How Seven segment display works?

Seven segment display (SSD) - Tutorial:

One of the most common applications of LED is Seven Segment Display. In this short post let us see How Seven segment display works?

We have seen the 7-segment display in our day-to-day life ( ex: basic calculator, digital clock, energy meter displays).

The following figure shows the front of a seven segment display.

  • The LEDs are grouped to form 7 segment display.
  • The seven segment display contains seven LEDs (A, B, C, D,E, F and G) shaped in the figure of 8.
  • In this the LEDs A, B, C, D, E and F are arranged clockwise from the top with LED G in the middle.
  • Each LED is referred as a segment, because it forms part of the character being displayed.

The following figure shows the actual circuit of the seven segment display. The resistors (called as current limiting resistors) are connected in series with the LEDs to protect them against excessive current flow.


  • If a particular LED is forward biased, that LED will glow and produces a bar of light.
  • Out of seven LEDs, by forward biasing various combinations of LEDs, it is possible to display any number from 0 to 9.
  • For example, to display zero, we have to turn on all the segments (LEDs) A, B, C, D, E, F except G.
  • The following table shows segments to be forward biased to get the number.
Number LEDs to be turned ON
1 B, C
2 A, B, G, E, D
3 A, B, G, C, D
4 F, G, B, C
5 A, F, G, C, D
6 F, G, E, D, C
7 A, B, C
9 A, B, C, F, G

In this circuit, the anode terminals or all seven LEDs are connected to the common supply (ie, positive voltage source of +5V). This arrangement is called as common anode type.

In order to glow a particular LED, we have to forward bias that particular LED. For example to glow LED –A, we have to ground the point A and thus the LED becomes forward biased and thus glow. 

We can build 7 segment display in common cathode type too (where all cathode terminals are connected together).

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