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Ashis Talukder, MIS, DU. 1 Lecture Output Devices

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Page 1: Lec monitor

Ashis Talukder, MIS, DU. 1

Lecture

Output Devices

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Ashis Talukder, MIS, DU. 2

Output Devices An output device is an electromechanical

device, which accepts data from a computer, and translates them into a form, which is suitable for the use by the outside world (the user).

Most commonly used output devices: Monitors Printers

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Monitors Monitors display the

generated output on a television like screen.

Types of monitors: Cathode Ray Tube (CRT)

monitors

Flat-panel Displays

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Comparing Monitors When comparing monitors, four features have

been considered: Size Resolution Refresh rate Dot pitch

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Comparing Monitors Size

A monitor's size is the diagonal measurement of its face, in inches.

Larger monitors are available, but can be expensive.

For years, 15" monitors (13"viewing

area) were standard.

Today, 17" monitors (15" viewing area) are common.

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Comparing Monitors Resolution

Picture element (Pixel), is the smallest number of phosphor dots that the electron gun inside the monitor can focus on (01M pixel= 01 Million pixels)

In color display, three phosphor dots combine to form a single unit pixel

1 pixel

Resolution is the number of pixels on the screen, expressed as a matrix (such as 800x600).

A 17" monitor offers resolutions from 640x480 up to 1280x1024.

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Comparing Monitors Refresh Rate

Refresh rate is the number of times each second that the electron guns scan the screen's pixels.

Refresh rate is measured in Hertz (Hz), or cycles per second.

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Comparing Monitors Dot Pitch

Dot pitch is the distance between the phosphor dots that make up a single pixel.

In color monitors, three dots (red, green, and blue) comprise each pixel.

Look for a dot pitch no greater than .28 millimeter.

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CRT Monitor

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Organization of CRT Monitors Its main part is a ‘Cathode Ray Tube’. At its one end there is a source of high voltage. There is a ‘magnetic coil/yolk’ ; which is used to

control the flow of electron At the back of the screen there are ‘phosphor

dots’

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Working Principle of CRT Monitors

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Working Principle of CRT Monitors Electron gun shoots

streams of electrons at a high voltage towards the screen

Magnetic coil controls the flow of electrons

Phosphor dots on the back of the screen glow when the electron beam hit them

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Working Principle of CRT Monitors Electron gun do not

scan it randomly but in a designed fashion

The electron gun scans from left to right

Then from top to bottom

Refreshing every phosphor dot in a zigzag pattern

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Why TV is not used as monitor? Television display contains resolution which is

just a half of computer monitor. So it cannot show output of computer

operation. Resolution indicates the sharpness of an image

determined by the number of pixels on the screen.

TV contains only the half number of pixels than monitor, so the resolution

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Advantages of CRT Monitors Response Time

Faster response time. Critical to people who watch videos or play

games on their PC’s. The fastest LCD’s offer a response time of about

25 milliseconds as apposed to CRT’s that have a response time of about 13 milliseconds.

Lower cost Viewing Angle

Very wide

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Disadvantages of CRT Monitors Physical size

Bulky, heavy, use vacuum tube technology, takes more desktop space

Power Consumption and Radiation Emission Consumes more energy Emits harmful radiation. The metal shield behind

the glass of your monitor protects your body from a flood of radiation

It holds a dangerous electrical charge even after turned off and can last up to several years and be hazardous and even deadly to anyone who opens a CRT monitor casing.

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LCD Monitor

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LCD Monitors the pixels are addressed in

rows and columns

The column and row wires attach to transistor switches, one for each pixel.

The one-way current passing characteristic of the transistor prevents the charge applied to the pixel from draining between refreshes to the display image.

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Advantages of LCD Monitors Power Consumption and Radiation Emission

Lower power consumption Doest not emit Radiation Not subject to Electromagnetic Interference

Viewing High Resolution Cause less eyestrain Does not flicker or glare

Physical Size Compact and Lightweight, and hence portable Space saving Can be mounted on a wall or panel

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Disadvantages of LCD Monitors Expensive than CRTs Resolution

LCD monitors can only display information well at the resolution they were designed for. At any other resolution, image quality will suffer.

Lower refresh rate Response Time

It is much slower. The delay can cause a ghosting effect on images it displays.

Viewing Angle Smaller, needed to be viewed more directly from the front. From the side the images on an LCD screen can seem to

disappear, or invert

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Output unit: Speaker Speaker is well known output device usually

outputs sound It is attached with the sound card of the

computer Sound can be controlled by controller Electric signal is converted and it changes the

air pressure outside which we call sound

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Output device: Touch screen

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Output unit: Plotter A output unit like printer used to print large size

posters

Requires specified paper and ink

It takes a few hours to print the poster

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Output unit: Plotter

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Next Class

Memory Unit