7seg - History

History

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). In 1910, a seven-segment display illuminated by incandescent bulbs was used on a power-plant boiler room signal panel. They did not achieve widespread use until the advent of LEDs in the 1970s.

They are 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.

For many applications, dot-matrix LCDs have largely superseded LED displays, though even in LCDs 7-segment displays are very common.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.