DISPLAY DEVICES AND

PRINTERS

DISPLAY DEVICESDEFINATION:- A display devices is a device for visual or

tactile presentation of images (including text)acquired, Stored or transmitted in various forms. EX : Computer Monitor, TV Screen.

Also know as an information display

MONITOR TECHNOLOGIES

CATHODE RAY TUBE (CRT) LIQUID CRYSTAL DISPLAY (LCD) PLASMA DISPLAY PANEL (PDP) ORGANIC LIGHT EMITTING DIODE

(OLED)

RELATED TERMINOLOGIES

Pixel Resolution Display Size Viewing Angle Response time Brightness

PIXEL

Picture Element

It is the smallest element forming an image

RESOLUTION

No. of pixels per unit video display

Video Graphics Array (VGA)a) 720x400 pixels down in text modeb) 640x480 pixels down in graphics mode

DISPLAY SIZE

Measured as distance from one corner to the

diagonally oppositecorner

Usually measured in INCHES.

VIEWING ANGLE It is angle from which the screen

can be seen from side It is larger for CRT as compared to

LCD

RESPONSE TIME

The minimum time necessary to

change a pixel’s color or brightness

BRIGHTNESS

The amount of light emitted from

the display ( more specifically

known as luminance)

CRT MONITORcathode-ray tube

CRT : Principle

CRT display works on : Electron emission

Electrons are emitted from the Cathode tube

Phosphorescence It is the emission of visible light, when

electron beam strikes phosphor material.

CRT : WORKING Cathode Grid Focusing anode Accelerating anode Aquatic coating

1. Electron guns2. Electron beams3. Focusing coils4. Deflection coils5. Anode connection6. Mask for separating beams for red, green, and blue part

of displayed image7. Phosphor layer with red, green, and blue zones8. Close-up of the phosphor-coated inner side of the

screen

CRT DISPLAY : ADVANTAGES

Offers greater resolution

Widest viewing angle

It is cheap as compared to LCD,PLASMA display

Thickness is much larger. Cannot be used for smaller display,

like watches. View area is less than the offered

monitor size. It is more heavier.

CRT DISPLAY : DIS ADVANTAGES

LCD : Liquid Crystal Display

LCD : DEFINITION

A Liquid Crystal Display is a thin, flat

display device made up of any number

of pixels arrayed in front of a light

source or reflector. It uses very small

amounts of electric power, and is

suitable for use in battery-powered

electronic devices

LCD : WORKING

When electric current

was passed through the

LCD panel the liquid

crystals are aligned with

the first polarized glass

encountered and will

make 90 degree twist

when approaching the

other polarized glass at

the end

When this happens the light from the fluorescent backlight is able to pass through and thus giving us a lighted pixel on the monitor.

When there is no electric current the liquid crystals will not twist and thus the light will not pass through and a black pixel will be shown.

The reason we see the colored images are due to the color filter light passes through the filtered cells creates the colors.

LCD : WORKING

LCD : ADVANTAGES

Brightness Produces very bright images due to high peak intensity. Very suitable

for environments that are brightly lit .

Power Consumption Energy efficient. Consume less than 1/3 the power of a comparable

CRT. Consume less electricity than a CRT and produce little heat.

Physical Aspects Take up about 40% less desk space. LCDs are thin and compact.

Screen Shape Completely flat screen.

Sharpness At the native resolution, the image is perfectly sharp. Adjustments are

required at all other resolutions which can result in measurable degradation to the image.

Aspect Ratio The aspect ratio and resolution are fixed.

Contrast Lower contrast than CRTs due to a poor black-level.

Color and Gray-Scale Accuracy Color saturation is reduced at low intensity levels due to a poor black-

level. Images are satisfactory, but not accurate due to problems with black-level, gray-scale and Gamma.

Cost Considerably more expensive purchase price than comparable CRTs .

Resolution Works best at the native resolution. The native resolution can not be

changed. All other resolutions require adjusting procedures which can cause considerable deterioration of the image.

Viewing Angle Restricted viewing angles. Viewing angles affect the brightness, contrast

and colors shown. Wide angles can lead to contrast and color reversal.

LCD : DISADVANTAGES

PLASMA TECHNOLOGY

PLASMA : DEFINITION

A plasma display panel(PDP) is essentially a collection of very small fluorescent-type lamps, each a few tenths of a millimeter in size

The plasma display itself is a simple device consisting of two parallel glass plates separated by a precise spacing of some tenths of a millimeter and sealed around edges

PLASMA DISPLAY : WORKING

Plasma Display Advantages

Slim profileCan be wall mountedLess bulky than rear-projection

televisionsProduces deep blacks allowing for

superior contrast ratioWider viewing angles than those of

LCD; images do not suffer from degradation at high angles unlike LCDs

Plasma Display Disadvantages

Heavier screen-door effect when compared to LCD or OLED based TVs

Susceptible to screen burn-in and image retention, although most recent models have pixel orbiter

Phosphors lose luminosity over time, resulting in gradual decline of absolute image brightness newer models are less susceptible to this, having lifespan exceeding 100,000 hours, far longer than older CRT technology

Generally do not come in smaller sizes than 37 inches For those who wish to listen to AM radio, or are

Amateur Radio operators Hams or Shortwave Listeners SWL, the Radio Frequency Interference RFI from these devices can be irritating or disabling.

ORGANIC LIGHT EMITTING DIODE(OLED )

OLEDs : PRINCIPLE

OLEDs are special because they are made-up of organic polymer molecules (otherwise known as plastic) allowing light to emit when a voltage is applied

OLEDs : WORKING

Voltage is applied across the OLED device allowing electron to travel from the cathode through the emissive layer to make positively charged electron holes in the conductive layer where the anode draws those electrons.

Quite simple, the anode is drawing electrons through the emissive layer to provide positive electron holes in the conductive layer

Then the positive holes and the electrons collide and recombine which leads to a drop in the electron energy level as visible light radiations is emitted

OLEDs : ADVANTAGES

They have the potential to be able to be produced much more cheaply than conventional LED’s, LCD’s and plasma televisions using processes derived from ink-jet printing

Improved range of colors and brightness's compared to LCD and plasma displays

Potentially very energy efficient They can be deposited on large substrates enabling

large areas to be illuminated Lighter than LED’s Flexible Can produce a true black and infinite contrast ratios

PRINTERS

PRINTER : DEFINATION

In computing, a printer is a peripheral which produces a hard copy (permanent readable text and /or graphics) of documents stored in electronic form, usually an physical print media such as paper or transparencies

PRINTER : TYPES

Dot matrix printer

Inkjet printer

Laser printer

DOT MATRIX PRINTER

DOT MATRIX PRINTER : WORKING

The printer head is made up of a row of pins –

usually 9 or 25 pins forming a vertical bar. To form a

letter, the pins are “fired "in quick succession to

press the ribbon against the paper.

DOT MATRIX PRINTER : ADVANTAGES

low purchase cost.

can handle multipart forms.

cheap to operate, just new ribbons.

rugged and low repair cost.

DOT MATRIX PRINTER : DISADVANTAGES

noisy.

low resolution. You can see the dots

making up each character.

Not all can do colour.

Colour looks faded and streaky.

INKJET PRINTER

INKJET PRINTER : WORKING

INKJET PRINTER : WORKING

The Inkjet Printer is a common type of printer which works by spraying a tiny drop of ink at paper. The technology is probably best explained by this animated picture.

The printing works the same way as the dot-matrix print head above. the only difference is that we are now using droplets of ink instated of hammers.

Inkjet works by having a print catridge with a series of tiny electrically-heated chambers constructed by photolithography

When the bubble, surplus ink is sucked back up from the printing surface. the ink’s surface tension pumps another charge of ink into the chamber through a narrow channel attached to an ink reservoir

LASER PRINTER

LASER PRINTER : WORKING

Images are produced on a drum

A laser beam sets electrical charge on dots on the drum

Magnetically charged power called toner flies to the electrified dots on the drum

The drum rolls the toner on the paper

A second drum burns the toner on the paper

LASER PRINTER : WORKING

The final stage is for the paper to pass through very hot “rollers "which “melt "the ink on the paper

The heat “seals” the ink on to the paper instantly making sure that you do not get smudging or crinkling as you can with other printer types

Q&A

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