Display

Display
A single bit is needed for each pixel (2
brightness level)
Termed bit mapped
For gray scale or color image require
more pixels
Very good gray scales with 8 bits/pixel
(256 shades)
for photographic quality require 24 bits



CRT display
Flat panel display (LCD




Use rater-scan technology
Beam of electron is sent to the screen
Causes the phosper coated screen to
emit light forming an image
Resolution is measured by the no of
vertical and horizontal pixels

Flat Panel Display


Thinner and lighter
Most common is the LCD
Thin Film Transistor (TFT) are
becoming more popular

Data Capture Devices

Special p[purpose devices intended for us
in particular applications
Direct Data Input Devices
Sensing devices
Detect and pass the data directly to the
computer
i.e.
Production line
Supermarket checkout
In chemical works, Food factory or brewery
Bar Codes

In many libraries, every book has a bar-code
inside the front cover. This contains a number
which uniquely identifies the book. Each user
of the library is issued with a card which also
has a bar code printed on it. The coded
number uniquely identifies the user.
The library counter has on it a number of
terminals. These are connected directly to the
county library’s central computer. Each
terminal has a bar code reader in the form of
a hand-held ‘wand’.
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When a book is taken out, the librarian uses
the wand to read the bar code on the book
and then the bar code on the borrower’s card.
The central computer receives these
numbers and records the book loan in a
loans file.
When the book is returned, the librarian uses
the wand to read the bar code in the book.
This is automatically transmitted to the main
computer which deletes the loan from the
loans file.
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Magnetic Strip Cards




Advantages :
Easy and cheap to produce.
Not easily damaged.
Each stores a fairly large number of
characters (about 72)


Cuts down the amount of writing involved in a
transaction.
Disadvantages.
The data can be changed or erased by
magnetic fields.
The stripe can be damaged by scratching.
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Smart Cards
These have very thin memory chips
sealed into them. Some of the data in
them can be changed. One card can store
about 8000 characters.

Scanners

Parts of a Scanner
Charge-coupled device (CCD) array
Mirrors
Scan head
Glass plate
Lamp
Lens
Cover
Filters
Stepper motor
Stabilizer bar
Belt
Control circuitry




Charge Coupled device (CCD)
One of the two main types of image sensors
used in digital cameras.
When a picture is taken, the CCD is struck by
light coming through the camera’s lens.
Each of the thousands or millions of tiny
pixels that make up the CCD convert this light
into electrons.
The number of electrons, is then converted to
a digital value.




Document Reader
Data is read directly from the source
documents.
Mark reader
Character Reader

Mark Reader
Sends a thin beam of light on to the paper
Detects the reflected light
Dark pencil mark absorbs the beam
i.e. Multiple choice examination

Optical Character Reader
Alphabets and numbers can be read by
special machines
Can also be read by human
Uses a light source to read characters
Converts them into electrical signals
Sends to the computer for processing

OCR
Application
One useful application of OCR is in the
processing of turnaround documents. A
turnaround document is a document printed by a
computer. Later, when extra data has been
added, the document is read by an OCR reader
and the data is input to the computer for
processing.
For example, turnaround documents may be
used by gas or electricity boards to collect meter
readings from all their customers. The stages in
the data processing are....
The computer prints out a meter reading sheet
for each customer in an OCR font showing their
name, address, meter number and other details
The meter readers read the meters and add the
readings to each sheet. They may use careful
hand-written figures to record the readings.
The completed meter reading sheets are input
using an OCR reader, and the computer
produces the bills.
OCR reader speeds of up to 1500 sheets per
minute may be expected.

Mouse

Pointing Devices

Pointing Devices
• Mouse
Most commonly used with an on screen cursor
Main input device for a GUI
• Trackball
A stationary mouse upside down
• Joystick
Operates like an aircraft joystick
Returns to central position when released

Keyboard

 Most widely used input device
 Style adapted form the typewriter
 Differs due to the inclusion of the CTRL key
 Extra sections in the keyboard
I. Function keys
II. Cursor / screen positional keys
III. Numeric keypad
IV. Indicator lights

Input and Output Devices

�� Input Devices
Keyboard Entry
Pointing Devices
Scanners
Document Readers
OMR, OCR, MICR
Bar Codes
Magnetic Strip Cards
�� Output Devices
CRT Screens
Flat Panel Screens
Printers



Overview