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Seven-segment display

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A typical 7-segment LED display component, with decimal point in a wide DIP-10 package

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]

History

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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.

Filament seven-segment display

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]

A seven-segment display at a gas station

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".

Implementations

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A multiplexed 4-digit, seven-segment display with only 12 pins
A 4-digit display scanning by columns to make the number 1.234
Eight small rectangular blobs, which are the digits, connected by fine hair-like wires to tracks along a circuit board
X-Ray of an 8-digit 7-segment multiplexed LED display from a 1970s calculator

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).

Characters

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Main article: Seven-segment display character representations
Segment names of a seven-segment display with an eighth Decimal Point segment.

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".

16×8 grid showing the 128 states of a seven-segment display[19]

Decimal

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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]

0 1 2 3 4 5 6 7 8 9

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]

1* 6 7 9

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".

Hexadecimal

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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 to ensure they appear uniquely different from numeric digits. 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 be displayed with the topmost segment as 6 to avoid ambiguity with the letter "b".

A b C d E F

Letters

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It is possible to produce legible words on 7-segment displays, though not arbitrary English (or any other language). Some examples seen on actual electronic equipment:

OPEn, CLOSE, PLAY, PAUSE, SHUFFLE, no dISC
StArt, StoP, run, FAIL, Error, SEtUP, HELP
MModE, on, OFF, yES, no, Hot, CoLd

See also

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7-, 9-, 14-, and 16-segment displays shown side by side

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.

References

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  1. ^ "Seven Segment Displays". Archived from the original on 2012-04-04.
  2. ^ Rogers, Warren O. (1910-02-01). "Power Plant Signalling System". Power and the Engineer. 32 (5): 204–206. Archived from the original on 2014-03-31. Retrieved 2016-10-06.
  3. ^ Clark, E. H. (December 1929). "Evolution of the Call-Indicator System" (PDF). Bell Laboratories Record. 8 (5): 171–173. Archived (PDF) from the original on 2024-04-13. Retrieved 2015-12-19.
  4. ^ "IEE Apollo DA-2110 Numitron Tube (DA2110, RCA DR-2110) - Industrial Alchemy". industrialalchemy.org. Archived from the original on 2020-09-15. Retrieved 2020-04-15.
  5. ^ "Wamco KW-105AL Alphanumeric Minitron Display - Industrial Alchemy". industrialalchemy.org. Archived from the original on 2020-09-15. Retrieved 2020-04-15.
  6. ^ "Numitron Tube Tutorial". 2011-12-21. Archived from the original on 2018-09-25. Retrieved 2020-04-14.
  7. ^ "Incandescent Displays – the Vintage Technology Association". Archived from the original on 2018-02-17. Retrieved 2020-04-14.
  8. ^ "Alco MSM-5A Mosaic Indicator Incandescent Display - Industrial Alchemy". industrialalchemy.org. Archived from the original on 2020-09-15. Retrieved 2020-04-15.
  9. ^ "General Electric Y1938 – the Vintage Technology Association". Archived from the original on 2016-06-11. Retrieved 2020-11-13.
  10. ^ "Litronix Surface Mount Wristwatch LED Display – Industrial Alchemy". Archived from the original on 2018-08-31. Retrieved 2020-04-16.
  11. ^ "Litronix DL330 Series LED Displays (Siemens DL340M) - Industrial Alchemy". Archived from the original on 2018-03-04. Retrieved 2020-04-16.
  12. ^ "Soviet AL304V Surface Mount LED - Industrial Alchemy". Archived from the original on 2022-09-28. Retrieved 2024-01-21.
  13. ^ "Texas Instruments TIA8447 LED Display - Industrial Alchemy". Archived from the original on 2022-05-29. Retrieved 2024-01-21.
  14. ^ "Advert for RCA NUMITRON Display Devices". Electronic Design. 22 (12). Hayden: 163. 1974-06-07. Archived from the original on 2014-03-31. Retrieved 2012-06-22.
  15. ^ "Museum of Soviet Calculators - VEGA". 2010-09-29. Archived from the original on 2010-09-29.
  16. ^ a b Elektrotechnik Tabellen Kommunikationselektronik (3rd ed.). Braunschweig, Germany: Westermann Verlag. 1999. p. 110. ISBN 3142250379.
  17. ^ e.g. DCR 1050m Archived 31 March 2014 at the Wayback Machine
  18. ^ "Seven Segment Displays". Archived from the original on 2012-01-05. Retrieved 2012-11-14.
  19. ^ Diehl, H. P.; De Mulder, H. D. (April 1981). "junior cookbook: a few healthy recipes to keep your computer in shape" (PDF). elektor (UK) – up-to-date electronics for lab and leisure. Vol. 1981, no. 72. pp. 4-28 – 4-31 [4-30 Figure 4]. Archived (PDF) from the original on 2020-07-03. Retrieved 2020-07-03.
  20. ^ Nührmann, Dieter (1981). Written at Achim, Bremen, Germany. Werkbuch Elektronik (in German) (3 ed.). Munich, Germany: Franzis-Verlag GmbH. p. 695. ISBN 3-7723-6543-4.
  21. ^ For example the fx-50F calculator from Casio and other models from the same manufacturer.
  22. ^ Official Unicode Consortium code chart Archived 2020-06-05 at the Wayback Machine (PDF)
  23. ^ "Application Note 3210 – Quick-Start: Driving 7-Segment Displays with the MAX6954" (PDF) (Application note) (3 ed.). Maxim Integrated. March 2008 [2004-06-25]. Archived (PDF) from the original on 2017-03-20. Retrieved 2013-05-06.
  24. ^ "Driving 7-Segment Displays". Maxim Integrated. 2004. Archived from the original on 2017-03-20. Retrieved 2017-03-20.
  25. ^ electronic hexadecimal calculator/converter SR-22 (PDF) (Revision A ed.). Texas Instruments Incorporated. 1974. p. 7. 1304-389 Rev A. Archived (PDF) from the original on 2017-03-20. Retrieved 2017-03-20.
  26. ^ electronic calculator – TI programmer (PDF). Texas Instruments Incorporated. 1977. p. 7. Archived (PDF) from the original on 2017-03-28. Retrieved 2017-03-28.
  27. ^ electronic calculator – TI LCD programmer (PDF). Texas Instruments Incorporated. 1981. p. 8. Archived (PDF) from the original on 2017-03-28. Retrieved 2017-03-28.
  28. ^ "DL-3422 4-digit 22-segment alphanumeric Intelligent Display preliminary data sheet". Internet Archive. Litronix 1982 Optoelectronics Catalog. p. 82. Retrieved 2016-09-03.
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