WORKING OF INPUT DEVICESINPUT DEVICES : is any hardware that takes input from the user.

TYPES OF INPUT DEVICES

Keyboard Optical Mouse Trackball Joystick Light Pen Touch Screen Scanner Digital Camera

KEYBOARD: enters data into computer by pressing one key at a time.

STRUCTURE

Alphanumeric Keys : (A-Z),(0-9),(+,-,*,/) Numeric Keypad : (0-9) on right hand side Function Keys : F1 – F12 Cursor Movement Keys : , , ,

WORKING

When user press a key on keyboard, a tiny computer chip called Keyboard Controller, records that a key has been pressed.

Keyboard Controller places the code into a part of memory, called Keyboard Buffer, indicating the key has been pressed.

This code is called Key’s Scan Code.

Keyboard

Keyboard Controller

Keyboard Buffer

System Software

CPU

Then keyboard sends an Interrupt request (special message to computer system in form of signals) to the system software when it receives a complete key stroke.

When system software receives an interrupt request, it evaluates the request to determine an appropriate response.

It passes the scan code to CPU then.

ADVANTAGE

Faster in entering data than in positioning devices. More reliable and produce fewer error than others.

DISADVANTAGE

Take a lot of time in practice to type quickly. Typing speed is still very slow when compared with computer speed.

MOUSE

Pointing device that translates the motion of mouse into signals.

MECHANICAL MOUSE

Two rollers are placed attached to the mouse ball exactly at 90 degree to each other.

When mouse ball rotates, rollers also rotate. On either side, there is an infrared emitter

and on board chip read pulses (signal) from infrared sensors turns them into binary data.

DRAWBACK

Performance Degradation like ball takes dust and obstructs proper motion of shafts.

OPTICAL MOUSE

It uses small camera that takes 1500 pictures every second.

Light Emitting diode (LED) bounces off light of surface onto Complementary Metal Oxide Semiconductor (CMOS) Sensor.

CMOS sends each picture to digital to see how the image has changed since previous change.

The Digital Signal Processor operates at 18 million instructions per second.

By analyzing these images, processor determines the movement of cursor on screen.

ADVANTAGES

User friendly for computer beginner. Easy and convenient to use GUI. Selection and movement on screen is faster than using keyboard.

DISADVANTAGE

Not easy and convenient to input text. Issuing command is slower than keyboard. Needs practice. Requires flat screen to operate.

TRACKBALL

A pointing device that works similar to mouse.

STRUCTURE

Ball placed in base of mechanical mouse, is placed on top along with two buttons.

WORKING

To move graphic cursor on screen, only ball of trackball is to be moved, not the whole device.

VARIOUS SHAPES

A ball A button A square

ADVANTAGE

Good for limited desk space as user doesn’t have to move entire device.

DISADVANTAGE

It usually not as accurate as mouse. Ball mechanism of trackball also requires more frequent cleaning than a mouse.

LIGHT PEN

It is handheld input device that contains a light source or can detect light.

STRUCTURE

WORKING

Light Pen contains a lens that focuses light from computer monitor onto photoelectric cell.

As monitor’s electron beam passes through lens, cells emit an electric pulses. Strengthen by an amplifier, pulse is sent as digital signal and computer determine

location of pen on screen. A touch of light pen’s control button tells computer to note this position for selection.

ADVANTAGE

More direct and precise than mouse. Convenient for application with limited desktop space.

DISADVANTAGE

It requires special designed monitors.

TOUCH SCREEN

A monitor that has a touch sensitive panel on screen.

STRUCTURE

You interact with the computer by touching areas of screen with fingers that acts as input device.

WORKING

Whenever user touches the screen, it disturbs the electrons emitted on screen and computer processor recognizes the area where the electron are being damaged and considers it as selection.

EXAMPLE

Kiosks, located in stores, hotels, airports and museums.

ADVANTAGE

No extra peripherals are needed except monitor. It allows easy access o commands.

DISADVANTAGE

It is not suitable for inputting a large amount of data. Only items already on screen can be detected.

SCANNER

An input device which translates paper document into an electronic format, which can be stored in computer. The input document can be text, picture, graphics.

TYPES

FLATBED SCANNER

Like a copy machine, this consists of a box having a glass plate on the top, and a lid that cover the glass plate.

WORKING

The document is to be scanned is placed upside down on glass plate. Light source below plate moves horizontally from left to right. After scanning one lne, light beam moves up a little and scan next line and process repeates for all lines.

HANDHELD SCANNER

It has set of LEDs placed in a small case, which conveniently held in hand during operation.

WORKING

To scan a document, a scanner is slowly dragged very steadily and carefully over document.

DIGITAL CAMERA

It allows you to take pictures and store photographed images digitally.

STRUCTURE

WORKING

It uses magnetic or semiconductor technologies to store pictures in binary form.

These pictures can easily be transferred to computer and after transferring camera gets ready for the next picture.

The no. of photographs a camera can click depends upon the memory card of camera which can be easily enhanced by adding a memory slot to it.

Web Cameras can directly be connected to the computers where after clicking picture it gets saved in computer directly.

It is also useful in video conferencing.

ADVANTAGE

It saves money for buying films and developing costs in long term. Images can be reviewed and edited. Unwanted images can be deleted from the memory. Photographic Images can be directly digitized without using scanner. Best for 3-D objects.

DISADVANTAGE

Normally, these are more expensive than ordinary cameras. Photo Printing cost is higher than ordinary cameras.

WORKING OF OUTPUT DEVICESOUTPUT DEVICES: is any hardware component that can convey information to user.

TYPES OF OUTPUT DEVICES

• Monitors

• Printers

• Plotters

• Speakers

• Projectors

MONITORS

• It’s the most important output device

• 2 common types

– CRT

– LCD

• Featured by:

– Refresh rate

– Resolution

– Visible screen size

– Response time

CRT MONITORS

PIXEL:

CRT monitors a CRT is used as the picture of monitor. The screen is divided into rows and columns. Each cell of this screen is called Pixel.

• This vacuum tube contains a negatively charged cathode which shoots electrons at the back of positively charged screen.

• The screen is coated with phosphorous chemical.

• When the electrons strike the back of the screen, phosphorous is excited and it provides a glow to individual pixels.

• The distance between these pixels called as Dot Pitch and it is measured in millimeters.

• The picture tube redraws the picture after a short interval. The number of times the electronic gun redraws the picture on screen is called as the Refresh Rate and it is measured in Hertz(Hz).

• The number of pixels per unit area of the screen is called as Resolution. More the resolution, more clearer will be the picture.

ADVANTAGES OF CRT

• Higher refresh rates.

• Ability to adjust images.

• Display full motion video better.

• Significantly lower cost because the technology has matured.

• Work better at multiple resolutions.

• Modern version may include a sleep mode for energy efficiency.

• Color fidelity, so essential for graphic artist, has not been matched by LCD’s.

• Screen images viewed from side angle are as good as when viewed straight on.

DISADVANTAGES OF CRT

• Larger size takes up more desk space, the bigger the screen, the bigger the foot print.

• Heavy weight.

• Heavier size limits easy and convenient movement.

• Expands more energy and throws off heat.

DVST

DVST behaves like a CRT with an extremely long persistence. A line written on the screen will be visible for up to an hour before it fades away from sight. It is an alternate method for maintaining the screen image which stores the picture definition inside the CRT instead of refreshing the screen.

WORKING

DVST resembles the CRT, it uses the same e-gun and phosphorus coated screen. It also has two guns

PRIMARY GUN:

It is used to store the picture pattern. It draws the picture by knocking out electrons from the storage grid producing a positive charged pattern.

FLOOD GUN:

It is used to maintain the picture display wire grid just behind the screen.

DISADVANTAGES

• Picture erasing is not easy incase of DVST as storage charge removal is very difficult.

• It is not capable of being used in dynamic graphic applications.

• It might lead to degraded picture quality as background glow accumulated.

• On DVST only a single level of intensity can be displayed and only green phosphorus tube are available.

TYPES OF FLAT PANEL DISPLAY

PLASMA PANELS

WHAT IS PLASMA?

Plasma is often called as forth state of matter other three being solid,liquid,gas.

Plasma is a distinct state of matter containing number of charged particle.

CONSTRUCTION

• Plasma panels are two edge-sealed layers of glass separated by a thin layer of neon based gas.

• There are horizontal conductors on one glass layer and vertical on the other glass layer.

WORKING

• When the voltage is applied on the intersection of horizontal and vertical pair of conduction the gas at the intersection become ionized and emit a spot light.

FLAT PANEL DISPLAYS

EMISSIVE

PLASMA PANELS LED PANELS

NON-EMISSIVE

LCD

• All the conductor may have sustaining voltage applied to them that keeps the spot eliminated for several thousand times a second.

• LED stands for light emitting diodes which are basically used in calculators, retail counters, large digital watches etc.

• The first LED’s that were used deep red in color but other colors are also available now.

• It is a type of emissive device.

• In this a matrix of diodes is arranged to form pixel positions in the display.

• The picture definition is stored in the frame buffer.

• As in scan lines refreshing of a CRT, information is read from the refresh buffer and converted to voltage levels that are applied to the diodes to produce light patterns on the display.

• The screen used in computer devices is the LCD screen. The LCD screen produces images by aligning molecular crystals.

• The LCD screen consists of twisted crystals. These crystals are present in twisted form like a spring and they untwist at varying angles when varying voltages are applied.

• These crystals are packed in two screens. The front screen is transparent and back screen is reflective.

• The back screen reflects light towards the front screen. The light gets deviated by these molecules.

• This backed and deviated light produces images on front layer.

ADVANTAGES OF LCD

• Light weight.

• Smaller foot print on desk leaving, freeing up work area on the user desk.

• Flicker free screen.

• More usable display area than on comparably sized CRTs.

• Low frequency radiation is practically eliminated.

• Easy adjustment storage and movement.

• Efficient energy and they do not generate heat.

• Good for basic web surfing.

• Potentially less eyestrain due to reduced screen glare.

DISADVANTAGES OF LCD

• Fragile screen may result in both screen and back light lamp damage if touched. Thus not recommended in environments where it may be handled roughly

• Contrast ratio causes darkness to not be displayed true. Darkest area may be viewed as dark grey rather than black

• Designed only for optimum resolution, can’t adjust images

• The color accuracy of an LCD monitor does not match that of a CRT monitors.

• These are more expensive than CRTs.

PRINTERS

• A printer is an output device that produces text and graphics on a physical medium such as paper.

• Printed information is often called hard copy because the information exists physically and is a more permanent form of output than that presented on a VDU (Monitor). Printers can be grouped into - impact and non-impact printers-

IMPACT PRINTERS

An impact printer forms characters and graphics on a piece of paper by striking a mechanism against an ink ribbon that physically contacts the paper.

NON- IMPACT PRINTERS

• A non-impact printer forms characters and graphics on a piece of paper without actually striking the paper.

SPEED OF PRINTER

The printing speed of a printer is usually expressed in pages per minute (ppm).

RESOLUTION

Printer resolution is often expressed in dpi (dots per inch). The larger the number, the higher the resolution.

ADVANTAGES OF PRINTERS

1. Information produced is permanent.

DISADVANTAGES OF PRINTERS

1. The time to get the printout is slow, when compared with display devices.

2. Paper is wasted for obtaining the output.

3. Printers are generally noisier than display devices.

How it works: The print head travels from side to side across the paper and is made up of numerous pins which are pushed out to form the shape of each character

The pins hit an ink ribbon against the paper so the characters are printed out.

The paper is usually continuous with holes down each side and perforations so the pages can be easily separated by tearing.

Because the pins make an impact against the paper the characters can be printed through several layers of self-carbonating paper to produce duplicate copies.

Speed: Vary from 50 to over 500cps.

Suitable uses: Limited to situations where duplicate copies are needed and the quality is not too important.

Typical uses might be in warehouses where duplicate copies of orders need to produce quickly and cheaply.

Disadvantages The printing quality is low - these printers produce low to medium quality black and white printing and can only print low resolution graphics.

Because of the impact of the pins against the paper, these printers can be quite noisy.

Advantages: The purchase cost is low and the running costs are very low.

They can print fairly quickly, particularly if you remember that multiple copies are being printed in one print run.

They are robust and can operate in harsh environments.

If several sheets of self-carbonating paper are placed into the printer then the impact will produce duplicate copies.

DAISY WHEEL PRINTER

• In this, the print head is like a wheel and the characters embossed at the corner of these arms. It resembles to the petals of daisy flower so it is called a Daisy Wheel Printer.

• A motor spins the wheel at a very fast speed. Daisy Wheel Printer are Serial Impact Printers.

• The output is same as letter quality printing.

SPEED

• These printer have very slow speed of order of 30 to 80 characters per second.

ADVANTAGES

• The final copy looks like it has been typed on high quality typewriter.

• Can print letter quality characters.

• Printing can be performed in either direction, paper can be fed down or up and it has only few moving parts.

DISADVANTAGES

• Printing speed is very slow.

• Cannot print graphics.

• They are very noisy.

• Must need to change the ribbon frequently.

INK-JET PINTER

• An ink-jet printer is a non-impact printer that forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper. Ink-jet printers can produce letter-quality text and graphics in both black-and-white and colors.

• Some ink-jet printers can print photo-quality images on any type of paper. Printer resolution is measured in dots per inch (dpi). The speed of an ink-jet printer is measured in pages per minute (ppm).

HOW IT WORKS:

• The print head contains tiny nozzles through which different colored inks can be sprayed onto the paper to form the characters or the graphic images.

• The ink is forced out by heat or by tiny piezoelectric crystals which change shape when an electric current is applied across them.

SUITABLE USES:

• A popular choice for home use where small amounts of printing are done and photographic quality color printing is needed.

SPEED:

The speed over 150 ppm.

ADVANTAGES OF INK-JET PRINTER

• Inkjet printers are generally quiet.

• Inkjet printers can produce high quality color output.

• These printers are relatively inexpensive

DISADVANTAGES OF INK-JET PRINTER

• Specialized papers are required to produce high quality color output.

• The printing speed is slow compared to a laser printer.

• The ink cartridges and specialized papers are expensive.

• The ink may smear when printed on ordinary paper.

LINE PRINTER

How it works:

Speed:

These print individual pages and work in a similar way to photocopiers.

A drum is charged to match the image and powdered ink (toner) sticks to the surface. The toner is then transferred to the paper and fixed by heat and pressure.

A school or business printer would have a typical speed of 10 to 20 pages per minute (ppm).

10 to 20 ppm.

Suitable uses: Common wherever fast, high quality printing is required.

Disadvantages: Non-color laser printers are more expensive than ink-jet printers (but the difference is narrowing).

Color laser printers are considerably more expensive. (but their speed and high quality output means they are becoming more popular).

Advantages: They are quiet and fast and produce high quality printouts.

Running cost are low because although toner cartridges are expensive to replace, they last a long time.

DRUM PRINTER

This is an impact line printer. It basically consist of a drum which is divided into number of tracks. The total tracks are equal to size of printer that is for the paper width of 132 characters, a drum will have 132 tracks.

• A character set is embossed on the track. The drum in the drum printer is made to rotate at a very fast speed.

• Paper is sandwiched between paper and hammer.

SPEED

• Between 300 to 2000 lines per minute.

ADVANTAGES

• Much quieter.

DISADVANTAGES

• You cannot do multiple forms.

CHAIN PRINTER

These are impact printers because the actual contact is made by chain on one side and

hammer on the other side of ribbon.

WORKING OF CHAIN PRINTERS

• These are called as chain printer because the chains are used for printing the output.

the chain is basically a kind of tape wound on two spools with a character set repeated,

three or four times.

• A character set may have 48,64 or 96 characters embossed on it.

SPEED

400 to 3000 lines per minute.

ADVANTAGES

• It adds flexibility.

• Better printing performance.

• Permits simplified type-changing process.

DISADVANTAGES

• These make a huge amount of noise.

• They can only print one type and size of font and cannot print images.

PLOTTER

How it works: A drum plotter prints by moving a pen sideways over the surface of a sheet of paper.

One high precision motor moves the pen from side to side.

Another high precision motor moves the paper backwards and forwards.

An electromagnet lifts and drops different colored ink pens onto the paper to draw lines.

Suitable uses: Plotters are restricted to line drawing and can only create a solid region of color by drawing a number of close, regular lines.

Plotters are often used in science and engineering applications for drawing building plans, printed circuit boards and machine parts.

Advantages: They are accurate and can produce far larger printouts than standard printers.

SPEAKERS

• These transducers convert an alternating electrical current into sound.

SUITABLE USES

• They can output music as well as the spoken word.

• Useful for blind users where text or figures can be spoken by the computer.

• A speaker and computer-synthesized voice can be used by automated systems to read information such as telephone numbers or traffic updates.

ADVANTAGES

• Cheap and widely available.

• Capable of producing very high quality sound.

DISADVANTAGES

• They are an analogue device so the digital sound signal has to be converted, usually by a sound card.

PROJECTOR

WORKING OF LCD PROJECTOR

• The video projector contains LCD panels. At the center of projector is a halogen bulb which is surrounded by panels.

• The panels produce light. As the halogen bulb heats up the crystal melts and allow more light to pass through. Hence the intensity of halogen bulb brings about the difference in tones.

• Higher the temperature of bulb, lighter the tone and vice-versa.

• Images travel to the tube present inside the projector from DVD player or satellite box.

• These images in turn bounds on a screen that is coated with phosphorous. Every fragment of light hitting the screen is termed as Pixel .

• On hitting the screen, the pixel breaks down into its color components i.e., red, blue, or green.

• The heat produced by halogen, bulb is controlled by voltage that flows into LCD video projector.

ADVANTAGES OF LCD PROJECTORS

• Enable a lot of people to be able to see something even from a distance.

• They also produce sharper images.

• They also have an edge in light efficiency.

• They generate largest possible image size.

• They can be used to throw smaller images a great option also. So it can serve as an inexpensive.

• Low cost.

• Space saving.

• Easy to install.

DISADVANTAGES OF LCD PROJECTORS

• Image quality may not be as good as projected.

• Dark room often required.

• Maintenance required.

• Installation can be more involved.

• Separate audio system required.

• The pixels on the chip can burn out. When one pixel burns out, you wont be able to repair it. You will have to replace the whole chip.