Common Cathode 7 Segment Display

A common cathode 7 Segment LED Display is a 7 segment display in which all the cathode leads of the LEDs are wired (common) together.

LED Types

When it comes to how 7 segment displays are wired, there are 2 types. There are either common anode LED displays or common cathode LED displays.

LED Leads

To better understand this topic, LEDs are 2-lead devices, meaning they have 2 leads. One lead is the anode and the other lead is the cathode. The anode is the side which receives positive voltage and the cathode is the side which is connects to the negative voltage or ground of the circuit. This is shown below:

In a common cathode 7 segment display, all of the cathode pins are tied together, meaning they are common.

Below is a typical LED display, with each LED segment labeled with an alphabetical character.

This is how the seven segment display will appear wired up in a common cathode setup:

As you can see, all of the positive terminals of the seven segment display are all separate. In order to turn any of the segments on, you supply votlage to the terminal that you want turned on. In order to turn, LED a and b on, you supply each with the necessary. However, on the cathode side, you do not have connect each individual LED to ground. The grounds of the LEDs are all tied together. So once you connect the common ground pin, all of the LEDs are connected to ground. This is a common cathode seven segment LED display.