3.2 Input & Output Devices
Input Devices
Input devices convert real-world inputs into digital data which can be processed by a microprocessor.
Barcode Scanner
Shines a red laser at the barcode to read the data
The light from the white lines is reflected back but black lines absorb the light
The different levels of reflection are converted into a binary value
Used for identifying or tracking a product
Some benefits include, faster checkouts, automated stock control, less chance of error, more detailed tracking information
Sample answer:
Device shines a laser at the barcode The white areas reflect the light while the black absorbs light The device reads the reflected light using sensors The reflected light is converted into binary
Digital Camera
Works by capturing light and converting it into a digital image
Light enters through the lens and reaches the image sensor
Each pixel measures light intensity which is converted into binary
Some benefits include, you see a preview of the image, the image can instantly be duplicated, and software can be used to edit digital photos
Keyboard
Text-based data input
Each key has a peg underneath which makes contact with a conducting membrane
This is converted into an electrical signal to transmit a unique character code
Sample answer:
Membrane with circuit board present at the base of the keys When a key is pressed, this presses a switch This completes a circuit The location of the keypress is calculated An index of characters is searched to find which key was pressed Each character has a Unicode value which is then converted into binary This is then processed by the CPU to action the keypress
Microphone
Converts sound waves into electrical signals
Capture real world sound and convert it into digital data using an *
Has a diaphragm that vibrates in response to sound waves
Vibrations are converted into electrical signals by a coil of wire attached to the back of the diaphragm
* Analogue data is non-discrete and digital data is discrete, so non-discrete data is being converted into discrete data. (Note: this may come up as an exam question)
Optical Mouse
Uses a laser to detect and track movement (replicates on-screen)
Used to control the cursor in GUIs
Reliable due to no moving parts
QR Code Scanner
A QR code is a visual representation of data using black and white squares
Can represent over 7000 digits (barcode is 30)
Scanned by a camera
Software converts the squares into binary
Sample answer:
Device shines a laser at the QR code The corners are used to determine position or orientation The white areas reflect the light while the black absorbs light The device reads the reflected light using sensors The reflected light is converted into binary A link or URL is stored within the QR code
Touchscreen
Resistive screen
These consist of two conductive layers. The top layer is flexible. When the screen is touches, the two layers connect, completing a circuit.
Infra-red screen
LEDs shine infrared light across a screen forming a matrix. When the screen is touches, the beams are interrupted.
Capacitive screen
These are made up of a protective layer, a transparent conductive layer, and a glass substrate. Touching the screen changes the electrostatic field of the conductive layer.
Resistive
Cash machines Medical equipment Information kiosk
Cheap to produce Resistant to surface contaminants Can be activated with every object
Infra-red
Tablets Laptops Phones
Excellent image quality High precision and durable Allows for multiple touches at the same time Requires a bare finger or stylus for activation
Capacitive
Commercial displays Medial equipment Information kiosk
Excellent image quality Unlimited touch-life Scale well Sensitive to interference (light, water, snow)
2D & 3D Scanners
2D -> flatbed shines a strip of light over a document, reflected light is measured for each pixel, data is converted into binary so document can be digitally recreated.
Some uses are scanning documents or reading passports
3D -> shines a light over an object, geometry and dimensions are recorded so object can be recreated digitally.
3D model can be modified using software
Can be used to create 3D models with CAD
Some uses are dentistry, product development
Output Devices
A device shows the results of the processing in a way humans can understand (using a screen).
Actuators
Used with a motor to translate energy into real-world movement of a physical object
Often used with sensors, the input of the sensor is checked against stored values
Light Projectors
Project computer outputs onto a large screen
DLP (Digital Light Processing) projectors use millions of micromirrors arranged in a grid. Light is shone through the colour filters and mirrors. The position of the mirrors can be altered to change the intensity of the light.
LCD (Liquid Crystal Display) projectors use three mirror filters to separate an image in to RGB wavelengths. The three images are then combined to produce the full colour image.
DLP
Higher contrast ratios Smooth video Higher reliability Smaller & lighter Better suited to dusty atmospheres
Image suffers from shadows No grey components in the image Colour definition is not as good as LCD
LCD
Sharper image Better colour saturation & intensity Use less power, less heat Quieter to run
Contrast ratios not as good as DLP Have a limited life Panels degrade over time
Laser & Inkjet Printers
Both types create hard copies of a digital document.
Laser Printers
Very fast when making multiple copies
Useful for high volume print jobs
Have a low running cost per page
Often used in business or education
Have large toner (dry ink) and large paper trays
Use positive & negative charges to make the toner particles stick to the paper, heat is used to bond the particles to the paper
Inkjet Printers
A print head moves across the page
Spray liquid ink droplets from ink cartridges onto the paper
Droplets can be piezoelectric or thermal bubble technology
Produce high quality hard copies
3D Printers
Create 3D models by depositing material on top on one another (plastic or resin)
Allows for precision (used in medicine to create prosthetics)
Can be used to create rapid prototypes
Models can be transmitted digitally and then printed
LCD Screens
Millions of tiny liquid crystals
Made of pixels arranged in a matrix
Display requires backlighting
Used for TVs, monitors, phones
Low power consumption, no heat
Do not suffer from image burn or flicker issues
Provide bright images and colours
Cheap to produce than LED screens
LED Screens
Made of tiny LEDs
Do not need backlighting (thinner and lighter)
Better image quality and longer life
Can be used to create very large screens
Consume very little power
Sample answer:
Display is made up of different pixels that are arranged in a matrix LEDs are behind the screen Light is shone at the pixels through a diffuser to distribute the light evenly RGB filters are used and mixed to create different colours
OLED Screens
Much thinner and lighter than LCD screens
Use Organic Light Emitting Diodes
Use organic carbon compound to create semi-conductors
Very thin, flexible screens
Speakers
Used for digital sounds or recordings and output them as sound waves
Digital data is changed into an electric current (ADC)
Passed through an amplifier to create a large current
Loudspeaker converts current into a sound wave
Sensors
These measure a physical property of their environment. They can be used to monitoring and control systems.
Acoustic
Sound
Detect sound changes in machinery Monitor noise pollution Security system
Accelerometer
Acceleration Tilt Vibration
Sudden changes in vehicle movement Detect orientation of device
Flow
Rate of gas / liquid flow
Detect changes in water flow of pipes
Gas
Presence of a gas
Levels of gas in confined spaces When fixing gas leaks
Humidity
Water vapour
Greenhouses
Infra-red
Motion Heat source
Security systems detect intruders Emergency services to detect people
Level
Liquid
Petrol in a car Water in a tank
Light
Light
Headlights
Magnetic field
Presence & strength
Anti-lock braking system
Moisture
Moisture
Soil and buildings
pH
Acidity Alkaline
Soil Chemical processes
Pressure
Gas / liquid
Tyre pressure Pipes
Proximity
Distance
Robotics Safety systems
Temperature
Temperature
Swimming pools Chemical processes
Exam Questions
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