In the common cathode configuration, all the cathodes (negative terminals) of the seven LEDs are connected to a common ground. Display segments are controlled independently by applying a HIGH (Logic 1) voltage to the anode of the particular LED.
Figure 1 shows a seven segment LED display. As indicated by the diode equivalent circuit on the left, each segment is an individual LED. This is a Common Cathode (CC) display. All of the cathodes (or negative terminals) of the segment LEDs are connected together.
In this tutorial, we will have a basic introduction to Seven Segment Displays or 7-Segment Displays. They are commonly used to display digits from 0 to 9 and also few alphabets (usually, A to F).