Seven-segment display character representations
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The topic of seven-segment display character representations revolves around the various shapes of numerical digits, letters, and punctuation devisable on seven-segment displays. Such representation of characters is not standardized by any relevant entity (e.g. ISO, IEEE or IEC).
Two basic conventions are in common use for some Hindu-Arabic numerals: display segment A is optional for digit 6, segment F for 7, and segment D for 9. Although EF could also be used to represent digit 1, this seems to be rarely done if ever.
In addition to the ten digits, seven-segment displays can be used to show letters of the Latin, Cyrillic and Greek alphabets including punctuation, but only very few representations are unambiguous and intuitive at the same time.
Also, alphabetic letters, and many other characters, are much clearer and unambiguously shown on the currently ubiquitous and low-priced dot matrix displays as well as on fourteen-segment and sixteen-segment displays. All this obviates the need for seven-segment displays to show letters in all but the most special cases.
One such special case is the display of the letters A–F when denoting the hexadecimal values (digits) 10–15. These are needed on some scientific calculators, and are used with some test displays on electronic equipment. Although there is no official standard, most devices displaying hex digits use the unique forms shown in the leftmost column of the Latin alphabet section below — uppercase A, C, E, and F, and lowercase b and d.
For the remainder of characters, ad hoc and corporate solutions dominate the field of using seven-segment displays to show general words and phrases. Such applications of seven-segment displays are usually not considered essential and are only used for basic notifications on consumer electronics appliances (as is the case of this article's example phrases), and as internal test messages on equipment under development.
Display pattern Examples
||This section possibly contains original research. (July 2011)|
The tables below show alternative seven-segment display patterns for the Hindu-Arabic numerals. Although the designs for digits are now mostly universal, there is no conventional set for all letters, i.e. ad-hoc solutions prevail, some using two consecutive segment arrays for a single symbol (see 'K', 'M', 'N', 'T', 'V', 'W', 'X') and most employing a unicase design. Hence the patterns shown have been used to various degrees, some are virtually unused. Note that letters are usually left-aligned (chiefly 'uppercase i' but not 'lowercase L' because have down segment on), while the digit one '1' is right-aligned. Sometimes the most intuitive shape may not be used because it was ambiguous with a different character. Some capital letters are impossible, EX: M, X.
The following phrases come from a portable media player's seven-segment display. They give a good illustration of an application where a seven-segment display may be sufficient for displaying letters, since the relevant messages are neither critical nor in any significant risk of being misunderstood, much due to the limited number and rigid domain specificity of the messages. As such, there is no direct need for a more expressive display in this case, although even a slightly wider repertoire of messages would require at least a 9-seg 14- or 16-segment display, if not a dot matrix one.