Seven-segment display

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A seven-segment display (abbreviation: "7-seg(ment) display"), less commonly known as a seven-segment indicator, is a form of display device that is an alternative to the more complex dot-matrix displays. Seven-segment displays are commonly used in electronics as a method of displaying decimal numeric feedback on the internal operations of devices.

1 Concept and visual structure
2 Implementations
3 Alphabetic display
4 Character representations
5 External links

[edit] Concept and visual structure

A typical 7-segment LED display component, with decimal point.

A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the Hindu-Arabic numerals. Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays.

The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot-matrix displays.

Often the seven segments are arranged in an oblique, or italic, arrangement, which aids readability.

The segments of a 7-segment display are referred to by the letters A to G, as follows:

where the optional DP decimal point (an "eighth segment") is used for the display of non-integer numbers.

[edit] Implementations

A mechanical seven segment display for displaying petrol prices.

Most separate 7-segment displays use an array of light-emitting diodes (LEDs), though other types exist using alternative technologies such as cold cathode gas discharge, vacuum fluorescent, incandescent filament, liquid crystal display (LCD), etc. For gas price totems and other large signs, electromagnetically flipped light-reflecting segments (sometimes called "vanes") are still commonly used. An alternative to the 7-segment display in the 1950s through the 1970s was the vacuum tube-like nixie tube.

In a simple LED package, each LED is typically connected with one terminal to its own pin on the outside of the package and the other LED terminal connected in common with all other LEDs in the device and brought out to a shared pin. This shared pin will then make up all of the cathodes (negative terminals) OR all of the anodes (positive terminals) of the LEDs in the device; and so will be either a "Common Cathode" or "Common Anode" device depending how it is constructed. Hence a 7 segment plus DP package will only require nine pins to be present and connected.

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.

LED-based 7-segment display showing the 16 hex digits.

Seven segment displays can be found in patents as early as 1908 (in U.S. Patent 974,943 , F W Wood invented an 8-segment display, which displayed the number 4 using a diagonal bar), but did not achieve widespread use until the advent of LEDs in the 1970s. They are sometimes even used in unsophisticated displays like cardboard "For sale" signs, where the user either applies color to pre-printed segments, or (spray)paints 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, though even in LCDs 7-segment displays are very common. Unlike LEDs, the shapes of elements in an LCD panel are arbitrary since they are formed on the display by a kind of printing process. In contrast, the shapes of LED segments tend to be simple rectangles, 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 common recognition factor of 7-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.

[edit] Alphabetic display

In addition to the ten numerals, seven segment displays can be used to show letters of the latin, cyrillic and greek alphabets including punctuation, but only few representations are unambiguous and intuitive at the same time: uppercase A, B, C, E, F, G, H, I, J, L, N, O, P, S, U, Y, Z, and lowercase a, b, c, d, e, g, h, i, n, ñ, o, q, r, t, u. Detailed tables of alternative seven-segment symbols for letters and punctuation are given in the section Character representations, below.

The representation of digits and/or letters with seven-segment displays is not standardized by any relevant entity (e.g. ISO, IEEE or IEC). Two basic conventions can be seen for digits: one lights the additional segment in six (a), seven (f) and nine (d), the other, more anglophone one does not. Military, mission critical, and safety-of-life applications prefer the latter. The idea is to use a display font such that a single burned out or missing segment in a digit will not display as a different valid digit.

Ad hoc and corporate solutions dominate the field of alphabetic seven-segment display, which is usually not considered essential and only used for basic notifications.

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".

[edit] Character representations

The tables below show alternative seven-segment display patterns for the Arabic numerals, the 26 letters of the English language part of the Latin alphabet, and common related punctuation symbols. See the section Alphabetic display, above, for an overall treatment.

[edit] Digits and punctuation

0
1
2
3
4
5
6
7
8
9
.
,
;
:, =; #
?; ¿
!; ¡
", “, ”; „
', ‘, ’; ‚
-, –, —, −; ¯; _
+; &
/ (÷); \ (*, ·, ×)
(, [, <, {
), ], >, }
°; ′; ″
^; ´; `; ~
§; $

[edit] Latin alphabet

A, a; @
B, b
C, c
D, d
E, e
F, f
G, g
H, h
I, i, ı
J, j
K, k
L, l
M, m
N, n
O, o
P, p
Q, q
R, r
S, s, ſ
T, t
U, u
V, v
W, w
X, x
Y, y
Z, z

[edit] Greek alphabet

Α, α
Β, β, ϐ
Γ, γ
Δ, δ
Ε, ε
Ϝ, ϝ
Ζ, ζ
Η, η
Θ, θ, ϴ, ϑ
Ι, ι
Κ, κ, ϰ
Λ, λ
Μ, μ, µ
Ν, ν
Ξ, ξ
Ο, ο
Π, π, ϖ
Ϙ, ϙ; Ϟ, ϟ
Ρ, ρ, ϱ
Σ, σ, ς, Ϲ, ϲ
Ϛ, ϛ
Τ, τ
Υ, υ
Φ, φ, ϕ
Χ, χ
Ψ, ψ
Ω, ω

[edit] Examples

Media player
On		Off
Open		Close
Play		Pause
Stop		(Play) List
Track		Repeat
Shuffle		Random

Meter
1 millimetre
2 hectares
3 picolitres
π radians
4 kilograms
5 megaamperes
6 microfarads
7 degrees, 8 minutes, 9 seconds
10 petaelectronvolt
11 percent
12 feet
13 mebibyte
14 gigahertz
15 kelvin
16 degrees Reaumur
17 newton-metre
Enter n = x·π