A seven-segment display is a set of seven bar-shaped LED (light-emitting diode) or LCD (liquid crystal display) elements, arranged to form a squared-off figure 8. A few seven-segment displays use other illumination devices, such as incandescent or gas-plasma ("neon") lamps. If all elements are activated, the display shows a numeral 8. When some of the elements are activated but not others, any single-digit numeral from 0 to 9, as well as most uppercase and lowercase letters of the English alphabet, can be portrayed.
Seven-segment displays are commonly used in digital clocks, clock radios, timers, wristwatches, and calculators. They can also be found in motor-vehicle odometers, speedometers, radio frequency indicators, and practically any other display that makes use of alphanumeric characters alone (without the need for graphics). Some seven-segment displays produce an "italicized" (slanted) set of characters.
Individual seven-segment display packages are available from a variety of vendors. Most take the form of rectangular boxes with protruding pins, with an appearance similar to that of an IC (integrated circuit) package, but larger. Some seven-segment displays include a decimal point (a small, dot-shaped element) to the lower right of the bar-shaped segments, so in fact the face of the package contains eight independent elements. A few seven-segment displays have even more dot-shaped elements to portray time in hour-and-minute format, e.g., 12:30. Multiple packages can be arranged in a horizontal row to render large decimal numbers, abbreviations, acronyms, and short words.
The seven-segment concept is more than a century old. One of the earliest records of its use dates back to an electric power plant in the year 1910. That display comprised a large matrix of incandescent bulbs arranged in seven rows. The bulbs could be switched on and off, row by row, to inform engineers about the condition of the system.
Continue reading about seven-segment display:
Instructables describes some experiments you can do with seven-segment displays.