Input Output Media

Working principles of keyboard, Mouse & Printer

 Computer Keyboard Functions: How does a Keyboard Work?

• A computer keyboard is a hardware device that functions in accordance

to the instructions made by the user.
• It comprises circuits, switches and processors that help in transferring
keystroke messages to the computer.

Functioning of a Keyboard:
In general, there are 80-110 keys in a computer keyboard. The keys may vary
depending upon the brand and the type of operating system. Nevertheless,
the shape, size and spacing of keys are almost same for all keyboards. Also
the layout or arrangement of keys that represent letters, signs and symbols is
same, which is referred to as QWERTY.

• The working of a computer keyboard can be compared to a miniature

computer.
• Inside the keyboard, there are metallic plate, circuit board (key matrix)
and processor, which are responsible for transferring information from the
keyboard to the computer.
• Depending upon the working principle, there are two main types of keys,
namely, capacitive and hard-contact.
Capacitive Key
On the underside of a capacitive key, a metal plunger is fixed, which helps
in activating the circuit flow. When a capacitive key is pressed, the metal
plunger applies a gentle pressure to the circuit board. The pressure is
identified by the computer and the circuit flow is initiated, resulting in the
transfer of information from the circuit to the currently installed software.
Hard Contact Key
• A hard contact key is attached with a metallic plate that helps in
connecting the circuit board. When the hard contact key is pressed, it
pushes a metallic plate, which in turn touches the metallic portion of the
circuit plate. This overall process of completing a circuit results in a circuit
flow, allowing the transfer of the message to the central processing unit
(CPU), which is further transmitted to the software.
• keyboard is a series of switches connected to a small keyboard
microprocessor that monitors the state of each switch and initiates a
specific response to a change in state.
• When the user presses a key, it causes a change in the amount of current
flowing through the circuit associated specifically with that key.
• The keyboard microprocessor detects this change in circuit flow.
• By doing so, a microprocessor can tell when a key has been presses and
when it is being released.
• Depending upon which key’s circuit carries a signal to the
microprocessor, the processor generates the associative code, also known
as “scan code” and send it to the operating system.
• A copy of the code is also stored in the keyboard’s memory.
• When the operating system reads the scan code, it informs the same to the
keyboard and the scan code stored in keyboard’s memory is then erased.

Working principles of mouse

What is a mouse?
The mouse is a pointing device which helps us to operate the computer.
Unlike the complicated hardwares such as Mother board, RAM, Hard disk,
Processor of the computer, the mouse is designed with a simple circuit to
process. Now a days, we get varieties of mouse with different technologies
in the market.
The developing applications in the computer field has not completely
excluded the mouse yet. Although, we have switched to Touchpads in
Laptops, "the function of mouse is easy and user-friendly when compared
with touch pads for a new user", says the users. Mostly all the applications
are operated with mouse for easy working. In recent days, the optical mouse
had overcome the old ball mouse, because of its 'easy to use' function.

Disadvantages of Ball mouse

With the previous ball-rolled mouses, the movement of the pointer in the
computer is decided by the ball inside the mouse. So, if the ball gets
damaged, or if dust gets clustered, the operation of the mouse becomes
problem. When dust gathers, it takes some time to clear it too. With these
disadvantages, the ball mouse was slowly moved away form the computer
technology leaving the optical mouse to fill its space.

Working of Optical mouse:

Now, almost everyone tries to switch from ball/roller mouse to Optical
mouse. As the cost of the mouse is also being decreasing, the replacement is
quiet quicker. To connect this optical mouse, the necessity is PS/2 or USB
plug, and windows, Macintosh or LINUX operating system installed in the
computer.

The main components of the optical mouse are:

• Inbuilt optical sensor
• High speed camera which can take 1000 pictures at a time
• LED

• These optical mouses do have an inbuilt optical sensor.

o The optical sensor reads the movements of the optical mouse (moved by
the user) with the help of the light rays which comes out from the bottom.
( The area in which a light glows).
• When the user moves the optical mouse, the LED (Light Emitting Diode)
present inside the mouse emits the light according the minute movements.
• These movements are send to the camera as light rays.
• The camera captures the difference in light rays as images.
• When the camera captures the images, each and every pictures are
compared to one another with the digital technology.
• With the comparison, the speed of the mouse and the direction of the
movement of the mouse are rapidly calculated.
• According to the calculation, the pointer moves on the screen.

Comparison between a roller/ball mouse and optical mouse 

• The optical mouse does not have any movable parts as of the ball mouse
So, the life of the optical mouse is long compared to the ordinary mouse.
• Since the mouse works with the sensor recognition, the movements are
clearly captured and so the moves gives out a same function in all moves.
• Since the ball is absent in the optical mouse, the weight of the optical
mouse is less than that of the ball mouse.
• The dust clustering problem is abolished in the optical mouse as its parts
are all static.
• The optical mouse can also function good without a mouse pad, which is
impossible with ordinary mouses. Any way, optical mouses cannot be
used above reflecting glasses or any glass materials.

Working Principles of Scanner 

Introduction & overview of scanner
Flatbed scanners, also called: desktop scanners, are the most versatile and
commonly used scanners. In fact, this article will focus on the technology as
it relates to flatbed scanners.

Sheet-fed scanners are similar to flatbed scanners except the document is

moved and the scan head is immobile. A sheet-fed scanner looks a lot like a
small portable printer.

Handheld scanners use the same basic technology as a flatbed scanner, but
rely on the user to move them instead of a motorized belt. This type of
scanner typically does not provide good image quality. However, it can be
useful for quickly capturing text.

Printer
its types, working and usefulness
 Inkjet

Impact
Thermal
Printer

Leser
printer

Daisywhel
Non-Impact
Printers
Dot-Matric

What is a printer?
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.

“Factors affecting print quality”

DPI: It is a measurement of printer’s resolution indicating how many ink

dots can be placed by the printer in one square inch. The higher the DPI, the
sharper is image.
Type of printer: Each type of printer has its own capabilities of printing.
Some types of printers produce high quality print while other produce low
quality print.
Print Mode: The printing mode may also affect the quality. For example the
draft mode increases the print rate but quality is reduced.
Toner: The quality and amount of toner also affects print quality.

“Impact Printer”
These printers have a mechanism that touches the paper to create an image.
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.
These printers create an image on the print medium without the use of force.
They don’t touch the paper while creating an image. Non-impact printers
are much quieter than impact printers as they don’t strike the paper.Non-
Impact Printersâ

“Non-Impact Printers”
These printers create an image on the print medium without the use of
force. They don’t touch the paper while creating an image. Non-impact
printers are much quieter than impact printers as they don’t strike the paper.

Dot Matrix Printer

• The term dot matrix refers to the process of placing dots to form an image.
• Its speed is usually 30 to 550 characters per second (cps).
• This is the cheapest and the most noisy printer and has a low print quality.
Dot Matrix were 1st introduced by Centronics in 1970.

How Dot-Matrix works?

• The dot matrix forms images one character at a time as the print head
moves across the paper.
• Uses tiny pins to hit an ink ribbon and the paper much as a typewriter
does.
• This printer arranges dots to form characters and all kinds of images.
• 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. These printers can produce carbon copies along
with the originals.

Advantages/Dis-advatages of Dot-Matrix
Advantagess Dis-advantages:
(1) Inexpensive. (1) Noisy
(2) Low per page cost. (2) Low resolution
(3) Energy efficient. (3) Limited fonts flexibility
(4) Poor quality graphics output.
Ink-Jet Printer
It is a non-impact printer producing a high quality print. A standard Inkjet
printer has a resolution of 300dpi. Newer models have further improved dpi.
Inkjet printers were introduced in the later half of 1980s and are very popular
owing to their extra-ordinary performance.
How Inkjet Printer works?

How Inkjet Printer works?

• Print head having four ink cartridges moves.
• Software instructs where to apply dots of ink, which color and what
quantity to use.
• Electrical pulses are sent to the resistors behind each nozzle.
• Vapor bubbles of ink are formed by resistors and the ink is forced to
the paper through nozzles.
• 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/ Dis-advantages
Advantages: Disadvantages:
High resolution output. Expensive.
Energy efficient. Special paper required for higher resolution
Many options to select. output.
Time consuming in case of graphics printing

Laser Printers
• The primary principle at work in a laser printer is static electricity.
• Static electricity is simply an electrical charge built up on an insulated
object.
• Since oppositely charged atoms are attracted to each other, objects with
opposite static electricity fields cling together.
• The core component of this system is the photoreceptor, typically a
revolving drum or cylinder. This drum assembly is made out of highly
photoconductive material that is discharged by light photons.

• Initially, the drum is given a total positive charge by the charge corona wire,
a wire with an electrical current running through it.
• As the drum revolves, the printer shines a tiny laser beam across the surface
to discharge certain points.
• In this way, the laser "draws" the letters and images to be printed as a pattern
of electrical charges -- an electrostatic image.
• After the pattern is set, the printer coats the drum with positively charged
toner -- a fine, black powder.
– Since it has a positive charge, the toner clings to the negative discharged
areas of the drum, but not to the positively charged "background."

With the powder pattern affixed, the drum rolls over a sheet of paper, which
is moving along a belt below. Before the paper rolls under the drum, it is
given a negative charge by the transfer corona wire (charged roller). This
charge is stronger than the negative charge of the electrostatic image, so the
paper can pull the toner powder away. Since it is moving at the same speed
as the drum, the paper picks up the image pattern exactly.
 To keep the paper from clinging to the drum, it is discharged by the detac
corona wire immediately after picking up the toner.

• Finally, the printer passes the paper through the fuser, a pair of heated
rollers.
• As the paper passes through these rollers, the loose toner powder melts,
fusing with the fibers in the paper.
• The fuser rolls the paper to the output tray, and you have your finished page.
• The fuser also heats up the paper itself, of course, which is why pages are
always hot when they come out of a laser printer.

After depositing toner on the paper,

the drum surface passes the discharge lamp. This bright light exposes the
entire photoreceptor surface, erasing the electrical image. The drum surface
then passes the charge corona wire, which reapplies the positive charge.

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