3.2 Input Output Devices Flashcards
What is an input device
A device that allows data to be entered into a computer system
Describe the operation of a 2D scanner
- Shines light onto the surface of a document
- Refelected light is captured…
- … using mirrors and lenses
- captured image is converted into a digital file
- produces a 2d digital file
Describe the operation of a 3D scanner
- Scanner shine a laser/light over te surface of a 3d object
- records the measurements of the dimensions of the object
- measurements are converted into a digital file
- produces a 3d digital model
Describe the operation of a bar code reader
- Reader shines a light/red laser at barcode
- photoelectric cells detect light reflected back
- white lines reflect more light
- different reflections convert to different binary values
Describe the operation of a QR code reader
Quick Response Code
- QR code is captured by a cmaera
- processed by an app
- data is decoded
- modules are used for alignment
How does a barcode help a supermarket manage stock
- barcode identifies a (unique) product
- barcode can be used to look up product (in a database)
- data about stock levels can be stored on a system
- stock can be automatically deducted from the system
- can check stock is below a certain level // check stock level
- automatic re-order // alerts when stock is low
- automatically update new stock level
- to locate if an item of stock is available in another location
Bar Code vs QR code
Barcode:
- 1d
- uses vertical lines
- some need to be lined up
QR:
- 2d
- uses squares
- more data can be stored
- can be read from any angle
- faster to scan
Both are faster than typing, no human input so less errors
Describe the operation of a digital camera
- Shutter opens and lets light onto the CCD sensor at the back of the lens
- intensity and colour of light is measured by millions of tiny sensors arranged in a grid
- converted to binary values
- stored as an image in the cameras memory
Pros & Cons of a conventional keyboard
Pros: simple and easy to use, potentially faster
Cons: slow if not trained, greater potential for mistakes
Pros & Cons of a concept keyboard
Pros: fewer errors, faster, less training, less vulnerable to dirt/food damage
Cons: not suitable for large amounts of choices, not suitable for all tasks
Describe the operation of mechanical mice
a rubber ball under the mouse moves around on a hard surface and sensors work out the orientation of the mouse
Describe the operation of an optical mouse
Uses a red LED and a sensor to determine the movement of the mouse as it passes of patterns on the surface
Pros & Cons trackball
Pros: little desk space, fine control , can be integrated into a keyboard
Cons: time getting used, expensive
Pros & Cons of touchscreen
Pros: output and input occupy same space, simple and easy to use, works well with icons
Cons: low precision, difficult to use if damaged
Describe how a capacitive touchscreen work
- Made up of many layers of glass that act as a capacitor
- As your finger comes close to a capacitor it changes the local electrostatic field
- Sensors are located around the screen // sensors are used to read the electric field
- The system monitors each capacitor to discover where the finger touched the screen
- Coordinates of touch determined/calculated/measured
Pros & Cons of Capacitive touch screen
Pros: works in sunlight, durable, multi-touch
Cons: glass screen, doesn’t work with gloves
Explain why a capacitive touch screen will not register the touch of a glove
Gloves are not conductive (insulator)
Blocks the charge from a finger
Stops the electrostatic field being changed/disturbed
Describe how a resistive touch screen works
- 2 layers
- flexible plastic surface seperated from a layer of glass coated in conductive material
- separated by tiny spacers
- -when touched the plastic deforms and the 2 conductve films meet
- -Calculation is carried out on where layers are connected
Pros & Cons of a resistive touch screen
Pros: cheap, works with styluses
Cons: scratching, low durability, no multi-touch
Describe how an infrared touch screen works
- The screen has grid of infrared LED beams
- Photocells detect where a beam is broken
- The position of the touch is calculated
Pros & Cons of infrared touch screen
Pros: durable, multi touch, works with gloves
Cons: expensive, objects can trigger a ‘touch’, sensitive to dust/dirt
Pros & Cons of an interactive whiteboard
Pros:
- large display allows multple people to work,
- interactive - helps with presentation,
- text/drawings can be captured for later
Cons:
- requires a board, projector & computer to work
- low precision
- bad in bright light
How do microphones work
- When sound reaches the microphone a diaphragm vibrates back and forth
- the causes the coil to vibrate which changes the magnetic field produced by the magnet
- this produces an electric signal
- this signal goes to a ADC and converted to digial volume
List 8 sensors
- Temperature
- moisture/humidty
- light
- infrared/motion
- acoustic
- gas
- pH
- magnetic field
What is the difference between a moisture sensor and a humidity sensor
Moisture sensor: the amount of moisure in a certain material
Humidty sensor: the amount of moisture in the air
Desribe how sensors and microproccesors are used to monitor a process
- {…} sensor takes a reading
- The reading is converted from analogue to digital using an ADC …
- … and sent to the microproccesor
- The microprocessor compares the value to stored values
- If the value is outside range/matches….
- … the microprocessor sends a signal to {…}
- Monitoring is continuous
What is an output device
A device that allows the user to view/hear data from a computer system
Describe how an inkjet printer prints a document
- rollers are used to move the paper through the printer
- nozzles spray ink onto the paper
- nozzels are moved across the paper
- different coloured inks are mixed to create the colours
- technology can be piezoelectric or thermal bubble
Describe thermal bubble
- Ink is heated
- … and evaporates into a bubble
- The bubble is pushed through the nozzle on to the paper
- … then the bubble collapses
Describe piezoelectric crystal
- Electrical current is applied to a crystal
- …which makes it vibrate
- …which forces a droplet of ink through the nozzle
Pros & Cons of thermal bubble
Pros: cheaper, more print nozzles
Cons: larger droplets, narrow range of inks - high heat, more maintance - high heat
Pros & Cons of piezoelectric crystal
Pros: precise ink drop size, wide range of inks, run for longer
Cons: more expensive, fewer print heads can be used
What is a printer interrupt
- A signal sent from a device/software
- … to the processor. The proccesor stops and services the interrupt
What are printer drivers
Software that converts the data to be printed in a form specific to a given printer
What is a printer buffer
-Temporary memory which stores data until it is readyto be used (printed)
How does a laser printer work
- uses toner (powerdered ink)
- drum is postively charged
- laser reverses the charge on parts of the drum to create an image of the page to be printed
- the positvely charged toner stick to the negatively charged parts of the drum
- the toner is transferred to the paper
- the toner is fused by heated rollers
Pros & Cons of a laser printer
Pros: cheaper per page, faster , text is high quality
Cons: printer is expensive, toner is expensive, low quality images, printer is large in size
Pros & Cons of inkjet printer
Pros: printer is cheap, print on many media types
Cons: frequent ink changes needed, noisy, ink is expensive
What is a 3D printer
An output device used to creat 3D objects from a computer model
The model is often designed using CAD
What is a cutter, 2D vs 3D cutter
Cutters use laser/fire/water to cut wood/plastic/metal
2D: Cuts holes/shapes in a 2D surface, x-y plane
3D: Cuts holes/shapes into a 3D surface, can rotate to cut at many angles, x-y-z plane
How do speakers/headphones work
signal is converted to analogue using a DAC
Voltage differences vibrate a cone in the speaker at different frequences and amplitude to produce a sound
What is an actuator
- An electromechanical device…
- … responsible for moving and controlling a mechanism or system
e. g relay, solenoid, motor
Desribe the operation of an LCD screen
Liquid crystal display
- uses fluorescent lamp as backlighting
- groups of red/green/blue light filters form each pixel
- liquid crystals are manipulated to allow light through the RGB filters
Desribe the operation of an LED screen
Light Emmiting diode
- Uses LED lights as back lighting
- groups of red/green/blue filters form each pixel
- liquid crystals are manipulated to allow light through RGB filters
Benefits of an LED screen
- allows localised dimming
- deeper blacks
- sharper image
- brighter light
Desribe the operation of a LCD projector
- White light is split into red,green,blue by mirrors
- RGB light channels pass through seperate LCD screens…
- …which determine how much red,green,blue is present in the final image
- RGB light is reassembled into a single beam
Desribe the operation of a DLP projector
Digital Light Projector
- A white light passes through colour filters on a rapidly turning spinning wheel
- DLP micro chip has millions of mirros each corresponding to a pixel. They can switch between ‘on’ & ‘off’ to crete shades of grey light
- The coloured light and grey light are combined
- The image is projected
