## Pages

### Seven Segment Display:

A  display  consisting  of  seven  LEDs  arranged  in  seven  segments  is  called  seven segment   display.   It   is   shown   in   the   Fig.   The   seven   LEDs   are   arranged   in   a rectangular  fashion  and  are  labeled  A  through  G.  Each  LED  is  called  a  segment because it forms a part of the digit being displayed. An additional LED is used for the  indication of a decimal point (DP).

By forward biasing different LEDs we can display the digits 0 through 9. For example,   to display a zero, the LEDs A, B, C, D, E and F are forward biased. To light up a 5,
we need to forward bias segments A, F, C, C, D. Thus in a seven segment display depending  upon  the  digit  to  be  displayed,  the  particular  set  of  LEDs  is  forward biased. The various digits from 0 to 9 which can be displayed using seven segment display are shown in the Fig.

Types of Seven Segment Display

The two types of seven segment display are available called,

1) Common anode type

2) Common cathode type

Common Anode Type

In this type, all anodes of LEDs are connected together and common point is
connected  to  +  V  which  is  positive  supply  voltage.  A  current  limiting  resistor  is required i be connected between each LED and ground.

Common Cathode Type

In this type, all cathodes of LEDs are connected together and common point
is  connected  to  the  ground.  A  current  limiting  resistor  is  connected  between  each LED  and  the  supply  +  Vcc.  The  anodes  of  the  respective  segments  are  to  be connected to + for the required operation of LEDs.

LED Driver Circuit

The output of a digital circuit is logical i.e. either 0 or 1. The ‘0’ means low
while 1’ means high. In the high state the output voltage is nearly 5V while in low
state,  it  is  almost  OV.  If  LED  is  to  be  driven  by  such  digital  circuit,  it  can  be connected as shown in the Fig. 4.21. When output of digital circuit is high, both ends
of  LED  are at  5V  and  it  can  not  be  forward  biased  hence  will not  give  light. While when  output  of  digital  circuit  is  low,  then  high  current  will  flow  through  LED  as  it becomes forward biased, and it will give light.