Segmental displays are electronic display devices that display alphanumeric characters and numbers using seven LED or LCD segments arranged in a rectangular form. The seven segments are named a to g. 7-segment displays are commonly used in digital clocks and meters. Dot matrix displays use a matrix of LED indicators arranged in a rectangular grid that can be independently turned on and off to display text, numbers or graphics. A 5x7 matrix is most commonly used, with 35 LEDs arranged in 7 rows and 5 columns, allowing individual LEDs to be addressed to display characters.

1. BIE-601
Electronic Instrumentation-II
Unit-4
Display Devices & Recorders
Lecture-2
Mohd. Umar Rehman
umar.ee.amu@gmail.com
16. 4. 2020
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2. Segmental Displays
It is a form of electronic display device for displaying alphanu-
meric characters, decimal numbers i. e. an alternative to more
complex dot-matrix displays.
The most common form of segmental displays are the 7-segment
displays that are widely used in digital clocks, electronic meters,
and other electronic devices for displaying numerical information.
As the name indicates, it is composed of seven segments (LED/LCD
etc.) that are arranged in a rectangular form with 4 vertical seg-
ments and 3 horizontal segments.
The segments are named as a to g.
LED based 7-segment display can have two configurations:
(i) Common Anode configuration
(ii) Common Cathode configuration
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3. Contd...
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4. Contd...
In the common anode configuration as shown above, all the anodes
of the LEDs are connected together to a positive voltage and all
the cathodes are connected to external resistors. The resistors are
necessary to limit the current through the LEDs.
By grounding the external resistors, required digit from 0 to 9 can
be formed and displayed.
e.g. By grounding a, b, d, e, g, the digit 2 can be formed.
By using additional smaller segments, alphabets can also be dis-
played.
In logic terms, common anode configuration connects the anodes
to logic HIGH and cathodes to logic LOW.
Just the reverse happens in common cathode configuration.
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5. Dot Matrix Displays
A dot-matrix display is used to display the information on a ma-
chine, clocks, large panel displays in banks, hospitals, railway sta-
tions.
It is a device of limited resolution. It consists of a matrix of light or
other indicators arranged in a rectangular configuration
This rectangular arrangement is called an array.
By switching ON/OFF the selected LEDs, text numbers or graphics
can be displayed.
A matrix driver or controller converts the instructions from a pro-
cessor into signal that turn ON/OFF the LEDs in the matrix so as to
obtain the required display.
Most commonly used matrix is the 5 × 7 matrix.
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6. Matrix
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7. Matrix
Figure: What I Think
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8. Matrix
Figure: What I Think Figure: What it is actually
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9. Matrix
Figure: What I Think Figure: What it is actually
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10. 5 × 7 Matrix

11. 5 × 7 Matrix...Contd
The above figure shows the common cathode connection of a
5 × 7 matrix
It consists of 35 LEDs placed in 7 rows and 5 columns.
The cathodes of the LEDs in one row are connected together,
similarly the anodes in the column are connected together.
In this arrangement, the anodes are switched to turn ON/OFF the
LEDs.
Several such matrix units can be placed next to each other to form
a large panel to display a string of characters.
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12. 5 × 7 Matrix...Contd