A segment display is a display device comprising several segments, which switch on and off to give the appearance of digits or alphanumeric characters. The segments are usually single LEDs or liquid crystals. Segment displays are often used in digital watches and pocket calculators. Common types include seven-segment displays (which are used for numerals only) and alphanumeric fourteen-segment displays and sixteen-segment displays (which can display numerals and Latin alphabet letters).
Seven-segment display
A seven-segment display is a display device for digits and some letters. It is often used in a device to display numbers – for example, in a digital clock or calculator. To a lesser extent, but still common, it is used to display alphanumeric information. Since a seven-segment display tends to be less expensive than a display that can better represent any character and even a graphic image such as a dot matrix display, the design choice to use a seven-segment display is a tradeoff to minimize cost over providing richer functionality.
History 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. 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 LEDs 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 (dual in-line package) 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. This made the digits very small. Some included magnifying lenses in the design to try to make the digits more legible. Other designs used 1 or 2 dies for every segment of the display. Liquid-crystal display (LCD) largely superseded LED seven-segment displays. The shapes of elements in an LCD panel are arbitrary since they are formed on the display by photolithography, while 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. 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. Seven-segment displays have been recommended against for critical information (i.e. information that is dangerous to health or safety if misread) due to misreading if upside down or if segments are "stuck" on or off. Backlit dot-matrix LCDs have largely superseded seven-segment displays on such equipment. 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. 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. Seven-segment displays, which use a restricted range of letters that look like (upside-down) digits, are commonly used by school children to form words and phrases using a technique known as "calculator spelling."
… excerpt ends here. Continue reading the full article.
