) can hold 16 values, this means hexadecimal (hex) digits can be represented by four bits too. [23] Since there are a limited number of segments in seven-segment displays, a couple of the hexadecimal digits are required to be displayed as lowercase letters, otherwise the uppercase letter "B" would be the same as the digit "8", and the uppercase letter "D" would be the same as the digit "0". [24] [25] [26] [27] The digit "6" must also be displayed with the topmost segment as to avoid ambiguity with the letter "b".
Early decoder IC's often produced random patterns or duplicates of digits for 10-15, as they were designed to use as few gates as possible and only required to produce 0-9.
Many letters of the latin alphabet can be reasonably implemented on a seven-segment display. Though not every letter is available, it is possible to create many useful words. By careful choice of words, one can sometimes work around unavailable letters. Uppercase letters "I", "O", "S", "Z" conflict with the common seven-segment representation of digits "1", "0", 5", "2", and the lowercase letter "g" with digit "9". Upper case I could be put on the left (as lower-case L is shown here) but this is not often done. Lowercase 'b' and 'q' are identical to the alternate numerical digits '6' and '9'.
| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Upper | | | | |  |  | |  |  |  | |  | |  |  | | ||||||||||
| Lower |  | |  | |  | |  |  |  | |  |  | |  |  |  |  |
The following are some real world english word examples seen on actual electronic equipment:
, , , , , , , , , , , , , , , , , 
There are also fourteen- and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot matrix displays. 22-segment displays capable of displaying the full ASCII character set [28] were briefly available in the early 1980s but did not prove popular.
An electronic calculator is typically a portable electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics.
A vacuum tube, electron tube, valve, or tube is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
A Nixie tube, or cold cathode display, is an electronic device used for displaying numerals or other information using glow discharge.
A cold cathode is a cathode that is not electrically heated by a filament. A cathode may be considered "cold" if it emits more electrons than can be supplied by thermionic emission alone. It is used in gas-discharge lamps, such as neon lamps, discharge tubes, and some types of vacuum tube. The other type of cathode is a hot cathode, which is heated by electric current passing through a filament. A cold cathode does not necessarily operate at a low temperature: it is often heated to its operating temperature by other methods, such as the current passing from the cathode into the gas.
The ANITA Mark VII and ANITA Mark VIII calculators were launched simultaneously in late 1961 as the world's first all-electronic desktop calculators. Designed and built by the Bell Punch Co. in Britain, and marketed through its Sumlock Comptometer division, they used vacuum tubes and cold-cathode switching tubes in their logic circuits and nixie tubes for their numerical displays.
A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, producing a phenomenon known as a Townsend discharge. Gases used include mercury vapor, xenon, neon, and hydrogen. Unlike a vacuum tube (valve), a thyratron cannot be used to amplify signals linearly.
The HP-35 was Hewlett-Packard's first pocket calculator and the world's first scientific pocket calculator: a calculator with trigonometric and exponential functions. It was introduced in 1972.
A display device is an output device for presentation of information in visual or tactile form. When the input information that is supplied has an electrical signal the display is called an electronic display.
A vacuum fluorescent display (VFD) is a display device once commonly used on consumer electronics equipment such as video cassette recorders, car radios, and microwave ovens.
4-bit computing is the use of computer architectures in which integers and other data units are 4 bits wide. 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses of that size. A group of four bits is also called a nibble and has 24 = 16 possible values, with a range of 0 to 15.
A fourteen-segment display (FSD) is a type of display based on 14 segments that can be turned on or off to produce letters and numerals. It is an expansion of the more common seven-segment display, having an additional four diagonal and two vertical segments with the middle horizontal segment broken in half. A seven-segment display suffices for numerals and certain letters, but unambiguously rendering the ISO basic Latin alphabet requires more detail. A slight variation is the sixteen-segment display which allows additional legibility in displaying letters or other symbols.
A sixteen-segment display (SISD) is a type of display based on sixteen segments that can be turned on or off to produce a graphic pattern. It is an extension of the more common seven-segment display, adding four diagonal and two vertical segments and splitting the three horizontal segments in half. Other variants include the fourteen-segment display which does not split the top or bottom horizontal segments, and the twenty-two-segment display that allows lower-case characters with descenders.
A dot-matrix display is a low-cost electronic digital display device that displays information on machines such as clocks, watches, calculators, and many other devices requiring a simple alphanumeric display device of limited resolution.
Charlieplexing is a technique for accessing a large number of LEDs, switches, micro-capacitors or other I/O entities, using relatively few tri-state logic wires from a microcontroller. These I/O entities can be wired as discrete components, x/y arrays, or woven in a diagonally intersecting pattern to form diagonal arrays.
In electronics, a Dekatron is a gas-filled decade counting tube. Dekatrons were used in computers, calculators, and other counting-related products during the 1950s and 1960s. "Dekatron" was the brand name used by Ericsson Telephones Limited (ETL), of Beeston, Nottingham and has since become a generic trademark. The device was invented by John Reginald Acton, with the patent assigned to Ericsson.
The various shapes of numerical digits, letters, and punctuation on seven-segment displays is not standardized by any relevant entity. Unicode provides encoding codepoint for segmented digits in Unicode 13.0 in Symbols for Legacy Computing block.
Electrically operated display devices have developed from electromechanical systems for display of text, up to all-electronic devices capable of full-motion 3D color graphic displays. Electromagnetic devices, using a solenoid coil to control a visible flag or flap, were the earliest type, and were used for text displays such as stock market prices and arrival/departure display times. The cathode ray tube was the workhorse of text and video display technology for several decades until being displaced by plasma, liquid crystal (LCD), and solid-state devices such as thin-film transistors (TFTs), LEDs and OLEDs. With the advent of metal–oxide–semiconductor field-effect transistors (MOSFETs), integrated circuit (IC) chips, microprocessors, and microelectronic devices, many more individual picture elements ("pixels") could be incorporated into one display device, allowing graphic displays and video.
Nimo was the trademark of a family of small cathode-ray tube (CRTs) used for numerical displays. They were manufactured by Industrial Electronic Engineers (IEE) around the mid-1960s. The tube had ten electron guns with stencils that shaped the electron beam as digits.
A text display is an electronic alphanumeric display device that is mainly or only capable of showing text, or extremely limited graphic characters. This includes electromechanical split-flap displays, vane displays, and flip-disc displays; all-electronic liquid-crystal displays, incandescent eggcrate displays, LED displays, and vacuum fluorescent displays; and even electric nixie tubes.
