Seven-Segment Displays
A Seven-Segment Display is simply a figure eight grouping of 7 LEDs. With each LED labeled letters a through g. There are two types of LED configurations: Common Cathode Display, in which all the LED cathodes are connected, and Common Anode, in which all the LED anodes are connected.
LEDs are illuminated when its corresponding pin is powered. Using different combinations of LEDs the Seven Segment Display can create a multitude of numbers and some letters.
Multiplexers
A multiplexer is a digital switch that has multiple inputs and a single output. There are four types of multiplexers: 2-to-1, 4-to-1, 8-to-1, and 16-to-1.
De-multiplexers
A de-multiplexer is a digital switch with a single input and multiple outputs. There are four types of de-multiplexers 1-to-2, 1-to-4, 1-to-8, and 1-to-16.