Output Peripherals :

n  video display monitors

n  monochrome and color

n  CRT and LCD

n  printers

n  character, line, and page

n  sound and voice output

 Cathode Ray Tube (CRT):                                               

n  The cathode ray tube (CRT) is a vacuum tube containing one or more electron guns (a source of electrons or electron emitter) and a fluorescent screen used to view images. 

n  phosphors are excited by electron gun beams

n  RGB composite color is used

n  Uses horizontal scanning pattern to refresh phosphors

n  It has a means to accelerate and deflect the electron beams onto the screen to create the images. The images may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets or others. CRTs have also been used as memory devices

 Liquid-Crystal Display  (LCD)                     

n  A liquid-crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals. Liquid crystals do not emit light directly.

n  A liquid crystal display (LCD) has liquid crystals between two sheets of material. When an electric current passes through the crystals, they twist, causing some light waves to be blocked and allowing others to pass through, which creates the images.

n  The LCD screen is more energy efficient and can be disposed of more safely than a CRT. Its low electrical power consumption enables it to be used in battery-powered electronic equipment.

Plasma monitor or flat-panel display

•      A gas plasma monitor is a flat-panel display.

•      A gas plasma monitor, substitutes a layer of gas for the liquid crystal material.

•      When voltage is applied, the gas releases ultraviolet light that causes pixels on the screen to glow and form an image. 

Printers :

n  An external hardware device responsible for taking computer data and generating a hard copy of that data. Printers are one of the most commonly used peripherals and they print text and still images on the paper.

Impact Printer

Ø These printers have a mechanism that touches the paper to create an image.

Ø These printers work by banging a print head containing a number of metal pins which strike an inked ribbon placed between the print head  and the paper.

Non-Impact Printers

Ø These printers create an image on the print medium without the use of force.

Ø They don’t touch the paper while creating an image.

Ø Non-impact printers are much quieter than impact printers as they don’t strike or bang a print head .

Daisy Wheel Printer :

Ø A daisywheel printer is an impact  printer that uses a wheel as a print head and consisting of an attached extensions or spokes on which molded metal characters are mounted.

Ø As the wheel rotates, a hammer strikes  the backside of the spoke and presses it

   against  the paper to print a character.

Advantages

•      Can print letter quality characters.

Disadvantages

•      These printers are very noisy as there occur

great movement  during the printing.

•         Printing speed is very slow, i.e. less than 90cps.

•         Cannot print graphics

Dot Matrix Printer    

Ø The term dot matrix refers to the process of placing dots to form an image.

Ø The dot matrix forms images one character at a  time as the print head moves across the paper.

Ø  Uses tiny pins to hit an ink ribbon on the paper much as a typewriter does.

Ø 9 to 24 vertical column pins are contained in a rectangular print head. When print head moves across the paper,  pins are  activated  to form a dotted character image.

Ø These printers can produce carbon copies along with the originals.

Ø Dot Matrix were 1^st introduced by Centronics in 1970.

Advantages:

Ø In-expensive.

Ø can print multipart forms.

Ø Energy efficient.

Ø Dot-matrix printers can withstand dusty environment, vibrations and extreme temperature.

Disadvantages:

Ø Noisy

Ø Low resolution

Ø Limited fonts flexibility

Ø Poor quality graphics output.

Ø Its speed is usually 30 to 550 characters per second (cps).

Line Printer

Ø A line printer is a high-speed impact printer  that prints an entire line at a time.

Ø The speed of a line printer is measured by the number of lines per minute (lpm) it can  print.

Ø Line printers are often used with mainframes, minicomputers, or with a network in application   such as manufacturing, distribution, or shipping.

Ink-Jet Printer

It is a non-impact printer producing a high quality print. Inkjet printers were introduced in the later half of 1980s and are very popular owing to their extra-ordinary performance.

How Inkjet Printer works?

Ø Print head having four ink cartridges moves .

Ø Software instructs where to apply dots of ink, which color and what quantity to use.

Ø Electrical pulses are sent to the resistors behind each nozzle.

Ø Vapor bubbles of ink are formed by resistors and the ink is forced to the paper through nozzles.

Ø A matrix of dots forms characters and pictures.

Inside an Inkjet Printer

·        Print head Assembly:

·        Contains a series of nozzles

·        Ink Cartridge:

·        Depending on the model & manufacturing of printers, ink cartridge come in various combinations.

·         Print head stepper motor:

·        A stepper motor moves the print head assembly back and forth across the paper.

·        Stabilizer bar:

·        The movement of print head is controlled and made precise by a stabilizer bar.

·         Belt:

·        A belt is used to attach print head assembly to the stepper motor.

·        Paper tray/feeder:

·        It enables the user to load the paper into the printer.

·         Rollers:

·        Control the movement of the paper.

·        Control circuitry:

   control all the mechanical aspects of the operation as well as decode the information sent to the printer from the computer.

Advantages:

·        High resolution output of 300 dpi. And more .

·         Energy efficient.

·         Many options to select.

·        Disadvantages:

·         Expensive.

·         Special paper required for higher resolution output.

·         Time consuming in case of graphics printing.

Thermal Printer

n  Thermal printers are in-expensive printers mostly used in fax machines. The  Thermal printers are further classified into two types. They require a special paper.

(1) Electro thermal printers:

(2) Thermal Wax printers:

·        Thermal printers use heated pins and ribbons with different color bands.

·        These printers contain a stick of wax like ink. The ribbon passes in front of a print head that has a series of tiny heated pins. The pins cause the wax to melt and adhere to the paper and when temperature reaches to a certain level, it is hardened.

Laser Printer

·       Laser printers use very advanced technology and produce a high quality output.

·       Laser printers can also produce high quality graphics images.

·       Resolution is 600 to 1200 dpi.

·       Paper is fed and the drum rotates.

·       A laser beam conveys information from the computer to a rotating mirror and thus an image is created on the drum.

·       The charges on the drum are ionized and the toner sticks to the drum.

·       Toner is transferred from drum to paper.

·       Heat is applied to fuse the toner on the paper.

Plotter

·       A large scale printer which is very accurate in producing engineering drawings and architectural blueprints.

·       Two types of plotters are flatbed and drum.

·       Flatbed plotters are horizontally aligned. It generates high-quality documents by moving ink pens over the surface of a page.

·       while drum plotters are vertically positioned

Sound and Voice Output

•      An audio output device produces music, speech, or other sounds.

•      Two commonly used audio output devices are speakers and headsets.

•      Most personal computers have an internal speaker that outputs low-quality sound.

•      Many users add high-quality stereo speakers or purchase PCs with larger speakers built into the sides of the monitor.

•      A woofer can be added to boost low bass sounds.

•      A headset plugged into a port on the sound card allows only the user to hear sound from the computer.