7-segment-led

7-segment LED Display

A 7 segment LED display is a form of an electronic display device is used for displaying decimal numerals. It is an alternative to previously used more complex dot matrix displays.

They are mainly used in electronic meters, digital clocks, basic calculator, and other electronic devices who 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 segment because when illuminated, the segment forms part of a numerical digit (of both Decimal and Hex) to be displayed.

An additional 8th LED displays the indication of a decimal point(DP). To display numbers greater than ten two or more 7-segment displays are connected together.

The displays common pins are generally used to identify which type of 7 segment display it is.
Every LED display has two connecting pins, are "Anode" and "Cathode", 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 cathode connections of the LED segments are joined together to logic “0” or ground. The individual segments are illuminated by applying a logic “1” or “HIGH” signal via a current limiting resistor to the forward bias the individual anode terminals (a-g).

Seven-segment LED display Common Cathode

 

Common Anode (CA)

In the common anode display, all anode connections of the LED segments are joined together to the logic “1”. To illuminated every individual segment apply 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) which are 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 (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 the microcontroller to drive a 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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