SEVEN SEGMENT DISPLAY

A seven-segment display (SSD), is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix display displays. Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic devices for displaying numerical information.

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

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 numerals. 

  

In a simple LED package, typically all of the cathodes (negative terminals) or all of the anodes (positive terminals) of the segment LEDs are connected and brought out to a common pin; this is referred to as a "common cathode" or "common anode" device. 

Common cathode has all the cathodes of the 7-segments connected directly together and the common anode has all the anodes of the 7-segments connected together.  The anode of a device is the terminal where current flows in from outside. The cathode of a device is the terminal where current flows out.

TRUTH TABLE ON HOW TO IMPLEMENT A SEVEN SEGMENT DISPLAY