Seven-segment display

A seven-segment display (abbreviation: "7-seg(ment) display"), less commonly known as a seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.

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

Concept and visual structure

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 Arabic numerical . Often the seven segments are arranged in an oblique (slanted) arrangement, which aids readability.

Each of the numbers o,6,7 and 9 may be represented by two or more different glyphs on seven-segment displays.

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

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are also fourteen-segment displays and sixteen-segment displays (for full alphanumeric); however, these have mostly been replaced by dot-matrix displays.

The segments of a 7-segment display are referred to by the letters A to G, as shown to the right, where the optional DP decimal point (an "eighth segment") is used for the display of non-integer numbers.

The animation to the left cycles through the common glyphs of the ten decimal numerals and the six hexadecimal "letter digits" (A–F). It is an image sequence of a "LED" display, which is described technology-wise in the following section. Notice the variation between uppercase and lowercase letters for A–F; this is done to obtain a unique, unambiguous shape for each letter.

Seven segments are, effectively, the fewest required to represent each of the ten Hindu-Arabic numerals with a distinct and recognizable glyph. Blogger have experimented with six-segment and even five-segment displays with such novel shapes as curves, angular blocks and serifs for segments; however, these often require complicated and/or non-uniform shapes and sometimes create unrecognizable glyphs.

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, O, P, S, U, Y, Z, and lowercase a, b, c, d, g, h, i, n, o, q, r, t, u. Thus, ad hoc and corporate solutions dominate the field of alphabetic on seven-segment displays, which is usually not considered essential and only used for basic notifications, such as internal test messages on equipment under development.

Similar displays with fourteen or sixteen segments are available allowing decent representations of the alphabet.

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".

Numbers to 7-segment-code

A single byte can encode the full state of a 7-segment-display. The most popular bit encodings are gfedcba and abcdefg - both usually assume 0 is off and 1 is on.

This table gives the hexadecimal encodings for displaying the digits 0 to 9:

Digit	gfedcba	abcdefg	a	b	c	d	e	f	g
0	0x3F	0x7E	on	on	on	on	on	on	off
1	0x06	0x30	off	on	on	off	off	off	off
2	0x5B	0x6D	on	on	off	on	on	off	on
3	0x4F	0x79	on	on	on	on	off	off	on
4	0x66	0x33	off	on	on	off	off	on	on
5	0x6D	0x5B	on	off	on	on	off	on	on
6	0x7D	0x5F	on	off	on	on	on	on	on
7	0x07	0x70	on	on	on	off	off	off	off
8	0x7F	0x7F	on	on	on	on	on	on	on
9	0x6F	0x7B	on	on	on	on	off	on	on