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A seven-segment display is a form of electronic
display device A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signal ...
for displaying
decimal The decimal numeral system (also called the base-ten positional numeral system and denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers of the Hindu–Arabic nu ...
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.


History

Seven-segment representation of figures can be found in
patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling disclo ...
s as early as 1903 (in ), 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 (). In 1910, a seven-segment display illuminated by incandescent bulbs was used on a power-plant boiler room signal panel. They were also used to show the dialed telephone number to operators during the transition from manual to automatic telephone dialing. They did not achieve widespread use until the advent of
LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s in the 1970s. Some early seven-segment displays used incandescent filaments in an evacuated bulb; they are also known as numitrons. A variation (minitrons) made use of an evacuated potted box. Minitrons are filament segment displays that are housed in DIP packages like modern LED segment displays. They may have up to 16 segments. 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. Vacuum fluorescent display versions were also used in the 1970s. Many early (c. 1970s) LED seven-segment displays had each digit built on a single
die Die, as a verb, refers to death, the cessation of life. Die may also refer to: Games * Die, singular of dice, small throwable objects used for producing random numbers Manufacturing * Die (integrated circuit), a rectangular piece of a semicondu ...
. This made the digits very small. Some included magnifying lenses onto the design in an attempt to make the digits more legible. 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 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 integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...
. In contrast, the shapes of LED segments tend to be simple
rectangle In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°); or a parallelogram contain ...
s, reflecting the fact that they have to be physically moulded to shape, which makes it difficult to form more complex shapes than the segments of 7-segment displays. However, the high recognition factor 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".


Implementations

Seven-segment displays may use a
liquid crystal display A liquid-crystal display (LCD) is a flat panel display, flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liqui ...
(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 (Panaplex), vacuum fluorescent (VFD), incandescent filaments (Numitron), and others. For
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic ...
price totems and other large signs,
vane display A vane display is a type of 7-segment display. Unlike LED and VFD segmented displays, vane displays are composed of seven physical surfaces (vanes), typically painted white, but occasionally other colors, such as yellow or fluorescent green. If ...
s made up of electromagnetically flipped light-reflecting segments (or "vanes") 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 ' that used incandescent filaments arranged into a seven-segment display. In USSR, the first electronic calculator "Vega", which was produced from 1964, contains 20 decimal digits with seven-segment
electroluminescent display Electroluminescent Displays (ELDs) are a type of flat panel display created by sandwiching a layer of electroluminescent material such as GaAs between two layers of conductors. When current flows, the layer of material emits radiation in the form ...
. 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. 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. 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).


Characters

The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top, middle, and bottom. Often the rectangle is '' oblique'' (slanted), which aids readability. In most applications, the segments are of nearly uniform shape and size (usually elongated hexagons, though trapezoids and
rectangle In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°); or a parallelogram contain ...
s can also be used), though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends in an effort to further enhance readability. The seven elements of the display can be lit in different combinations to represent the Arabic numerals. The segments are referred to by the letters A to G, where the optional decimal point (an "eighth segment", referred to as DP) is used for the display of non-integer numbers. A single byte can encode the full state of a 7-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".


Decimal

The
numerical digit A numerical digit (often shortened to just digit) is a single symbol used alone (such as "2") or in combinations (such as "25"), to represent numbers in a positional numeral system. The name "digit" comes from the fact that the ten digits (Latin ...
s 0 to 9 are the most common characters displayed on seven-segment displays. The most common patterns used for each of these is: : Alternate 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':For example the fx-50F calculator from Casio and other models from the same manufacturer. : 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. The official reference shows the less-common four-segment "7". The characters as displayed by your browser:


Hexadecimal

Four binary bits are needed to specify the numbers 0–9, but can also specify 10–15, so usually decoders with 4 bit inputs can also display
Hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
(Hex) digits. Today, a combination of uppercase and lowercase letters is commonly used for A–F; this is done to obtain a unique, unambiguous shape for each hexadecimal digit (otherwise, a capital "D" would look identical to a '0' and a capital 'B' would look identical to an '8'). Also the digit '6' must be displayed with the top bar lit to avoid ambiguity with the letter 'b'. :


Letters

Most letters of the Latin alphabet can be reasonably implemented using seven segments. Though not every letter is available, it is possible to create many useful words. By choosing better
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
s, it is possible to work around many shortcomings of seven-segment alphabet encodings. Some uppercase letters ('I', "O", "S", "Z") look identical to numerical digits ('1', '0', '5', '2'), though it is possible to use lower-case "o" and "i", or putting "I" on the left. Lowercase letters "b" and "q" are identical to the alternate numerical digits '6' and '9'. Depending on the situation, some of these problem characters can be used when no numeric values are used in the same word/phrase, see examples below. Short messages giving status information (e.g. "no dISC" on a CD player) are also commonly represented on 7-segment displays. In the case of such messages it is not necessary for every letter to be unambiguous, merely for the words as a whole to be readable. Examples: :, , , , , :, , , , , , :, , , , , Seven-segment displays have also been used to show letters of the Cyrillic and
Greek alphabet The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BCE. It is derived from the earlier Phoenician alphabet, and was the earliest known alphabetic script to have distinct letters for vowels as ...
s: There are enough patterns to show all the letters but few representations are unambiguous and intuitive at the same time. When all letters need to be displayed on a device, sixteen-segment and dot matrix displays are better choices than seven-segment displays.


Punctuation

Seven segments are capable of displaying some
punctuation Punctuation (or sometimes interpunction) is the use of spacing, conventional signs (called punctuation marks), and certain typographical devices as aids to the understanding and correct reading of written text, whether read silently or aloud. A ...
glyph characters. The
hex Hex or HEX may refer to: Magic * Hex, a curse or supposed real and potentially supernaturally realized malicious wish * Hex sign, a barn decoration originating in Pennsylvania Dutch regions of the United States * Hex work, a Pennsylvania Dutch ...
value for each
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...
character is shown.


Decoder ICs

In the past, some seven-segment decoder
ICs ICS may refer to: Computing * Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy * Industrial control system, computer systems and networks used to control industrial plants and infrastructu ...
didn't output the following modern decimal/hexadecimal font. : * For "1", the MC14558B displays the number on the left side of the display using segments "e" and "f" instead of the usual "b" and "c". * For "7", the TC5022 displays it with additional segment "f". * For "6" and "9", the CD4511B, MC14558B, TC5002, SN74x46/SN74x47/SN74x48/SN74x49 displays both numbers without a "tail", where "x" is the TTL logic family. * For "A" to "F": :* BCD decoder ICs support various seven-segment fonts for their decoded output of "A" (10) to "F" (15) inputs. :* The 7446/7447/7448/7449 and the
Siemens Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad. The principal divisions of the corporation are ''Industry'', '' ...
FLH551-7448/555-8448 chips used truncated versions of "2", "3", "4", "5" and "6" for digits A–E. Digit F (1111 binary) was blank. :* The TC5002 and TC5022 repeat the numbers 0 to 5 for digits A–F. :* The MM74C912 displayed "o" for A and B, "−" for C, D and E, and blank for F. The CD4511B just displayed blanks. :* Soviet programmable calculators like the Б3–34 used the symbols "−", "L", "C", "Г", "E", and " " (space), allowing the error message EГГ0Г to be displayed. :


See also

There are also fourteen- and sixteen-segment displays (for full
alphanumeric Alphanumericals or alphanumeric characters are a combination of alphabetical and numerical characters. More specifically, they are the collection of Latin letters and Arabic digits. An alphanumeric code is an identifier made of alphanumeric ...
s); however, these have mostly been replaced by dot matrix displays. Twenty-two-segment displays capable of displaying the full
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...
character set were briefly available in the early 1980s but did not prove popular. *
Eight-segment display An eight-segment display is a type of display based on eight segments that can be turned on or off according to the font pattern to be produced. It is similar to a nine-segment display whose middle vertical bars are vertical, except that on an e ...
* Nine-segment display * Fourteen-segment display * Sixteen-segment display * Dot matrix display * Nixie tube display * Vacuum fluorescent display


References


External links


Interactive Demonstration of a Seven Segment Display



Interfacing 7 Segment Display with AVR Microcontroller
{{Display technology Display technology