M. Raihan
Email: rianku11@gmail.com

Output Devices
Part-2

Types of LCD
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LCD element form the pixels in LCD screen.
 The LCD elements are switched on and off by different techniques to
display an image on the screen.
 There are two types of LCD screens: passive-matrix and active-matrix.

Passive Matrix LCD
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Each LCD element in placed between two electrodes
and arranged in rows and columns in X-Y matrix
format.
The bottom electrodes of each row elements are
connected together and the top electrodes of each
column elements are connected together.
The elements in a row are controlled by a row-driver
and the elements in a column by a column-driver.
Activating a row-driver and a column driver results in
a current through a specific LCD element.

Passive Matrix LCD (continue)
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 An image is created on the screen by activating a row
driver and activating the column drivers in sequence like
scanning a line.
 The drawback of this simple design is that if a current
through a cell is large, then adjacent elements, often those
in the same column, also get affected and this results in
ghosting.
 If the current through an element is too weak, the
elements don’t switch on and off very quickly which results
in poor contrast and losing detail in moving images.
 The dual scan technique improves the performance.

Active matrix LCD
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AMLCDs use one transistor driver for each LCD element.
The transistors are arranged in the matrix format.
 It allows the current through individual elements to be switched on
and off quickly with sufficient current to get good contrast.
The electrodes for active matrix panels are also made of the
transparent material.
The transistor drivers are fabricated right on the panel substrate,
using thin film technology.
As the transistors are able to switch the elements more rapidly than
the passive matrix scheme and adjacent elements are not affected,
large currents can be used without ghosting.
The higher currents provide higher contrast and sharper and
brighter images.

Techniques for solving
Viewing Angle Problem
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The simplest technique uses a diffusing film on the top layer of the
display.
It causes the light traveling in specific direction to divert in different directions.
In the second technique, instead of passing the current from top
through the liquid crystal to bottom
The electrodes are arranged in such a way that the current flows from side to side.
It causes the molecules to align in horizontal direction, which results in wider viewing
angles.
In the third technique, each liquid crystal element is divided into
multiple regions
The substrate is pre-tilt in different directions so that the molecules align in different
directions.
It causes the light to emerge different directions, which results in wider viewing angles.

Printer
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Printers are the primary output devices used to prepare
permanent documents for human use.
 Printing output is called hard copy output.
There are two types of printers −
Impact Printers
Non-Impact Printers
Three different types of printers are in use today. They are-
Dot-Matrix printer
Ink-Jet printer and
Laser-Jet printer

Impact Printers
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Impact printers print the characters by striking them on
the ribbon, which is then pressed on the paper.
These printers are of two types-
Character printers (Dot Matrix Printer(DMP), Daisy Wheel)
Line printers (Drum Printer, Chain Printer)
Characteristics of Impact Printers-
Very low consumable costs
Very noisy
Useful for bulk printing due to low cost
There is physical contact with the paper to produce an image

Non-impact Printers
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Non-impact printers print the characters without using
the ribbon. These printers print a complete page at a time,
thus they are also called as Page Printers.
These printers are of two types-
Laser Printers
Inkjet Printers
Characteristics of Non-impact Printers-
Faster than impact printers
They are not noisy
High quality

Dot-Matrix Printer
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A dot matrix printer has a printer head, which contains an array
of 7, 9, 14, 18 or 24 pins arranged in a vertical column.
 While printing, the pins forming one column of dot pattern of
the character matrix project from the print head and press the
inked ribbon against a plain paper.
 Only one column of dot pattern of character matrix is printed at
a time.
 As the print head moves across the line, series of vertical dot
patterns representing the character are retrieved from the
printer’s internal memory and printed.

Dot-Matrix Printer (continue)
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Dot-Matrix Printer (continue)
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The print head is mounted on a carriage and
moved back and forth along a rail by a belt.
 The dot-matrix printers receive stream of
character from the computer, convert to series of
column of dot patterns and print.
 The print quality depends on the number of pins
provided on the print head.
 24-pin printers produce high quality printouts.

Ink-Jet Printer
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The operation of the ink-jet printer is similar to that of a
dot-matrix printer.
Ink-jet printers have tiny nozzles on the print head that
spray ionized ink onto a plain paper in the pattern to form
the characters and images.
The print head cartridge has 50 or more nozzles and is
mounted on a carriage that is carried back and forth along
a rail by a belt that is driven by a motor.
The print head is connected to the electronic control unit
through a long, flat, flexible print head cable.

Ink-Jet Printer (continue)
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Ink-Jet Printer (continue)
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 When the PC sends a character to be printed, a series of vertical dot patterns representing
the character is retrieved from the printer’s internal memory and sent through a series of
print nozzle driver circuits.
The driver amplifies the signals into the fast, high-energy pulses needed to fire minute
droplets of ink from each nozzle.
As the pulse reaches the nozzle, it creates an intense surge of heat that literally creates a
bubble.
The nozzle cools down in a fraction of a second and becomes ready for another pulse.
The print quality of ink-jet printer depends on the quality of paper also.
They require periodic maintenance, as they use liquid ink.
The ink may dry in the nozzles and clog them.

Laser-jet printer
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Laser-jet printers function like a plain paper copier.
While a bright light source is used in a plain paper copier
for generating the images, a laser is used in laser printer.
The laser printer creates an electrostatic image of a text or
graphics page on a photosensitive drum using the laser
beam.
When the drum is moved across the toner, it attracts the
toner particles and deposits on the electrostatic image.

Laser-jet printer (continue)
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Laser-jet printer (continue)
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The drum is then pressed against a plain paper to transfer the
image on to the paper.
The paper is then passed between hot rollers to fuse the toner
particles into the paper.
The area of the drum is the same as that of the paper onto which
the image is transferred.
Every point on the drum corresponds to a point on the paper.
Laser printers are very popular today because of their print
quality and relatively low running cost.
 The print quality is less sensitive to paper quality.

Laser-jet printer (continue)
06-Aug-17 20
 Laser printers get all the information about
the page to be printed and keep them in their
internal memory before starting the printing.
 The amount of memory present in a printer
determines its capability.

Daisy Wheel Printer
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Head is lying on a wheel and pins corresponding to characters are like petals
of Daisy (flower) which is why it is called Daisy Wheel Printer.
These printers are generally used for word-processing in offices that require
a few letters to be sent here and there with very nice quality.
Advantages:
More reliable than Dot Matrix Printer (DMP)
Better quality
Fonts of character can be easily changed
Disadvantages:
Slower than DMP
Noisy
More expensive than DMP

Daisy Wheel Printer(continue)
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Line Printers
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The line printer is an impact printer that prints one
entire line of text at a time.
It is mostly associated with unit record equipment and
the early days of digital computing, but the technology is
still in use.
Line printers are of two types −
 Drum Printer
 Chain Printer

Drum Printer
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This printer is like a drum in shape hence it is called drum printer. The
surface of the drum is divided into a number of tracks. Total tracks are equal
to the size of the paper, i.e. for a paper width of 132 characters, drum will have
132 tracks.
Different character sets available in the market are 48 character set, 64 and
96 characters set.
Drum printers are fast in speed and can print 300 to 2000 lines per minute.
Advantages:
Very high speed
Disadvantages:
Very expensive
Characters fonts cannot be changed

Drum Printer (continue)
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Chain Printer
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In this printer, a chain of character sets is used,
hence it is called Chain Printer. A standard
character set may have 48, 64, or 96 characters.
Advantages:
Character fonts can easily be changed.
Different languages can be used with the same printer.
Disadvantages:
Noisy

Chain Printer (continue)
06-Aug-17 27

Thank You
06-Aug-17 28