This document discusses seven segment displays and decoders. Seven segment displays use 7 LEDs labeled a-h to display digits 0-9 by turning on different combinations of LEDs. There are two types of displays - common anode and common cathode - depending on how the LEDs are connected. Seven segment decoder ICs like the 7446 and 7448 are used to drive the displays. They convert binary coded decimal (BCD) input to activate the correct LEDs to display a number. The 7446 is for common anode displays and the 7448 is for common cathode displays.

2. SEVEN SEGMENT DECODERS
 Introduction
 A LED emits radiation – forward biased (free electrons recombine
with holes near the junction)
 Free electrons fall from higher energy level to lower energy level ,
give up energy ==== heat or light
 Gallium, arsenic, Phosphorous ==LED emits === red, green,
blue, yellow, orange and Infrared(visible) light
 LED === visible radiation === test instruments & pocket
calculators, etc

3. Seven Segment Indicators
 Seven LEDs === a through h
 By forward biasing Different LEDs
==== display digits 0 to 9
 To display 0
 Light up a, b, c, d, e and f
 To display 5
 Light up a, c, d, f and g
 Two types of Seven Segment Indicators
 Common anode ( all anodes connected
together )
 Common cathode (all cathodes connected
together )
 Resistors size - determines the current ( 1 to 50 mA)
flow through the LED

4. Current limiting resistor
between LED and Ground
Current limiting resistor
between LED and +Vcc

5. Seven segment decoder-driver
• IC decoder === used to drive Seven Segment
Indicators
• Two types depends on
Common anode indicators
 Common cathode indicators
• Each decoder driver has 4 input pins ( ABCD ) &
7 output pins ( a through h )
• Two types :
– IC 7446
– IC 7448

6. IC 7446 Decoder - Driver
• 7446 driving a common-anode
indicator.
• Logic circuits inside the 7446
convert the BCD input to the
required output.
• BCD = 0111, IC 7446 force LEDs
a, b, and c to conduct === digit 7
appear on the seven-segment
indicator.
• current-limiting resistors between
the seven-segment indicator and the
7446 === to limit the current in
each segment === between 1 and 50
mA, (bright display )

7. IC 7448 Decoder - Driver
• 7448 drives a common-cathode
indicator.
• Logic circuits inside the 7448
convert the BCD input to the
required output.
• BCD = 0100, IC 7448 force LEDs
b, c, f and g to conduct === digit 4
appear on the seven-segment
indicator.
• it has own current-limiting resistors