Seven-segment display

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]

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]

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For many applications, dot-matrix liquid-crystal displays (LCDs) have largely superseded LED displays in general, though even in LCDs, seven-segment displays are common.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".

A multiplexed 4-digit, seven-segment display with only 12 pins

A 4-digit display scanning by columns to make the number 1.234

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 (Panaplex), vacuum fluorescent (VFD), incandescent filaments (Numitron), and others. For gasoline price totems and other large signs, vane displays 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 Numitron that used incandescent filaments arranged into a seven-segment display.[12] In USSR, the first electronic calculator "Vega", which was produced from 1964, contains 20 decimal digits with seven-segment electroluminescent display.[13]

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.[14] 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.[15] 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).

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.[16][14] 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[17]

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 careful choice of words, one can sometimes work around many shortcomings of seven-segment alphabet encodings.

Latin alphabet

	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

  Ambiguous with a digit. 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'.

Short messages giving status information (e.g. "" on a CD player) are also commonly represented on seven-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 alphabets:

Cyrillic alphabet

	А	Б	В	Г	Д	Е	Ё	Ж	З	И	Й	К	Л	М	Н	О	П	Р	С	Т	У	Ф	Х	Ц	Ч	Ш	Щ	Ъ	Ы	Ь	Э	Ю	Я
Upper
Lower

  Ambiguous with a digit.

Greek alphabet

	Α	Β	Γ	Δ	Ε	Ζ	Η	Θ	Ι	Κ	Λ	Μ	Ν	Ξ	Ο	Π	Ρ	Σ	Τ	Υ	Φ	Χ	Ψ	Ω
Upper
Lower

  Ambiguous with a digit.

There are enough patterns to show all the letters but few representations are unambiguous and intuitive at the same time.[26] 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 glyph characters.

Punctuation encodings

Glyph	Display	Unicode	Meaning
		0x0020	Space
_		0x005F	Underscore
-		0x002D	Minus, Negative, Hyphen, Dash
‾		0x203E	Overscore, Macron
=		0x003D	Equals
=		0x207C	Superscript equals
≡		0x2261	Triple bar, Identical to, Hamburger button
°		0x00B0	Degree
"		0x0022	Double quote, Double prime
'		0x0027	Apostrophe, Single quote, Prime
( or [		0x005B	Parenthesis, Bracket (conflicts with uppercase C)
) or ]		0x005D	Parenthesis, Bracket
<		0x003C	Less than
>		0x003E	Greater than
?		0x003F	Question mark

The decimal point can be used to add a period after a letter.

In the past, some seven-segment decoder ICs 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".[27]
• For "7", the TC5022 displays it with additional segment "f".[28]
• 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[29] and the Siemens 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.[30][31]
• The TC5002 and TC5022 repeat the numbers 0 to 5 for digits A–F.[28]
• The MM74C912 displayed "o" for A and B, "−" for C, D and E, and blank for F.[32] The CD4511B just displayed blanks.[33]
• Soviet programmable calculators like the Б3–34 used the symbols "−", "L", "C", "Г", "E", and " " (space), allowing the error message EГГ0Г to be displayed.

Manufacturer	Part Number	Production	Description	0	1	2	3	4	5	6	7	8	9	A	B	C	D	E	F	Output	Datasheet
RCA	CD4026B	Active (TI)	BCD Counter, Up																	Active-High	[34]
RCA	CD4033B	Active (TI)	BCD Counter, Up																	Active-High	[34]
RCA	CD40110B	Active (TI)	BCD Counter, Up/Down																	Active-High	[35]
RCA TI	CD4511B CD74x4511	Active (TI)	BCD Decoder, Latch																	Active-High	[33][36]
RCA TI	CD4543B CD74x4543	Active (TI)	BCD Decoder, Latch																	Active-High or Low	[37][38]
Motorola	MC14495-1	Discontinued	Hex Decoder, Latch																	Active-High, 290Ω	[39]
Motorola	MC14558B	Discontinued	BCD Decoder																	Active-High	[27]
TI	SN74LS47	Active	BCD Decoder																	Active-Low	[29]
TI	SN74LS247	Active	BCD Decoder																	Active-Low	[40]
Toshiba	TC5002	Discontinued	BCD Decoder																	Active-High	[28]
Toshiba	TC5022	Discontinued	BCD Decoder																	Active-High	[28]
National	MM74C912	Discontinued	6-Digit BCD Controller																	Active-High	[32]
National	MM74C917	Discontinued	6-Digit Hex Controller																	Active-High	[32]
National	DM9368	Discontinued	Hex Decoder, Latch																	Active High, 25mA CC	[41]
National	DM9370	Discontinued	Hex Decoder, Latch																	Active Low, OC	[42]
National	DM9374	Discontinued	BCD Decoder, Latch																	Active Low, 15mA CC	[43]

NOTE: the "x" in part numbers means logic family, such as "HC" or "HCT".

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[44] were briefly available in the early 1980s but did not prove popular.

• Eight-segment display
• Nine-segment display
• Fourteen-segment display
• Sixteen-segment display
• Dot matrix display
• Nixie tube display
• Vacuum fluorescent display

Wikimedia Commons has media related to Seven segment display.

• Interactive Demonstration of a Seven Segment Display
• Interfacing Seven Segment Display to 8051 Microcontroller
• Interfacing 7 Segment Display with AVR Microcontroller