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7-Segment Display

Seven-segment display is a form of electronic display used for displaying alpha-numeric characters. A seven-segment display is a set of seven LEDs elements, arranged to form a figure of 8. Each of the LEDs is turned ON and OFF and the combination of LEDs which are ON forms a character. If all elements are activated, the display shows a numeral 8. Numbers from 0-9 and few alphabets can be displayed.

The working of 7 segment display is on the similar lines as that of and LED as the 7 segment displays is eventually made up of 7 LEDs and an LED for the decimal point. The use of the decimal point is to display decimal numbers like 3.1 or 7.5. The 7 segment display are of two types viz. Common Anode display and Common Cathode display.


Common Anode display

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Common Cathode Display

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Implimentation

All of the cathodes (negative terminals) or all of the anodes (positive terminals) of the segment LEDs are connected and brought out to a common pin; this is referred to as a "common cathode" or "common anode" device. Hence a 7 segment plus decimal point package will only require nine pins. Common cathode implementations require logic low (0) to turn on a segment, common anode implementations require logic high (1) to turn on a segment.


BCD to Seven Segment Conversion

The 7 segment displays are very popularly used in circuit boards and PCBs as display devices. This displays needs active nine pins of micro controller or other logic IC for driving it. And the scenario goes worst if multiple 7 segment displays are used. This makes the circuit bulky with many interconnections. To avoid this, it is essential to use a BCD to 7 segment display driver ICs like IC 7447 and IC 7448 in order to drive the displays. The inputs to the IC are 4 bit BCD value and the outputs are 7 pins which are connection to the 7 segment display.

Pulpit rock


The BCD value chart

BCD Input Data 
 SW3  SW2   SW1  SW0   Numeral Displayed 
00000
00011
00102
00113
01004
01015
01106
01117
10008
10019



Advantages

  • Cost: The cost of the entire module of 7 segment display is very cheap as it only contains LEDs.
  • Efficiency: LED displays in general are extremely efficient.
  • Heat dissipation: The heat dissipated from this displays is very less and that increases the life of the devices.


Disadvantages

  • limited characters: Seven-segment displays are capable to display only numbers from 0-9 and few alphabets.
  • Type of display: The appearance of the two types of display are very similar and that causes difficulty interfacing it with controllers



Applications

  • Digital watches
  • electronic device display
  • timers
  • calculators
  • Car panel displays, etc.



Interfacing 7 Segment Display with Arduino










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