7 Segment Display

A 7 segment display is typically used to display numbers from 0-9. It consists of 7 bar segments and a dot( 8 Segments).

Segments are numbered A to F and DP for the dot or decimal place. There are 2 types of 7 Segment display

–> Common Anode

–> Common Cathode

A common Anode display has common pin that is connected to Vcc. Each segment is connected through resistor( current limiting) to the ground. To shutoff the segment we need to connect to Vcc.

Driving a 7 Segment Display

A 7-segment display can be thought of as a single display, but it is actually seven individual LEDs within a single package and as such these LEDs need protection from over current. LEDs produce light only when it is forward biased with amount of light emitted being proportional to the forward current.

The forward voltage drop across a red LED segment is very low at about 2 volts, so to illuminate correctly, the LED segments should be connected to a voltage source in excess of this forward voltage value with a series resistance used to limit the forward current to a desirable value.

Typically for a standard red colour 7-segment display, each LED segment can draw about 15 mA to illuminated correctly, so on a 5 volt digital logic circuit, the value of the current limiting resistor would be about 200Ω (5v – 2v)/15mA, or 220Ω to the nearest higher preferred value.

Schematic Diagram

7 Segment Display
7 Segment Schematic

Common cathode is opposite to common anode. Common pins are connected to ground. To light up each segment is set to HIGH.

7 Segment display table.

Band ColourBand #1Band #2Band #3Multiplier value for
Band #3
Band #4
Black
0001
Brown11110
Red222100
Orange3331000
Yellow44410000
Green555100000
Blue6661000000
Violet77710000000
Gray888100000000
White9991000000000
None20%
Silver10%
Gold5%

 

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