Unit 3.2 - input and output devices Flashcards
What is an input device?
A hardware device used to enter data into a computer system. E.g. keyboards
Keyboard i
- Underneath each key is a small peg. When pressed on, it touches contact layer below which generates electric signal. That is than converted into a unique binary code.
- Use: typing text & numerical data
+ simple to use, efficient & fast data input if trained - easy to make mistakes, can be slow if not trained
Mouse i
- An LED light is reflected off a surface and any movement is detected by group of photosensitive diodes
- Use: controlling cursor
+ simple to use, efficient screen navigation - requires flat surface, reflective/shiny surfaces don’t work, dirt can impair use
2D scanner i
- bright light illuminates document as it is scanned. Mirrors and lenses are used to reflect to reflect the document onto photosensitive diodes. Electrical charges are converted into digital signals.
- use: digitizing printed information
+ creates high quality editable digital copies - require memory, lower quality than original
3D scanner i
- A laser is moved across the object and its dimensions are measured. Afterwards, digital replica is created and can be easily produced using 3d printer
- can take measurement of real life object and create accurate digital model.
+ can fix defects, very accurate - can be slow, poor scan quality of reflective/low contrast objects
Barcode reader i
- Shines LED onto barcodes, which is reflected back. Measures reflected light to read data
- Use: scan items to find price and add to checkout
+ efficient method of entering product info, one scan allows multiple processes - damaged barcodes do not scan, requiring slow manual input
QR code reader i
- same principle as barcode reader, only this time light is reflected off black squares and white background
- use: taking user to website/displaying textual message when scanned
+ efficient way of accessing info, variety of data can be embedded, partial qr codes can still be read - not as universal as barcodes, phone is required
Digital camera i
- uses an image sensor to measure light and take a photo, which is stored digitally on a device such as an SD card.
- use: take photos/videos
+ easy to edit, share and create backups; images can be reviewed immediately - limited memory, image quality varies
3 types of touch screen i
Resistive - two thin sheets of metal over screen. When user applies pressure to screen, metal sheets make contact, completing an electric circuit. This can be used to detect exactly where the user pressed
Capacitive - transparent layer over screen, detects static electrical charge in human body. When user touches screen, this charge is detected as is the touch location
Infra-red - grid of infra-red light over screen. When user touches screen, light beams are broken, which is used to detect the touch location.
Touch screen i
Use: user selecting from small range of options
+ simple to use, combines input and output devices
- less useful if lots of text/numerical data need to be input because it can be imprecise, some types may not work with gloves
Interactive whiteboard
- a projector casts an image onto it. Whiteboard can detect contact with screen and sends each contact point to computer
- use: presenting presentations in an engaging way
+ encourages engagement, doesn’t require external material like chalk - can have remote access issues or projection problems
Microphone
- a diaphragm vibrates when sound waves hit it. These vibrations are detected and turned into electric signals
- use: allows sound input
+ allows disabled users to input vocal commands to computer - may be inaccurate, speech recognition systems must be trained before use
What are output devices?
Devices that take processed data, and show it in a format suitable for humans to understand
Printer (2 types) o
- Inkjet - use ink cartridges to spray tiny droplets of ink at a piece of paper to form an image. + cheaper, better quality color gradation on images - slow
- Laser - user laser to apply static charge to areas on the paper. Powder ink (toner) is then attached to the static charges and sticks to the paper in these areas, forming image. + higher quality text documents, faster - more expensive
Use: create paper/hard copies of documents/images.
Projector (2 types) o
Use: display images and videos on large areas. Good for when multiple people need to see output.
Liquid crystal display - creates image by projecting light in 3 colors: red, blue & green. These colors are combined to form a final image. + higher quality images
Digital light processing - thousands of tiny mirrors are used to reflect a digital image from a computer onto screen. + smaller, more portable
Screen/monitor (2 types) o
Liquid crystal display: crystals are put between 2 sheets of glass. A white back light illuminates the screen from behind. When the crystals are solid, light can’t pass through. When an electrical current is applied to the crystals in individual pixels, light is passed through and an image forms. + low initial cost
Light emitting diode: works similar to LCD, but instead of a fluorescent back light, they use LEDs to generate the light. + better contrast, better quality images, use less electricity = more cost effective in long run
Speaker o
- produces output in the form of sound, by converting electrical signals into vibrations
+ large variety of outputs possible, accessible for visually impaired users - built-in speakers often have poor sound quality
3d printer o
Use: print physical, 3d objects
- build up thin layers of material (plastic), layer by layer until object is complete
+ cheap production of custom made objects, easily shared designs
- slow, expensive initial cost,
Actuator o
- takes a digital signal and outputs it as a physical movement
use: moving, opening, rotating objects
What is a sensor?
An input device that detects and measures changes about the physical environment. The information gathered is sent to a computer.
Sensors do not perform any processing!! They are different from other input devices because they usually work automatically and continuously.
Acoustic sensor
Detects sounds, even outside the human hearing range, and converts detected sounds into digital format.
Use: Burglar alarm to detect break-ins
Accelerometer
Measures the rate of change of velocity.
Use: cars (sudden deceleration to activate emergency pillow), smartphones (e.g. in games where it is controlled by moving the phone itself)
Flow sensor
Measures the flow speed of liquids/gases in pipes.
Use: detect leaks/blockages in pipes (detected by reduced flow speed), check oxygen levels
Gas sensor
Detects presence of gas in industrial or domestic settings
Use: detecting presence of toxic gas in chemical manufacturing plant, drop in oxygen levels in the air, etc/
Humidity sensor
Detects presence water vapor in the air.
Use: environmental control systems, air conditioning. E.g. help a computer determine if environment is correct for plants growing in greenhouse
Infrared (motion) sensor
Detects movement/presence of objects by measuring infrared light reflected from objects. Can also measure changes in levels of heat radiation, therefore detecting presence.
Use: automatic doors, alarm systems
Level sensor
Uses gyroscope to detect if it is being rotated/tilted or detects the levels of liquids, powders, etc.
Uses: phones (controlled by tilting), ice-maker in fridge
Light sensor
Detects light levels/brightness of surrounding light (visible or invisible).
Use: Automatic lighting systems (lamps turning on after natural light falls below certain level), phones, scanners
Magnetic field sensor
Detects changed in the strength and direction of magnetic field.
Uses: gps devices
Moisture sensor
Detects the presence of water/ measures the amount of water in a particular material based on its electrical resistance
Use: farming, greenhouses, detecting wood rot
Ph sensor
Detects how acidic/alkaline a substance is by detecting changes in voltage.
Use: swimming pool, chemical factory
Pressure sensor
Measures the pressure of a gas/liquid or measures the amount of weight pushing down on it, such as a floor plate.
Use: gas pressure in nuclear reactor, tyre pressure, weighing lorries.
Proximity sensor
Detects when an object is close without needing to touch it.
Use: cards (to avoid collisions), robots (to help them navigate)
Temperature sensor
Measures heat energy/the amount of heat generated by an object. Can detect changes to heat produced.
Use: air conditioning/heating, refrigerator, engine management in cars
How do sensors work?
- Input is detected by a sensor
- Input is converted from analogue to digital using an ADC
- Digital data is sent to a microprocessor to be compared to stored values
- Appropriate output is executed based on the system’s requirements
- This process happens in a continuous loop
