Seven Segment Display
Seven-segment displays are electronic display devices used as an easy way to display decimal numerals and an alternative to the more complex dot-matrix displays. Seven-segment displays first became widely used as a popular way of displaying numbers. They are called segment displays because they are composed of several segments that switch on and off to give the appearance of the desired glyph. The segments are usually single LEDs or liquid crystals. Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, displays in home appliances, cars, and various other electronic devices that display numerical information.
There are two different types of driving seven-segment displays:- the common anode type and the common cathode type. In the common anode type all the anodes on the display are tied to a common pin, typically the power source, and the LEDs are controlled via the cathodes with the ground being on and power being off. In the common cathode type, all the cathodes are tied to a common pin, in this case generally ground, and the LEDs are driven by the state of the anodes where the ground is off and power is on. Hence a seven-segment plus decimal point package will only require nine pins, though commercial products typically contain more pins in order to match industry standard pin outs.
There are several types of segment displays but the most commonly used displays are Seven-segment, Fourteen-segment and Sixteen-segment (7-segment, 14-segment and 16-segment) displays. HD44780 is an LCD controller which is widely accepted protocol for LCDs. Seven-segment displays may use a liquid crystal display (LCD), a light-emitting diode (LED) for each segment, or other light-generating or control techniques such as cold cathode gas discharge (Panaplex), vacuum fluorescent, incandescent filaments (Numitron), and others. For gasoline price totems and other large signs, vane displays made up of electromagnetically flipped light-reflecting segments (or "vanes") is still commonly used.
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