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CHAPTER 4
INPUT AND OUTPUT
DEVICES
G-S CHEME
BY MR. ARVIND S. SARDAR
LECTURER
MIT POLYTECHNIC ROTEGAON
1
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CONTENTS
KEYBOARD MOUSE
SCANNER
MODEM
PRINTER
LECTURES REQUIRED 06
MARKS 12
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KEYBOARD
TYPES OF KEYBOARD SWETCHES MEMBRANE
MECHNICAL
RUBBER DOME
CAPACITIVE
OPTOELECTRONIC
INTERFACING
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INTRODUCTION
A keyboard is a series of switches connectedto a microprocessor that monitors the state of
each switch and initiates a specific response
to a change in that state.
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INTRODUCTION
Standard Keyboard Layout A standard computer keyboard has about
101 keys.
Most keyboards use the QWERTY layout,
named for the first six keys in the top row ofletters.
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INTRODUCTION
Standard Keyboard Layout Most keyboards have keys arranged in five groups
1. Alphanumeric keys (Typing area)
2. Numeric keypad
3. Function keys
4. Modifier keys
5. Cursor-movement keys (Screen control)
6.Modifier key (windows key)
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INTRODUCTION
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HOW A KEYBOARD W ORKS
A keyboard is a lot like a miniature computer.
It has its own processor and circuitry that carriesinformation to and from that processor.
A large part of this circuitry makes up the key
matrix.
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HOW A KEYBOARD W ORKS
When you press a key:
The keyboard controller detects the keystroke.
The controller places a scan code in the keyboard
buffer, indicating which key was pressed.
The keyboard sends the computer an interruptrequest, telling the CPU to accept the keystroke.
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HOW THE COMPUTER ACCEPTS INPUT FROM THE
KEYBOARD
Keyboard controller Keyboard buffer
Scan code
Interrupt request
Repeat rate
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FROM THE K EYBOARD TO THE COMPUTER
The processor in the keyboard is analyzing the keymatrix and determining what characters to send to
the computer. It maintains these characters in a
buffer of memory that is usually about 16 bytes
large. It then sends the data in a stream to thecomputer via some type of connection.
A PS/2 type keyboard connector.
A USB type of keyboard connector.
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HOW THE COMPUTER ACCEPTS INPUT FROM THE
KEYBOARD
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KEY MATRIX
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PARTS OF KEYBOARD CIRCUITRY
Keyboard controller Keyboard buffer
Scan code
Interrupt request
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TYPES OF KEYBOARD SWETCHES
Capacitive Switch
Two plates of capacitor are brought closerwhen the key Is pressed.
As the two plates move closer together, the
amount of current flowing through the matrix
changes.
The processor detects the change and interprets
it as a key press for that location.
Capacitive switch keyboards are expensive, but
they have a longer life than any other keyboard.
Also, they do not have problems with bouncesince the two surfaces never come into actual
contact.
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TYPES OF KEYBOARD SWETCHES
Membrane Switch
Flat-panel membrane keyboards are most often found on
appliances like microwave ovens or photocopiers.
A common design consists of three layers.
The top layer (and the one the user touches) has the labels printed
on its front and conductive stripes printed on the back. Under this it has a spacer layer, which holds the front and back
layer apart so that they do not normally make electrical contact.
The back layer has conductive stripes printed perpendicularly to
those of the front layer.
When placed together, the stripes form a grid.
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TYPES OF KEYBOARD SWETCHES
Membrane Switch
When the user pushes down at a particular position, their fingerpushes the front layer down through the spacer layer to close a circuitat one of the intersections of the grid.
Typical applications include;
Industrial controls Access control systems
Medical equipment Telecommunications
Telephone systems Household appliances
Security systems
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TYPES OF KEYBOARD SWETCHES
Mechanical Switch
Two metal contacts are kept in open position and
moved into close position when the switch is
depressed.
Very Durable
Mechanical keyboards have proven popular amongstthe PC gaming community.
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TYPES OF KEYBOARD SWETCHES
Rubber Dome Switch
Dome-switch keyboards are a hybrid of flat-panelmembrane and mechanical keyboards.
They use small, flexible rubber domes, each with a hardcarbon center.
When you press a key, a plunger on the bottom of the
key pushes down against the dome, and the carboncenter presses against a hard, flat surface beneath thekey matrix.
As long as the key is held, the carbon center completesthe circuit.
When the key is released, the rubber dome springs backto its original shape, forcing the key back up to its at-rest position.
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TYPES OF KEYBOARD SWETCHES
Rubber Dome Switch
Rubber dome switch keyboards are inexpensive, have pretty good tactile response and are fairly resistant to
spills and corrosion because of the rubber layer
covering the key matrix.
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TYPES OF KEYBOARD SWETCHES
Opto-Electronics Switch
Flat-panel membrane keyboards are mostoften found on appliances like microwave
ovens or photocopiers.
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TYPES OF KEYBOARD SWETCHES
Opto-Electronics Switch Have LED which generates light when proper electric
power is supplied.
Opposite to the LED, A Phoito-transitor is used.
The property of Phoito-transitor is the it allow the current
flow in the circuit , as long as light is applied to it, when
light falling to Phoito-transitor is removed, it will no
longer allow the current to pass through it.
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INTERFACING
A keypad consists of a number of key switches arranged in a
matrix of rows and columns.
In small matrices, rows and columns are connected directly
to the microprocessor I/O lines. In large matrices, decoders
are used to save the number of I/O lines used.
For a 4 4 Hex keypad, there are four rows and four columns.
The rows are high since they are connected to +5V. To
identify a pressed key, the technique is to send a logic 0 on
each column, one at a time, then find out which row as a low
logic. The combination of having logic 0 for both column and
row will identify which key is pressed.
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INTERFACING
A logic 0 is sent down on column 0 first.
If a logic 0 is detected at row 0, it means that key-0 has been
pressed. If a logic 0 is detected at row 1, it means that key-4has been pressed. The process is repeated for all 4 rows.
Then a logic 0 is sent down on column 1 and try to find out
which row received this signal and thus which key has been
pressed. The same is repeated for column 2 and 3.
Note: The pull-up resistors are not built-in inside the
keypad, they are all external components.
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S WITCH BOUNCE
Mechanical switches tend to bounce. When the switch makes
or breaks, it makes a number of very rapid make and break
actions before the contacts become stable. This bouncing tells the microprocessor that the switch has
been pressed a few times instead of once which means that
false information has been sent to the MCU and misled it.
To debounce a switch, a software time delay is used that
provides a time delay (20~30 ms) longer than the duration ofthe switch bouncing action.
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KEYBOARD CONNECTOR
The keyboard connector is the device at the end of the cable
that is used to attach the keyboard to the system.
There are Three standard types of connectors.
The 5-pin DIN
The 6-pin / "mini-DIN“ / PS/2
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KEYBOARD CONNECTOR
Pin # 5-pin DIN Connector 6-pin "mini-DIN" Connector
1 Keyboard Clock Keyboard Data
2 Keyboard Data (not connected)
3 (not connected) Ground
4 Ground Power (+5V)
5 Power (+5V) Keyboard Clock
6 -- (not connected)
C
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KEYBOARD CONNECTOR
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COMPARISON OF KEY SWITCH TECHNOLOGIES
Type Technology TravelTactile
Feedback
Audible
Feedback"Feel" Durability Cost Commo
Contact
Mechanical High High High Hard, solid High High Lo
Foam and
Foil
Moderate
to HighLow Low Soft, quiet
Low to
ModerateLow
Low
Mode
Rubber
Dome
Moderate
To HighModerate
Low to
Moderate
Moderate,
springyModerate
Low to
ModerateHig
Membrane LowLow to
Moderate
Low to
Moderate
Hard,
springy
Moderate to
HighLow
Low (f
Keybo
Capacitive Capacitive High High High Hard, solid Very High Very High Lo
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MOUSE
Opto-mechanical
Optical ( New design)
WHAT IS A MOUSE?
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WHAT IS A MOUSE?
The mouse is a pointing device. You use it to move a
graphical pointer on the screen.
The mouse can be used to issue commands, draw, and
perform other types of input tasks.
M T
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MOUSE TECHNIQUES
Using the mouse involves five techniques: 1. Pointing: Move the mouse to move the on-screen pointer.
2. Clicking: Press and release the left mouse button once.
3. Double-clicking: Press and release the left mouse button twice.
4. Dragging: Hold down the left mouse button as you move the
pointer.
5.Right-clicking: Press and release the right mouse button.
TYPES OF MOUSE
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T YPES OF MOUSE
Types of mouse
Based on technology
Mechanical
Opto -
Mechnical
Optical
Based on buttons
Singel
Double
Three
Scroll
Based on Interface
Serial
Bus
Mouse port
Wireless
USB
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OPTO- MECHNICAL MOUSE
An Optomechanical or optical-mechanical mouse is same as
the mechanical mouse except that the sensors used in it areoptical and not mechanical. The device is a combination of
optical and mechanical technologies, wherein, the ball is
present but the mouse movement is detected optically
leading to more accuracy.
OPTO MECHNICAL MOUSE
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OPTO- MECHNICAL MOUSE
1. moving the mouse turns the
ball.2. X and Y rollers grip the ball
and transfer movement
3. Optical encoding disks
include light holes.4. Infrared LEDs shine
through the disks.
5. Sensors gather light pulses
to convert to X and Yvectors.
OPTO MECHNICAL MOUSE
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OPTO- MECHNICAL MOUSE
OPTICAL MOUSE
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OPTICAL MOUSE An optical computer mouse uses a
light-emitting diode and photodiodesto detect movement relative to a
surface, unlike a mechanical mousewhich has a ball which rotatesorthogonal shafts which drive chopperwheels for distance measurement.
The main components of the optical
mouse are:
Inbuilt optical sensor
High speed camera which can take1000 pictures at a time
LED
OPTICAL MOUSE WORKING
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OPTICAL MOUSE - WORKING
These optical mouse do have an inbulit optical sensor.
The optical sensor reads the movements of the optical mouse
(moved by the user) with the help of the light rays whichcomes out from the bottom.
When the user moves the optical mouse, the LED (LightEmitting Diode) present inside the mouse emits the lightaccording 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 everypictures and compared to one another with the digitaltechnology.
With the comparison, the speed of the mouse and the directionof the movement of the mouse are rapidly calculated.
According to the calculation, the pointer moves on the screen.
OPTICAL MOUSE
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OPTICAL MOUSE
BLOCK DIAGRAM OF AN OPTICAL MOUSE
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BLOCK DIAGRAM OF AN OPTICAL MOUSE
COMPARISON BETWEEN A
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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 theordinary mouse.
Since the mouse works with the sensor recognition, themovements are clearly captured and so the moves gives out asame function in all moves.
Since the ball is absent in the optical mouse, the weight of theoptical mouse is less than that of the ball mouse.
The dust clustering problem is abolished in the optical mouse asits 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 glassmaterials.
SCANNER
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SCANNER
Flat Bed
Sheet-fed Handheld
Block diagram of flat Bed and specifications
OCR
TWAIN
Resolution
Interpolation.
SCANNER
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SCANNER
Scanner is a special input device to convert both picture and text into
stream of data.
A scanner, simply put, is a device used to analyze an image
and process it.
Bring existing image into the computer.
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SHEET-FED SCANNER
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SHEET FED SCANNER
More portable than a flatbed
scanner
Used to scan paper documents and
photos
The paper moves through thescanner
Usually smaller than a flat-bed and
portable
HANDHELD SCANNER
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H ANDHELD SCANNER
Smaller than the previous two
scanners
The user must move the scanner
across the document
Image quality is usually lower
DRUM SCANNER
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DRUM SCANNER
Used by the publishing industry
Document is placed on a glass
cylinder
Generates very high-quality scans
USING Y OUR SCANNER
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Most flatbed scanners are connected to the computer via
the Universal Serial Bus (USB).
A software program called a TWAIN driver is used by the
computer to communicate with the scanner.
An image editing program can then be used to manipulatethe scanned image.
Most modern scanners connect to the computer through the
USB.
P ARTS OF SCANNER
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Charge-coupled device (CCD) array
Mirrors
Scan head Glass plate
Lamp
Lens
Cover
Filters Stepper motor
Stabilizer bar
Belt
Power supply
Interface ports) Control circuitry
WORKING OF SCANNER
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BLOCK DIAGRAM OF FLAT BED SCANNER
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BLOCK DIAGRAM OF FLAT BED SCANNER
BLOCK DIAGRAM OF FLAT BED SCANNER
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BLOCK DIAGRAM OF FLAT BED SCANNER
Paper
Motor
and motor
control
A/D
Converter
Latch
Interface
And
control
Light Source
Reflector
Light sensitive
Diode
C
a
r
r
ia
g
e
T
C
SCANNING FORMATS
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Depending on your scanning software, you may
have different options of file formats in which tosave your scanned image or document.
Images may be saved as
jpg, bmp, tif, or png.
Documents may be saved as
pdf or any of the image formats
OCR
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OCR Optical character Recognition is a process of scanning printed
pages as image on scanner and then using OCR software to recognize
the letter as ASCII text.
Converting images with printed text to text format
Making printed text accessible for text utils
Sources: scans, screenshots, photos?, pdf's, edocs
Destination: ASCII/UTFtext, HTML/XML, TeX
OCR
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OCR systems consist of four major stages :
Pre-processing
Segmentation
Feature Extraction
Classification
Post-processing
TWAIN
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The TWAIN is a standard of communication between the
computer and scanner that allow images to be directly
scanned from an image editing program. All scanner
manufacturers agree to use this standard.
The TWAIN driver controls the scanner and serves as the
interface between the scanner and your graphics program.
TWAIN is not an acronym for anything.
Twain is an old form of the word“two
”.
The TWAIN software refers to the computer and scanner and
the difficulty in connecting the two.
TWAIN
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Multiple platform support
Support for multiple devices
Wade sprade acceptance Extensibility and revisions
Easy implementation
Longevity
Multi data capacity
INTERPOLATION
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Is a process to increase the perceived resolution of an image.
This occur by creating extra pixeles in betwwen the ones actually
scanned by the CCD array.
Resolution : Image resolution is the detail an image holds.
MODEM
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Internal
External Block diagram and specifications
MODEM
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Modem Short for modulator-demodulator. A modem is a
device or program that enables a computer to transmit data
over, for example, telephone or cable lines. Computer
information is stored digitally, whereas information
transmitted over telephone lines is transmitted in the form of
analog waves. A modem converts between these two forms.
MODEM CONNECTION
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DTE DTEDCE DCE
110011 110011modem
PC
modem
PC
MODEM
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An input/output device that converts digital data from acomputer to analog data for transmission over the telephonelines by modulating it into waves; at the other end, the modemconverts the analog data back to digital form so that it can beread by the computer. Modems are made for differentfrequencies from 28.8k bps to 56k bps (bps – Bit Per Second)
There is one standard interface for connecting external modemsto computers called RS-232.
Types of modem
There are two types of modem
Internal modem
External Modem
MODEM
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1. Internal Modem:
Internal modems are built into the motherboard or a circuit board that plugs into
an expansion slot inside a computer. Internal modems are also known as analogor dial-up modems. Modern analog modems transfer information at about 56kilobits per second (56K) over a telephone line.
Analog dial-up modems are susceptible to phone-line noise or interference fromelectrical devices and slower internet connection speeds. However, 56K dial-upmodems can be used anywhere a phone line is available.
2. External Modem: The modem which is placed outside the computer is called External Modem.
External modems are portable devices that you can attach to a serial or USB(Universal Serial Bus) port on your computer.
External modems can be disconnected from your computer and used with othercomputers.
MODEM CONNECTION
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BLOCK DIAGRAM INTERNAL MODEM
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BLOCK DIAGRAM – INTERNAL MODEM
B U
S
UART
ADDRESS
DECODER
Modulator
Demodelator
Telephone
interface
controllerNVRAM
RJ 11
Telephone l
connector
BLOCK DIAGRAM EXTERNAL
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BLOCK DIAGRAM EXTERNAL
controllerNVRAM
Modulator
Demodulator
Telephone
Interface
RJ 11
Telephone
connector
TECHNICAL SPECIFICATIONS
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Data rate: 14400, 12000, 9600, 7200, 4800, 2400, 1200, and 0-300BPS
Fax rate: 14400, 12000, 9600, 7200, 4800, and 2400 BPS
Data compression: MNP-5 and V.42bis
Error correction: MNP2-4 and V.42
Data operation: Full and half duplex
Dialing mode: Rotary and touch-tone
Data compatibility: CCITT V.32bis, V.32, V.22bis, V.22, V.21, V.23and Bell 103 and 212A
Fax compatibility: ITU-T V.17, V.33, V.29, V.27ter, and V.21(Channel 2)
Data commands: "AT" compatible command set
Fax commands: Class 2 fax command interface
Phone connectors: RJ-11C
Internal bus interface: ISA
DIFFERENCE BETWEEN INTERNAL AND
EXTERNAL MODEM
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EXTERNAL MODEM
Item Description
ExternalModem
This particular modem uses a serial interface (connection):
(compare the pros and cons)
+ Easy to install with serial cable
+ Does not occupy internal slot
+ Does not draw from computer’s power supply
+ Has LED indicator light, which make it easier to diagnose problem
+ Can be turned off without turn off the computer
•Uses a serial port for connectivity
•Slightly higher because of case, power supply, and cable.
Internal Modem This particular modem goes inside your PC in an ISA or PCI
expansion slot. (compare the Pro and Cons)
+ Usually supply it own port
+ Provides own high-speed UART
+ Slightly Less Expensive
•Occupy an internal expansion slot
•Some Models offers a windows display of progression for connectivity.•In some situation, lockup of modems can only be cured by resetting
entire computer.
PRINTER
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Printer Characteristics
Dot matrix
Inkjet
Laser :Block diagram and specifications.
PRINTER
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A printer produces a paper copy of information
generated by a computer.
Printers fall into two categories: Impact printers use a device to strike an
inked ribbon, pressing ink from the
ribbon onto the paper.
Non-impact printers use different
methods to place ink (or anothersubstance) on the page.
T YPES OF PRINTERS
D t M t i P i t
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Dot Matrix Printers
Ink Jet Printers
Laser Printers Snapshot Printers
Other High-Quality Printers
TYPES OF PRINTERS CONT.
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T YPES OF PRINTERS CONT.
Dot matrix printer – Dot-matrix printers were
once very popular, but have been replaced inpopularity by ink-jet p5rinters. Dot-matrixprinters typically use continuous form multipapaper and are commonly used for documents
such as sales invoices and purchase orders.
Inside a dot-matrix printer a print headcontaining small blunt pins strikes an inkedribbon to stamp images on a page.
TYPES OF PRINTERS CONT.
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T YPES OF PRINTERS CONT.
•
Dot Matrix: Been around since the first PCs. Use mechanical means to press ink from ribbon onto page.
9 or 24 pin print head 9pins == low quality and 24 pin has smaller pins close to each
other giving better quality print (Near Letter Quality (NQL). Various size and shape ribbon cartridges
Multipart forms: Carbonless paper forms keep these printersaround.
Tractor feed and friction feed Uses a sprocket to mesh with holes in the side of continuous
form paper. Typewriters use friction feed.
T YPES OF PRINTERS CONT.
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75Peter Norton’s Introduction to Computers 4th Edition
T YPES OF PRINTERS CONT. Dot-matrix printers are two important characteristics :
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Speed : Given in characters per second (cps), the speed can vary from about 50 to over 500 cps. Most dot-matrix printers offer differen speeds depending on the quality of print desired.
Print Quality : Determined by the number of pins (the mechanisms that print the dots), it can vary from9 to 24. The best dot-matrix printers (24 pins) can produce near letter-quality type, although you can stillsee a difference if you look closely.
Advantages :
can print on multi-part stationery or make carbon copies.
Impact printers have one of the lowest printing costs per page.
They are able to use continuous paper rather than requiring individual sheets.
The ink ribbon also does not easily dry out.
Disadvantages :
Impact printers are usually noisy.
They can only print low resolution graphics, with limited colour performance, limited quality andcomparatively low speed.
They are prone to bent pins (and therefore a destroyed printhead) caused by printing a character half-onand half-off the label.
T YPES OF PRINTERS CONT.
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Ink-jet Printer – An ink-jet printer produces
high-quality documents at a relatively low pric
You can use the documents produced by an ink
jet printer in most circumstances, except when
only the highest quality is acceptable, such as
important business correspondence.
An ink-jet printer sprays ink through small
nozzles onto a page to produce images.
T YPES OF PRINTERS CONT.
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78
Peter Norton’s Introduction t
Computers 4th Edition
T YPES OF PRINTERS CONT.
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Laser Printer – A laser printer is a high-speed printhat is ideal for business documents and graphics. La
printers produce the highest quality images, but arerelatively expensive.
A laser printer works like a photocopier to produceimages on a page. A laser beam draws images on a
light-sensitive drum. The drum picks up a finepowdered ink called toner, and then transfers the tonto the paper to create the images.
Laser printers produce higher-quality print than inkprinters, but are more expensive.
T YPES OF PRINTERS CONT.
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80
Peter Norton’s Introdu
to Computers 4th Edi
T YPES OF PRINTERS CONT.
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81
Peter Norton’s Introduction to Computers 4th Edition
CHOOSING A PRINTER
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Before choosing a printer, the following
features should be researched:
Print Quality – The type of printer you should
choose depends on the quality of the printed
pages you require.
Speed –
Printer speed indicates how quickly aprinter can produce printed pages.
CHOOSING A PRINTER
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Resolution – Printer resolution determines the
quality of the images the printer can produce.
Software – Most printers intended for home sue
include software you can use to create special
documents, such as greeting cards.
CHOOSING A PRINTER
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Consumables – All printers require itemsthat have to be replaced on a regular basis,such as ink or toner. Make sure you areaware of how they cost.
Print Media – when choosing a printer, you
should check the size and type of paper theprinter accepts. If you are going to need toprint on envelopes and labels, make surethe printer has that feature.
CHOOSING A PRINTER C l C l i ll
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Color – Color printers usually use cyan,
magenta, yellow and black ink to create color
images on a page. Color ink jet printers are themost popular because they are less expensive.
Warranty – The length of a printer warranty
may range from 90 days to one year. Consider
an extended warranty or service contract foryou printer.
CONNECTION AND SET UP B f ti i t t ff th
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1. Before connecting a printer, turn off thecomputer.
2. If necessary, remove any spacers or tape usedto secure the printer's internal componentsduring shipping. Then assemble the printeraccording to the instructions in the printer’sdocumentation.
3. Connect the printer cable to the port on theprinter.
CONNECTION AND SET UP
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4. Connect the printer cable to a parallel po
the back of the computer. Some printersconnect to a USB port.
5. Connect the power cable to the powerconnector on the printer.
6. Plug the power cable into an electrical ou7. All printers require a driver to operate. A
driver is the software that allows thecomputer’s operating system to communwith and control the printer.
NETWORK PRINTERS
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• Connect straight through cable from NIC onprinter to a live network feed ethernet port
• Assign a static IP address to the printer
• Configure any network computers with corr
printer software drivers
• Verify connection with the “ping” CLI comm
CONNECTION AND SET UP B f ti i t t ff th
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1. Before connecting a printer, turn off the
computer.
2. If necessary, remove any spacers or tape used
to secure the printer's internal components
during shipping. Then assemble the printer
according to the instructions in the printer’s
documentation.3. Connect the printer cable to the port on the
printer.
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