7-segment LED Display

A 7 Segment LED Display or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays.

7 segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information.

7 Segment LED Display consists of seven LEDs arranged in a rectangular fashion as shown. Each of the seven LEDs is called a segment because when illuminated the segment forms part of a numerical digit (both Decimal and Hex) to be displayed. An additional 8th LED is sometimes used within the same package thus allowing the indication of a decimal point, (DP) when two or more 7-segment displays are connected together to display numbers greater than ten.

The displays common pin is generally used to identify which type of 7 segment display it is. As each LED has two connecting pins, one called the “Anode” and the other called the “Cathode”, there are therefore two types of LED 7-segment display called: Common Cathode (CC) and Common Anode (CA).

7 segment led display

Common Cathode (CC)

In the common cathode display, all the cathode connections of the LED segments are joined together to logic “0” or ground. The individual segments are illuminated by application of a “HIGH”, or logic “1” signal via a current limiting resistor to forward bias the individual Anode terminals (a-g).
Seven-segment LED display Common Cathode


Common Anode (CA)

In the common anode display, all the anode connections of the LED segments are joined together to logic “1”. The individual segments are illuminated by applying a ground, logic “0” or “LOW” signal via a suitable current limiting resistor to the Cathode of the particular segment (a-g).

Seven-segment LED display Common Anode

7 Segment LED Display working

Display Driver

7-segment Displays are usually driven by a special type of integrated circuit (IC) commonly known as a 7-segment decoder/driver, such as the CMOS 4511. This 7-segment display driver which is known as a Binary Coded Decimal or BCD to 7-segment display decoder and driver, is able to illuminate both common anode or common cathode displays. But there are many other single and dual display drivers available such as the very popular TTL 7447, SN7446AN.

Why to use Display Driver ?

  • Display driver requires only 4 pins of microcontroller to drive the 7-segment display.
  • We do not need to convert decimal numbers into 7 segment display format (from 0-9). We just need to provide BCD (Binary Coded Decimal) numbers and it will take care rest of seven segment conversion.
  • No external Resistor is required.
  • It makes easy to interface with microcontroller.

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