Polytechnic Input output devices

8/13/2019 Polytechnic Input output devices

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CHAPTER 4

INPUT AND OUTPUT

DEVICES

G-S CHEME

BY MR. ARVIND S. SARDAR

LECTURER

MIT POLYTECHNIC ROTEGAON

CONTENTS

KEYBOARD MOUSE

SCANNER

PRINTER

LECTURES REQUIRED 06

MARKS 12

KEYBOARD

TYPES OF KEYBOARD SWETCHES MEMBRANE

MECHNICAL

RUBBER DOME

CAPACITIVE

OPTOELECTRONIC

INTERFACING

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.

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.

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)

INTRODUCTION

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.

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.

HOW THE COMPUTER ACCEPTS INPUT FROM THE

KEYBOARD

Keyboard controller Keyboard buffer

Scan code

Interrupt request

Repeat rate

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.

HOW THE COMPUTER ACCEPTS INPUT FROM THE

KEYBOARD

KEY MATRIX

PARTS OF KEYBOARD CIRCUITRY

Keyboard controller Keyboard buffer

Scan code

Interrupt request

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.

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.

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

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.

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.

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.

Opto-Electronics Switch

Flat-panel membrane keyboards are mostoften found on appliances like microwave

ovens or photocopiers.

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.

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.

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.

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.

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

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)

KEYBOARD CONNECTOR

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

Moderate

to HighLow Low Soft, quiet

Low to

ModerateLow

Rubber

Moderate

To HighModerate

Low to

Moderate

Moderate,

springyModerate

Low to

ModerateHig

Membrane LowLow to

Moderate

Low to

Moderate

springy

Moderate to

HighLow

Low (f

Capacitive Capacitive High High High Hard, solid Very High Very High Lo

Opto-mechanical

Optical ( New design)

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.

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

T YPES OF MOUSE

Types of mouse

Based on technology

Mechanical

Opto -

Mechnical

Optical

Based on buttons

Singel

Double

Scroll

Based on Interface

Serial

Mouse port

Wireless

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

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

OPTICAL MOUSE

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

OPTICAL MOUSE WORKING

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

BLOCK DIAGRAM OF AN OPTICAL MOUSE

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 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

Flat Bed

Sheet-fed Handheld

Block diagram of flat Bed and specifications

Resolution

Interpolation.

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.

SHEET-FED SCANNER

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

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

Used by the publishing industry

Document is placed on a glass

cylinder

Generates very high-quality scans

USING Y OUR SCANNER

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

P ARTS OF SCANNER

Charge-coupled device (CCD) array

Mirrors

Scan head Glass plate

Filters Stepper motor

Stabilizer bar

Power supply

Interface ports) Control circuitry

WORKING OF SCANNER

BLOCK DIAGRAM OF FLAT BED SCANNER

and motor

control

Converter

Interface

control

Light Source

Reflector

Light sensitive

SCANNING FORMATS

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 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 systems consist of four major stages :

Pre-processing

Segmentation

Feature Extraction

Classification

Post-processing

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.

Multiple platform support

Support for multiple devices

Wade sprade acceptance Extensibility and revisions

Easy implementation

Longevity

Multi data capacity

INTERPOLATION

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.

Internal

External Block diagram and specifications

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

DTE DTEDCE DCE

110011 110011modem

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

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

BLOCK DIAGRAM INTERNAL MODEM

BLOCK DIAGRAM – INTERNAL MODEM

ADDRESS

DECODER

Modulator

Demodelator

Telephone

interface

controllerNVRAM

Telephone l

connector

BLOCK DIAGRAM EXTERNAL

controllerNVRAM

Modulator

Demodulator

Telephone

Interface

Telephone

connector

TECHNICAL SPECIFICATIONS

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

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

Printer Characteristics

Dot matrix

Inkjet

Laser :Block diagram and specifications.

PRINTER

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

Dot Matrix Printers

Ink Jet Printers

Laser Printers Snapshot Printers

Other High-Quality Printers

TYPES OF PRINTERS CONT.

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.

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.

75Peter Norton’s Introduction to Computers 4th Edition

T YPES OF PRINTERS CONT. Dot-matrix printers are two important characteristics :

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.

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.

Peter Norton’s Introduction t

Computers 4th Edition

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.

Peter Norton’s Introdu

to Computers 4th Edi

Peter Norton’s Introduction to Computers 4th Edition

CHOOSING A PRINTER

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

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

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

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

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

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

• 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

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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