Input and Output Devices

Question 1

2-D Scanner (Working)

Answer 1

Generally Used for converting a HARD COP to into electronic form

The cover is raised and the document is placed facing downward on the glass and the lid is closed.
A bright light illuminates the document while a SCAN HEAD moves across the document. With
the help of mirrors the image produced is sent to a LENS focused on the document.
The Scanned image falls on a CHARGED COUPLE DEVICE (CCD) which is made up thousands of pixels that create an electrical charge when light falls on them .
Which results in the production of an DIGITAL IMAGE from the electronic form.

Question 2

2-D Scanner Application

Answer 2

Computers that come equipped with OCR (Optical Character Recognition) can allow the scanned text to be converted into
TEXT FILE where it can be edited using a WORD PROCESSOR.

Question 3

3-D Scanner Working

Answer 3

Scans SOLID OBJECTS to create 3D image (x,y,z coordinates) to be later used in Computer Aided Software (CAD) or even
printed (3D printer). Methods include laser, resonance, white light and so on.

Computed Tomographic (CT) Scanners rely on a TOMOGRAPHY method in which a 3D Image is ‘built up’ using very thin
2D ‘slices’. Each Slice is essentially built up using X-Rays, radio frequencies or gamma imaging. These slices are then stored as
a ‘digital’ image. A Tomographic Scanner can make use of the following techniques:-
• X-Rays (CT Scanners)
• Radio Frequencies (MRI) a.k.a Magnetic Resonance Imaging.
• Gamma Rays a.k.a single photon emission computed tomography (SPECT).

Question 4

3-D Scanner Application

Answer 4

• CAD

* 3D Printing

Question 5

Bar Code Scanner Working

Answer 5

A BARCODE is a series of dark and light lines of varying thickness. Standards such as UPC use these lines to represent the
numbers 0to 9. Each digit is represented by bars that 1 to 4 blocks thick. The barcode is separated into a LEFT HAND SIDE
and RIGHT HAND SIDE.

• Each digit is represented by TWO DARK LINES and TWO LIGHT LINES. Each digit is represented using the
SAME WIDTH.
• The numbers on the LEFT have ODD NUMBER OF DARK ELEMENTS and always start WITH WHITE BAR.
The numbers of the RIGHT HAVE EVEN NUMBER of dark elements and always start WITH A DARK BAR. Due
to which the barcode can be scanned in either direction.
• When a barcode is canned using LED (or RED LASER) little or no light is reflected from the DARK LINES.
• These Reflections are detected by sensors which allows for a pattern to be generated so that the barcode can be
understood. For example a left 3 will look like LDDDDLD (L=Light/0 and D = Dark/1) or 0111101

Question 6

Car Code Scanner Application

Answer 6

• When a barcode is read it represents a KEY FIELD in the items’ database. The key field is used to retrieve details
regarding the item (usually presented on the POS-Point of Sale terminal screen). Once the item is scanned, the
quantity is reduced by one and the changes are sent back to the DB. If the quantity reaches re-order level a request is
sent to suppliers automatically and FLAG is set to represent this (AUTOMATIC STOCK CONTROL).
• Barcodes allow for easier change in prices
• More updated sales information.
• Automatic Stock Control.
• With barcodes buying patterns can also be identified.
• It also allows for faster checkouts and itemised bills.
• Reduction of errors.

Question 7

QR Code(Quick Response Code) Working

Answer 7

It is another type of Barcode that is made up of a matrix of filled-in dark squares on light background.
Normal Barcodes can store UP TO 30 digits only, whereas, QR code can store over7000 digits.

• Using a modern smartphone and the appropriate application the QR code (that can be a website link, phone
number, GPS coordinates) is scanned.
• The phone will then use its Internet Connection to retrieve the information portrayed by the QR code on the screen
without typing anything.

Question 8

QR Code Application

Answer 8

• Is a very effective method for advertising products in public places.
• Can also hold promotional codes etc.

Question 9

Digital Camera Working

Answer 9

digital cameras can be linked to a computer through USB ports/cables or Bluetooth.

• The microprocessor can control features like shutter speed, image focus, flash, aperture size, size of image and
removal of “red eye” effect.
• When Light passes through the lens it lands onto light sensitive cell that is made up many pixels.
• The number of pixels determines the size and quality of image. The quality is also dependent of factors such as light
and types of lens.

Question 10

Digital Camera Application

Answer 10

• Mobile phones have very quickly started to use this technology. However, today’s phones are limited by the quality of
their lens and storage size.

Question 11

Keyboards Working

Answer 11

It is still probably the most common data entry method. It may be slow, prone to errors but it is also the easiest method used.
Tablets and Mobile phones make use of an ONSCREEN keyboard as opposed to physical keyboard.

• Each character on the keyboard represents an ASCII value (Unit 2).
• When a key is pressed it essentially causes a circuit to close resulting in a signal being sent to the processor where it is
interpreted according to the ASCII value.

Question 12

Keyboards Application

Answer 12

• It is the easiest method however, it is also causes REPETETIVE STRAIN INJURY (RSI) due to excessive use.
• RSI can be reduced with Ergonomic Keyboards which has keys arranged in a more comfortable manner.

Question 13

Pointing Devices Working

Answer 13

Selecting items on a screen can be carried out by pointing devices such as Mouse, Tracker Ball, Touch Pad or Touch Screen

• A traditional mouse made use of a mechanical ball arrangement the movement of which (along an X and Y plain) is noted and the represented on computer connected via USB. The more recent technology known as optical mouse makes use of a red LED that can detect movement on a surface(mouse mat or paper). The latter can be seen as a WIRELESS mouse as well connected via Bluetooth.
• Instead of a mouse moving, Tracker Balls make use of a larger ball that is moved for curser movement instead of the mouse itself.
• Both tracker balls and mouse have additional buttons for selection and scrolling.
• Touch pads make use of a tactile sensor which allow the user to move a cursor by simply moving a finger across the surface of the pad. They too have buttons for selection (which can also be replicated by “tapping” the touch pad.

Question 14

Pointing Devices Application

Answer 14

• Mouse are the most common pointing device.
• However, if space is limited or if you want to reduce the chances of RSI Tracker Balls and Touch Pads come in
handy.
• Touchpads are also the standard pointing devices in laptops.

Question 15

Capacitive Touch Screens

Answer 15

made up of many layers of glass that act like a capacitor creating electric fields between the glass plates in layers
when top layer is touched electric current changes and coordinates where the screen was touched is determined by on board micro processor

medium cost, good screen visibility, multi touch compatibility, durable

only bare finger tips can be used as a form of input and in latest models special stylus can also be used

Question 16

Infra-red Screen

Answer 16

Heat Sensitive:
glass is screen material
warm object required to carry out input operation

Optical:
glass is screen material
uses array of sensors in a grid form and point of contact is determined by grid coordinate touched

multi touch capability
optical allow bare fingers gloves or stylus for input
good screen durability

relatively expensive
heat-sensitive only allows bare fingers
fairly good screen visibility in strong sunlight

Question 17

Resistive Screens

Answer 17

Upper layer of polyester and bottom layer of glass
when the top layer is touched it contacts the bottom layer completing the circuit
Signals are sent which are interpreted by the microprocessor that carries out calculations to determine the coordinates of where the screen was touched

relatively inexpensive
bare fingers gloves or stylus can be used

poor screen visibility in strong sunlight
no multi touch capability
screen is vulnerable to scratches and wears out over time

Question 18

Microphones Working

Answer 18

Microphones pick up sound causing diaphragm to vibrate producing an electric signal. This electrical signal goes to a sound card where it is converted to digital values for computer use/storage.

• Voice Recognition systems detect a user’s voice and converts it into digital values. The words spoken produce a wave pattern. If the pattern produced is the same the pattern saved then the person can be correctly identified.

• Speech Recognition on the other hand is more complex as it doesn’t try to recognise the person talking, in fact it tries
to recognise the words spoken so that they can be used for various computer applications. In such systems the sound
card will take convert the sound into digital form where it will be broken into phonemes (the smallest units that
make up any language). These phonemes are then compared to words found in the built in dictionary.

Question 19

Microphone Application

Answer 19

• Both voice recognition and speech recognition can be used together in various applications for example a car can be
designed to take specific voice commands (speech recognition) from the driver only (voice recognition).

Question 20

Sensors

Answer 20

It is a input device that can read or measure physical quantities in ANALOGUE FORM.
Analogue data means that it’s constantly changing and there no discrete values as a result of which readings generated by
sensors can have INFINITE number of values depending on precision which makes them IMPOSSIBLE for computer to
understand. That is why an Analogue to Digital Converter (ADC) is used to convert the data to binary system.

Temperature:-
Humidity:-
Light:-
Infra-Red / Motion:-
Pressure:-
Acoustic/ Sound:-
Gas( O2 or CO2 ):-
pH:-
Magnetic Field:-

Question 21

Ink Jet Printer

Answer 21

• A Print Head that is made up of nozzles that spray droplets of ink to form characters on paper.
• Ink cartridges (colour that are grouped to have Red, Green and Blue Ink as well as a Black Cartridge)
• A stepper motor and belt that moves the cartridges from side to side across the paper while printing.
• Paper tray that automatically feeds paper to the printer while printing.
Ink Droplets can be formed using two different technologies:-
Thermal Bubble make use of tiny resisters that generate high temperatures in a tiny area so that when ink comes in contact a
vapor bubble is created causing the ink to eject form nozzle
The Piezoelectric Technique makes use of a crystal behind each nozzle that essentially vibrates when given a charge causing the ink to be forced out of the nozzle an onto the paper.

Question 22

Ink Jet Printer Working and Application

Answer 22

Working:-
1. Data is sent to the printer driver.
2. The driver makes sure that data is the appropriate format for printing.
3. It also makes sure that the printer is ready and available.
4. The data is sent to the printer buffer where it is stored whilst waiting to be printed.
5. After a sheet is fed to the printer the head starts moving from side to side printing the document.
6. At each complete movement of the head across the sheet of paper the sheet is moved a little so that printing can be done on the next line.
7. When buffer is empty more data is sent for printing with the help of an INTERRUPT until there is no more.
Application:-
INKJET PRINTERS are best for one-off photos or where only a few pages of good quality, color printing are needed; the small ink cartridges or small paper trays would not be an issue with such applications.

Question 23

Laser Jet Printer

Answer 23

print document using powders (toner) instead of liquid ink. With the help of STATIC ELECTRICITY and heating these printers are capable of printing documents at a much faster rate. they are also capable of printing documents in one go.
Working:-
Steps 1 to 4 are the same as Inkjet Printer
5. A drum is given a POSITIVE CHARGE. As the drum rotates a LASER focuses on certain parts of the drum and removes
the charge leaving a NEGATIVELY CHARGE pattern of characters to be printed.
6. The drum is then coated with POSITIVELY CHARGED toner that sticks to the negative charged places.
7. A negatively charged sheet is then rolled over the drum so that the positively charged toner sticks to the paper. The Charge
on the paper is then removed to avoid the paper sticking to the drum.
8. The paper with the powdered ink is then passed through heated rollers which melt the toner onto the paper permanently.
9. A discharge lamp removes all charge from the drum to prepare for printing the next page.
Application:-
LASER PRINTERS produce high quality printouts and are very fast when making multiple copies of a document; any
application that needs high- volume printing (in colour or monochrome) would choose the laser printer (for example, producing
a large number of high quality flyers or posters for advertising) they have two advantages: they have large toner cartridges and
large paper trays (often holding more than a ream of paper)

Question 24

3D Printers

Answer 24

3D Printers are used alongside CAD to create solid objects that actually work using materials like powdered resin, metal, paper
or even ceramic powder.
• 3D printers follow the process of ADDITIVE manufacturing where product is “built-up” layer by layer or
SUBTRACTIVE manufacturing where product is created by “removing” or “carving” unwanted parts from a solid object.
• Direct 3D Printing uses a technology similar to Inkjet Printing however, as opposed to moving only from side to side the
print head can also move up and down to build layers of an object.
• Similarly, Binder 3D Printing involves two passes of forming layers, the first pass sprays dry powder whereas the second
pass sprays a binder (type of glue) that hardens the powder forming a solid layer.
• Newer technologies make use of UV lights and lasers to harden liquid materials to allow for wider range of use.
Working:-
1. The design is made using CAD
2. The final drawing is exported using specialized SW in a format understandable by the Printer.
3. The printer is set up for printing process to begin.
4. The printing process begins by building up layers (0.1mm thick) until the finished product is achieved. It may take several hours depending on the size of the object and material used.
5. The object is then removed and prepared (excess cutting, curing, cleaning).

Question 25

Speakers and Headphones

Answer 25

It involves passing digital Data through a Digital to Analogue Converter (DAC) and then through an Amplifier before emerging
from a Speaker.
The rate at which the DAC is capable of doing this is known as the sampling rate. Ideally sampling rate should be 44100 sample
rate and if a DAC is a 16bit device that means that it is capable of creating samples each of 16 bits.
If a sound file is to be stored it would require
44100 * 16 (bits per sample) * 2(audio channels Left/Right) = 1,411,200 bits per second of the sound. Therefore, calculating the
size of sound file becomes a relatively straightforward process.

Question 26

LEDs and LCDs

Answer 26

Most monitors and TVs today are made from Liquid Crystal Display/Diodes which means that the front layer of the monitor is made up of liquid crystal diodes in the groups of three (RED, GREEN, BLUE) or four (RED,GREEN,BLUE,YELLOW for more vivid colours). LCD Screens come equipped with a backlight which is a Cold Cathode Fluorescent Lamp (i.e. two fluorescent tubes). As opposed to LCD technology the LED technology makes use of a matrix of tiny LEDs which are on their own light emitting sources (no need for CCFL). Furthermore the newer LED technology has the following advantages over LCD:-
• LED’s do not require warm up period that means they
reach maximum brightness immediately.
• Produce whiter light and more vivid colours
• LED are thinner and require less power to run
• LEDs are more reliable.

Question 27

OLED

Answer 27

LED technology which is essentially made up of organic materials as result of which the screens can be flexible and made into a wide range of shapes. An organic film is sandwiched between two charged electrodes (a metallic cathode and glass anode) that give off light when electric charge is given to it. Essentially the benefits of OLEDs over LCD technology is same as LED. However, OLED also provide the following benefits:-
• OLEDs are essentially plastic that is why they
can be made into large thin sheets
• They have a very large field of view about 170
degrees.

Question 28

DLP

Answer 28

The DLP chip contains millions of micro mirrors (one for each pixel) that are either ON (towards light source) or OFF (away from light source). These mirrors can change state thousands of times a second creating 1024 different shades of grey (a.k.a grey scale image). A bright white LIGHT SOURCE passes through a colour filter separating the white light into R,G,B creating over 16 million different colours. The ON and OFF states of the mirrors are then linked with these colours to produce an coloured image. It can be seen as REVERSE BLACK AND WHITE Photography where the colours are removed from an otherwise coloured image.

Question 29

LCD Projector

Answer 29

Older technology than DLP that involves the following steps:-

1. a powerful light beam emits white light onto chromatic coated mirrors that reflect light back at different wavelength (each corresponding to red, green and blue wavelengths) .
2. These coloured lights are passed through three LCD screens that each show the projected image as millions of grey scale pixels.
3. The Red, Green and Blue versions of the images emerge from the LCD screens which are combined at a prism in the centre producing a full colour image. This image is then passed through a projector lens onto a screen.