computer science - input and output devices

input devices

-hardware device that allows users to enter data or commands into a computer system.
-converts inputs into digital data to be processed

barcode structure

A barcode consists of dark and light parallel lines representing numbers 0 to 9.Guard bars separate left and right sections of the barcode.
Each digit is represented by bars of 1 to 4 blocks thick. Different patterns for digits on the left and right sides.

barcode scanning process

Scanned by a red laser or LED.
Dark areas reflect little light, allowing bars to be read.
Reflected light is read by sensors (photoelectric cells).Laser/LED scans generate patterns converted into digital data for computer understanding.

pros of barcodes for management

Easier price changes.
Better sales information.
Automatic stock control.
Efficient customer buying habit analysis.

pros of barcodes for cutomers

Faster checkout queues.
Reduced charging errors.
Itemized bills.
Potential cost savings.
Improved tracking of "sell by dates."

how does digital camera work

-captures light and converts into digital image
-light enter through lens, it reaches image sensors where it is spilt into millions of pixels (each pixel measures light intensity which is converted into binary)

uses of digital camera

-facial recognitions
-can instantly create an image which can easily be duplicated and transmitted via internet

describe keyboard

-most common text based data input device
-connected by USB or wirelessly
-Each key on a keyboard has a peg underneath it which makes contact with a conducting membrane. This is then converted into an electrical signal to transmit a unique character code

describe microphone

-converts sound waves into electrical signals
-diaphragm vibrates in response to sound waves, these vibrations are converted into electrical signals by coil of wire

describe optical mouse

-use laser to detect and track movement, which is then processed and interpreted as movement on virtual cursor on screen
-reliable due to no moving parts
-used to control graphical user interface

describe QR code scanner

-visual representation of data using black and white squares
-can represent over 7000 digits (barcode = 30)
-scanned by camera and software converts squares to binary

types of touchscreen

-resistive screen
-infra-red screens
-capacitive screens

how do resistive screens work

-two conductive layers
-top = flexible
-when screen is touched the two layers connect, completing a ciruit

pros of resistive screens

+cheap
+resistant to surface contaminants
+responds to finger, gloves, stylus
used in cash machines, medical equipment

how do infra red screens work

-LEDs shine infrared light across a screen forming a matrix. when screen is touched the beams are interrupted

pros of infra red screens

+good image quality
+high precision
+durable
+allow multiple touches at some time
-requires bare finger or stylus
used in tablets, laptops, phones

how do capacitive screens work

-three layers
-protective layer, a transparent conductive layer and a glass substrate
-when touched electrostatic field of conductive layer changes

pros of capacitive screens

+good image quality
+unlimited touch-life
+scale well
-sensitive to interference from light, water, snow
used large scale commercial displays

describe 2D scanners

scanner shines a strip of light over a document. Reflected light is measured for each pixel. This data is converted into binary data so the document can be digitally recreated

describe 3D scanners

scanner shines a light over an object. The geometry and dimensions are recorded so the object can be recreated digitally

output device

allows the user to view or listen to the data a computer processes

actuators

-used together with a motor to translate energy into a movement of a physical object
-eg turning wheel, opening door, moving robots
-used with sensors

types of light projectors

-digital light projector (DLP)
-LCD projector

how does DLP projector work

uses micro-mirrors arranged in a grid on a microprocessor within the projector. light is shone through colour filters and the mirrors
(the position of the mirrors is changed to change light intenstiy)

how does LCD projectors work

use three mirror filters to separate an image into red, green and blue. the three images are then combined to produce the full colour images

pros and cons of DLP

+ higher contrast ratios
+ smooth video
+ more reliable
+ small and light
- images have "shadows" when showing moving image
- colour definitions is not as good

pros and cons of LCD

+ sharper image
+ better colour saturation and intensity
+ less power and less heat
+ quieter
- worse contrast ratio
- limited life
- LCD panels degrade over time

types of printers

-laser printer
-inkjet printer

how do inkjet printers work

-have print head which moves across the page
-spray liquid ink droplets from ink cartridges
-The droplets can be piezoelectric or thermal bubble technology
- Inkjet printers produce high quality hard copies of digital images or documents
-used in homes

how do laser printers work

-very fast when making multiple copies
-used for high volume eg leaflets
-how running cost per page
-Have large toner (dry ink) cartridges and large paper trays
-Use positive and negative charges to make the toner particles stick to piece of paper, heat is then used to bond the particles to the paper

3D printers

-create 3D models by depositing layers of material
-used for rapid prototypes
-allow for precision and can be used in medicine

LCD

Liquid Crystal Display
-made up millions of tiny crystals
-display is made of pixels arranged in matrix
-requires backlighting
-used in TV, monitors, tablets, phones
-low power and cool temperature
-no image burn or flicker issues
-bright images and colours
-cheaper than LED

types of screens

-LCD - liquid crystal display
-LED - light emitting diode screen
-OLED - organic light emitting diode screen

LED

Light Emitting Diode screen
-made up of tiny LEDs
-need no backlighting so thinner and lighter
-LEDs are replacing LCDs
-better image quality and longer life span
-can be used for very large screens
-very little power so can be on for several hours

OLED

organic light emitting diode screen
-much thinner and lighter than LCD
-use organic light emitting diodes
-uses carbon to create semiconductors
-dont need back lighting
-very thin, flexible screens

speakers

-take digital sound and output then as sound waves
-use DAC (digital to analogue converter) to change data into electric signals
-signal is passed through amplifier to create current large enough to allow the loudspeaker to convert it to sound waves

sensors

input devices
-measure physical property of their environment
-can be used for monitoring systems and control systems

monitoring vs control

Monitoring: Observing without system impact.
Control: System adjustments based on sensor data.