Seven-segment display
|
|
A seven-segment display (sometimes written as 7-segment display) is a form of display that predates the now ubiquitous 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.
Concept and visual structure
Sevensegment.jpg
A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce standardized representations of the arabic numerals.
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are also fourteen-segment displays and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot-matrix displays.
Usually, but not always, 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:
AAAA F B F B F B GGGG E C E C E C DDDD DP
where the optional DP decimal point (an "eighth segment") is used for the display of non-integer numbers.
In addition to the ten numerals, seven segment displays can produce some latin letters: uppercase A, B, C, E, F, 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. Some of these shapes, however, are visually highly ambiguous and rely on context and the experience of the reader to be properly understood and distinguished from each other. On a related note, school children and students have been known to produce letters and words from upside-down calculator displays.
Implementations
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. An alternative to the 7-segment display in the 1950s through the 1970s was the vacuum tube-like nixie tube. Integrated displays also exist, with 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.
Seven_segment_display-animated.gif
Seven segment displays can be found in patents as early as 1908 (United States patent 974943, for example), but did not achieve widespread use until the advent of LEDs and LCDs 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 a 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, make seven-segment multiple-digit LCD displays very common on basic calculators.