Page 54 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Seven segment displays
Seven segment displays are the output display devices that provide a way to display information in the form of
image or text. For displaying the images or text in a proper manner, some types of displays can show only alpha-
numeric characters and digits. But, some displays can also show characters and images. Most commonly used
displays along with the microcontrollers are LCD, LEDs and seven segment displays, etc.

The seven segment display is the most common display device used in many gadgets, and electronic appliances
like digital meters, digital clocks, microwave oven and electric stove, etc. These displays consist of seven segments
of light emitting diodes (LEDs) and that is assembled into a structure like numeral 8. Actually seven segment
displays contain about 8-segments wherein an extra 8th segment is used to display dot. This segment is useful
while displaying non integer number. Seven segments are indicated as A-G and the eighth segment is indicated
as H. These segments are arranged in the form of 8 which is shown in the seven segment display circuit diagram.
A seven segment displays are generally available in ten pin package. In that 8 pins relate to the 8 LEDs, the re-
maining pins at middle are internally shorted. These segments come in two outlines they are common cathode
and common anode. In common cathode configuration, the negative terminals are connected to the common pins
and the common is connected to the ground. When the corresponding pin is given high,then particular LED glows.
In a common anode arrangement, the common pin is given to a logic high and the pins of the LED are given low
to display a number.
Seven Segment Display Working
When the power is given to all the segments, then the number 8 will be displayed. If you disconnect the power for
segment G (that means 7) then that will result number 0. The circuit of the seven segment display is designed in
such a way that the voltage at different pins can be applied at the same time. In the same way, you can form the
combinations to display numerals from 0 to 9. Practically, seven segment displays are available with two structures,
both the type of displays consists of 10 pins.
The numeric seven segment displays can also display other characters. But generally A-G and L, T, O, S and oth-
ers are also available. Some problems may occur with the H, X, 2, and Z. Anyways the common seven segment
display is numeric only. Alphanumeric displays are also available but cost is little more. These types of displays still
have a real purpose due to its high illumination and 7 segment displays are used in dark areas like railway stations.
Even 7 segment display based countdown display is used in NASA, which can be read easily even in sunlight.

Types of 7-Segment Displays
There are two types of seven segment displays available in the market. According to the type of application, these
displays can be used. The two configurations of seven segment displays are discussed below.

• Common Anode Display
• Common Cathode Display
Common Cathode 7-segment Display
In this type of display, all the cathode connections of the LED segments are connected together to logic 0 or
ground. The separate segments are lightened by applying the logic 1 or HIGH signal through a current limiting
resistor to forward bias the individual anode terminals a to g.

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CITS : E & H - Electronics Mechanic - Lesson 9 - 29