Understanding 7 Segment Displays

7 segment display

What is 7 segment display?

A seven segment display is an electronic device which is used to display alphanumeric digits.

The configuration has an array of 8 LED’s arranged in special pattern to display these digits. Every led is assigned a name from a to h  out of which 7  leds are used to  display numbers and the 8th  led is used for representing the decimal point. 7 segment led  is ten pin package 8 pins corresponds to 8 leds  and the remaining two pins are common which are internally short circuited. The shapes of segments are of hexagonal, rectangular etc.,

7-segment Rectangle and Hexagonal

There are 2 types of configurations used for 7 segment display common Anode display and common Cathode display.

 In common Anode display all the anodes of 8 LED’s are connected in common to the power supply rail(+5v)  and the segment (a to g) which is to be glow is given to ground pin.7 segment anode1

In common cathode display all the cathode terminals are connected to ground  and segment to be displayed is given a supply of 5v.

7 segment cathode1 Generally each LED  are powered separately by using a current source depending upon the intensity of light to be emitted and ratings of LED.

7 Seg

Usually 8 LED’s require a current of 10 to 20mA. To avoid short circuit for led a current limiting resistor is used in series with LED.

Working of 7 Segment Display:

BCD 7 Segment decoder for using this display.This decoder will take input as a binary number of each decimal digit which is known as BCD (Binary Coded Decimal) and give the output as required bit pattern.