3.2 Input and output devices

##### Two-dimensional Scanners
- Used to input hard-copy documents
- The image is converted into an electronic form which can be stored in the computer
- *Optical Character Recognition (OCR)* is a software which converts scanned documents into a text file format
- If the original document was a photo/image, then the scanned image forms an image file such as JPEG
##### The operation of 2D scanner
  - A light is shone onto the surface of the document
  - The light is moved across the document
  - The reflected light is captured (using mirrors and lenses)
  - The reflections are converted to binary
###### Application of 2D Scanners at an Airport:
- Make use of (OCR) to produce digital images which represent the passport pages
- Text can be stored in ASCII format
- The 2D photograph in the passport is also scanned and stored as jpeg image
- The passenger’s face is also photographed using a digital camera and compared using face recognition software
- Key parts of the face are compared (distance between eyes, width of nose)

##### Three-dimensional Scanners
- 3D scanners can scan solid objects and produce a three-dimensional image
- Scanners take images at several points, x, y and z (lasers, magnetic, white light)
- The scanned images can be used in *Computer Aided Design (CAD)* or to a 3D printer to produce a working model

##### Barcode
- A barcode is a series of dark and light parallel lines of varying thicknesses
- The numbers 0 -9 are each represented by a unique series of lines
- The left and right hand sides of the barcode are separate using guard bars

###### how the barcode is read
- Scanned using a barcode reader and shines (red) laser/light
- Light is reflected back off the barcode; dark areas reflect little light which allows the bars to be read
- Reflected light is read by sensors (photoelectric cells)
- Pattern is generated which is converted to digital

###### how the barcode scanning system operates to check for errors
- A check digit is calculated for the barcode from the barcode data
- using an algorithm (such as Modulo 11)
- and added to the barcode
-  When the barcode is scanned the check digit is recalculated
- A check is performed to see if the check digits match
- If they do not match an error has occurred when scanning the barcode

###### how the barcode system could help the supermarket manage its stock
- The system has a database of stock
- Each product has a (unique) barcode
- Barcode is scanned, and product looked up in database
- Stock levels for product are reduced (by 1)
- Stock is checked against minimum level
- If stock at/below minimum level an order is placed
- When stock is re-ordered flag is reset
##### Quick Response (QR) Codes
- Another type of barcode is the QR codes
- Made up of a matrix of filled in dark squares on a light background
- Can hold more storage (7000 digits)
- Advantages of QR codes:
  - No need for the user to write down website address
  - QR codes can store website addresses

**How is data read from a Quick Response Barcode** 
- The device shines a light/laser onto the QR code
- Corners of code are used to determine position/orientation
- Black and white sections of code reflect light differently
- The device captures the light that is reflected back using sensors
- The light reflections are converted to binary
###### Advantages of QR codes compared to traditional barcodes
- They can hold much more information
- There will be fewer errors; (the higher capacity of the QR code allows the use
of built-in error-checking systems – normal barcodes contain almost no data
redundancy (data which is duplicated) therefore it isn’t possible to guard
against badly printed or damaged barcodes)
- QR codes are easier to read; (they don’t need expensive laser or LED (light
emitting diode) scanners like barcodes – they can be read by the cameras on
smartphones or tablets)
- It is easy to transmit QR codes either as text messages or images
- It is also possible to encrypt QR codes which gives them greater protection
than traditional barcodes.
###### Disadvantages of QR codes compared to traditional barcodes
- More than one QR format is available
- QR codes can be used to transmit malicious codes.(Since
there are a large number of free apps available to a user for generating QR
codes, that means anyone can do this. It is relatively easy to write malicious
code and embed this within the QR code. When the code is scanned, it is
possible the creator of the malicious code could gain access to everything on
the user’s phone (for example, photographs, address book, stored passwords,
and so on). The user could also be sent to a fake website or it is even possible
for a virus to be downloaded.)
##### Digital Cameras
- When pushes the button to take a photograph
- an aperture opens at the front of the camera to allow light to stream in through the Lens. 
- This is captured by a sensor called a Charge-coupled device(convert light into electricity). 
- The Analogue-to-digital converter then converts each Pixel into a digital value.
###### how the captured images are converted to digital photo files
- Image is converted from analogue to digital (using ADC)
- Image is turned into pixels
- Each pixel is given a binary value
- Pixels form a grid (to create the image)
- Each pixel has a colour
- Pixels are stored in sequence (in a file)
- Meta data is stored, It stores the dimensions/colour depth

不考：Charge-coupled device: 
CCD是于1969年由美国[贝尔实验室](https://baike.baidu.com/item/%E8%B4%9D%E5%B0%94%E5%AE%9E%E9%AA%8C%E5%AE%A4/686816?fromModule=lemma_inlink)的[威拉德·博伊尔](https://baike.baidu.com/item/%E5%A8%81%E6%8B%89%E5%BE%B7%C2%B7%E5%8D%9A%E4%BC%8A%E5%B0%94/1143479?fromModule=lemma_inlink)（Willard Sterling Boyle）和乔治·史密斯（George Elwood Smith）所发明的。当时贝尔实验室正在发展[视频电话](https://baike.baidu.com/item/%E8%A7%86%E9%A2%91%E7%94%B5%E8%AF%9D/2673074?fromModule=lemma_inlink)和[半导体](https://baike.baidu.com/item/%E5%8D%8A%E5%AF%BC%E4%BD%93/385669?fromModule=lemma_inlink)气泡式存储器。将这两种新技术结起来后，博伊尔和史密斯得出一种设备，他们命名为“电荷‘气泡’组件”（Charge "Bubble" Devices）。这种设备的特性就是它能沿着一片半导体的表面传递[电荷](https://baike.baidu.com/item/%E7%94%B5%E8%8D%B7/1144574?fromModule=lemma_inlink)，便尝试用来做为记忆设备，当时只能从[寄存器](https://baike.baidu.com/item/%E5%AF%84%E5%AD%98%E5%99%A8/187682?fromModule=lemma_inlink)用“注入”电荷的方式输入记忆。但随即发现[光电效应](https://baike.baidu.com/item/%E5%85%89%E7%94%B5%E6%95%88%E5%BA%94/289208?fromModule=lemma_inlink)能使此种组件表面产生电荷，而组成数字图像。
##### Keyboards
- Connected to computer with a USB connection or by wireless connection
- Each character has an ASCII value and is converted into a digital signal
- Slow method
- Prone to errors

###### how key presses on  keyboard are processed by the computer
- Membrane / matrix / circuit board present at base of keys
- A key is pressed that presses a switch
- When a key is pressed it completes a circuit // changes the current in a circuit
- The location of the keypress is calculated
- An index of characters is searched to find the corresponding keypress
- Each character has an ASCIl / Unicode value
- The ASCIl / Unicode value has a binary value
- Keypress generates an interrupt
- Each character / keypress is added to a buffer to wait to be processed
- The binary can then be processed by the CPU to action the key press

When the user presses a key on a keyboard, the key pushes the ==switch== on the circuit board. This completes a ==circuit==. Signals are sent to the computer that uses the data to calculate which key was pressed.

##### Mouse
Description
- Uses rolling ball / optical sensor / laser to detect motion 
- Movement echoed on screen // moves curser/pointer (on screen)
- Has scroll wheel / Buttons to allow data input

![image.png](https://doc.tiegg.com/media/202603/d1fcd1a8b2234f3e916ff03cfe77cdcf1708.png)
An optical mouse shines an ==LED== from the bottom of the mouse onto a surface. Light bounces straight back from the surface into a ==photoelectric== cell. This has a ==lens== that ==magnifies== the ==reflected== light is converted to a value. This value is transmitted to the computer. The
computer then determines the ==direction== and ==speed== of the movement. When a button on the mouse is clicked, a ==microswitch== is pressed. A ==USB== connection is used to carry the data to the computer.

##### Microphones

- Used to input sound to a computer
- When a microphone picks up sound, a diaphragm vibrates producing an electric signal
- The signal goes to a sound card and is converted into digital values and stored in computer
- *Voice recognition,* voice is detected and converted into digital

###### Voice Recognition

- User’s voice from microphone is converted to digital signals
- Words are translated to wave patterns and computer compares it with already saved ones
- If the patterns match then it means they are from the same person
- Used in security systems e.g. unlocking phone by saying name

##### Speakers

- Sound is produced from a computer by passing the digital data through a Digital toAnalogue Converter (DAC)
- Then through an Amplifier; finally the sound emerges from a Loudspeaker
- Outputs the sound produced by the computer to the user
- Used to listen audios, videos

##### Headphones

- Can give instructions to user with motor disabilities or read text aloud
- Digital sound signals produced by computer passes through a Digital to Analogue Converter
- Then passed through an amplifier to make sound louder
- Output through speakers

##### Touchscreens
###### Capacitive (medium cost tech)
- Made up of many layers of glass and creating electric fields between glass plates in layers
- Sensors are used to read the electric field
- When top layer of glass is touched, electric current changes
- Co-ordinates where the screen was touched is determined by an on-board microprocessor
###### Benefits of Capacitive touchscreens
- Better image clarity than resistive screens, especially in strong sunlight
- Very durable screens that have high scratch resistance
- Projective capacitive screens allow multi-touch.
- more longevity
###### Drawbacks of Capacitive touchscreens
- Surface capacitive screens only work with bare fingers or a special stylus
- They are sensitive to electromagnetic radiation (such as magnetic fields or microwaves).

###### Infra-red *heat* (expensive)
- Use glass as the screen material
- Needs warm object to carry an input operation
###### Infra-red *optical* (expensive)
- (Infrared) rays are sent across screen (from the edges)
- Has sensors around edge // Sensors capture beams
- (Infrared) rays form a grid across the screen
- (Infrared) ray is broken (by a finger blocking a beam)
- Calculation is made (on where beam is broken) to locate the ‘touch’ // Co-ordinates are used to locate the touch
###### Benefits of Infra-red touchscreen
- Allows multi-touch facilities
- Has good screen durability
- The operability isn’t affected by a scratched or cracked screen.
###### Drawbacks of Infra-red touchscreen
- The screen can be sensitive to water or moisture
- It is possible for accidental activation to take place if the infrared beams are disturbed in some way
- Sometimes sensitive to light interference.

###### Resistive (inexpensive)
- Upper layer of polyester, bottom layer of glass
- When the top polyester is touched, the top layer and bottom layer complete a circuit
- causing electricity to flow
- allowing the **co-ordinates/location** of the users touch to be **calculated**|
###### Benefits of resistive touchscreen
- Good resistance to dust and water
- Can be used with bare fingers, stylus and gloved hand.
- Cheap to **manufacture**/**buy**
- Can still be used whilst wearing gloves
- Waterproof // Can be used in bad weather
- Does not easily shatter
- Low power consumption
- (Can) support multitouch
###### Drawbacks of resistive touchscreen
- Low touch sensitivity (sometimes have to press down harder)
- Doesn’t support multi-touch facility
- Poor visibility in strong sunlight
- Vulnerable to scratches on the screen (made of polymer).
- Longevity issues 
- (Normally) lower resolution
- Prone to scratches|
##### Liquid crystal display - LCD
###### what is meant by LCD technology
- Liquid crystal display
- The display is made of pixels arranged in a matrix
- Uses a flat panel display
- Backlit display with LEDs
- Uses light-modulating properties of liquid crystals
- Crystals can be turned between opaque and transparent (to allow light to pass)
- Colours created using RGB
###### Describe how an LCD screen operates to display this data.
- The display is made up of pixels that are arranged together as a matrix
- Each pixel has three filters, red, blue and green
- Shades of colour are achieved by mixing red, blue and green
- The screen is backlit
- Light is shone through the liquid crystals
- The liquid crystals can be made to turn solid or transparent/on or off by changing the shape of the crystal
###### Benefits of LCD
- Low power consumption消耗
- Runs at cool temperature
- Do not suffer image burn 
- Do not suffer flicker闪烁 issues
- Bright image/colours
- High resolution image
- Cheaper to purchase than e.g. LED screen
##### Light emitting diodes (technology) - LED display screen
- The display is made up of pixels that are arranged together as a matrix
- each pixel is formed of three LEDs/filters
- Shades of colour are achieved by mixing red, blue and green
- The screen can be back-lit/edge-lit
- NOTE: Use of liquid crystals with LED technology can also be awarded
###### How the LED screen operates to display
- **Display** made up of pixels that are arranged in a matrix 
- LEDs are behind the screen 
- Light shone at pixels 
- Can have diffuser is used to distribute light evenly 
- RGB filters used and are mixed to create different colours
###### Why we use an LED display screen
- It has a bright screen/colours
- It does not consume much power
- It runs at a cool temperature
- Longevity
- Can operate in cold conditions
- Can be small/compact/thin
###### Benifts of LED
- Brighter更明亮的 colours
- low power consumption
- longevity寿命
- It runs at a cool temperature
- less light strays失散 from beam
- High resolution分辨率
- No flicker闪烁
- Display is thinner
- environmentally friendly
- Fewer pixel failure
- Increased viewing in sunlight
##### Inject printer
###### how the inkjet printer prints an image
- Rollers are used to move the paper through the printer
- Nozzles spray ink onto the paper
- print head are moved across the paper (to distribute the ink)
- Different colour inks are mixed to create required colours

- Technology could be piezoelectric
- Technology could be thermal bubble

(thermal bubble)
- Ink is heated
- and expands/evaporates into a bubble
-  Bubble is pushed through the nozzle on to the paper
- then the bubble collapses

(piezoelectric)
- Electrical current is applied to a crystal
- which makes it vibrate
- which forces a droplet of ink through the nozzle
###### Structure
- A print head which consists of nozzles which spray droplets of ink on to the paper to form characters
- An ink cartridge for each colour (blue, yellow and magenta) and a black cartridge or one single cartridge containing all three colours+black
- A stepper motor and belt which moves the print head assembly across the page from side to side
- A paper feed which automatically feeds the printer with pages as they are required
###### Benefit of inject printer
- Printing may be higher quality
- Can use larger paper sizes
- Can print onto different media
- No warm-up time
###### Drawbacks of inject printer
- Printing will be slower
- Ink is more expensive per page
- Ink can be smeared // ink is not smudge proof
###### Application
- (small quantities of) documents
- photographs
##### Laser printer
- uses powdered ink/toner cartridges
- uses a (charged) printing drum
- makes use of static electricity charges
- uses a fuser to fix/melt ink onto the paper
- uses a discharge lamp to remove static charge from the drum
- useful for high volume (high quality) output, e.g. leaflets
**How a document is printed using a Laser Printer** 
- The printer driver ensures that the data is in a format that the laser printer can understand
- Data is then sent to the laser printer and stored temporarily in the printer buffer
- Has no moving head and uses static charge
- The printing drum is given a positive charge
- As the printing drum rotates, a laser scans across it-this removes the positive charge in certain areas
- Negatively-charged areas are then produced on the printing drums
- these match exactly with the text and images to be printed
- The printing drum is coated in positively-charged toner
- This then sticks to the negatively-charged parts of the printing drum
- A negatively-charged sheet of paper is then rolled over the printing drum
- The toner on the printing drum is now transferred to the paper-to reproduce the required text and images
- The paper goes through a fuser which melts the toner so it fixes permanently to the paper
###### Benefits of laser printer
- Faster speed of printing
- Can print duplex / on both sides
- Many letters can be printed from one toner cartridge
- Can print in high volumes
###### Drawback of laser printer
- Toner cartridge more expensive to buy
- More time to warm-up
- Larger footprint
##### 3D PRINTER
- produces solid, 3D objects/prototypes
- used in CAD/CAM
- makes use of tomography/slices of an object
- The solid object is built up layer by layer 
- uses resin, powdered metal, paper, plastic…

**How a document is printed using a 3D Printer** 
- 3D object of the file is made that needs to be printed made in Auto CAD
- one of the methods to print uses Selective Laser Sintering (SLS)
- uses a laser to fuse small particles of plastic/metal/ceramic-into masses that has the desired three dimensional shape
- the laser then fuses the powdered material selectively
- A new layer of particles is spread out
- The next slice of design part is hardened and joined to the first
- then a new layer is applied on top of it and the process is repeated
- until the object is completed and is sandblasted
###### Application
- (physical) prototype (from CAD)
- (physical) model (from a blueprint)
##### 3D cutter
- Design is created on the computer / software / CAD
- Material is loaded to cutter
- Different types of material can be used
- Uses lasers to cut material
- that use infra-red
- that produces extreme heat
- that is focussed using a special lens
- Can work on both the x,y and z axis
##### Digital Light Projector (DLP)
- **Uses a bright white light source and millions of micro mirrors on a chip**
- **To produce an image to be shone onto a wall or screen**
- The number of micro mirrors decide the resolution of an image
- Bright white light passes through a color filter before it reaches the DLP chip
- It’s split into RGB colors from which a 16 million color combinations possible
- When a micro mirror tilts towards the light source, they are on
- When a micro mirror tilts away from the light source, they are off
- The on and off states of each micro mirror are linked with colours from the filter to produce the coloured image
##### LCD Projector
- White light propelled from the LED inside the projector
- Light reflected at different wavelengths by mirrors
- Those wavelengths represent RGB colors
- The 3 color components pass through 3 LCD screens
- Using these colors, grey images are converted into RGB colors
- Images then combined through a prism to produce full color image
- Colored image projected onto the screen

###### The benefits of LCD projector than DLP projector
- More visible pixels // higher resolution
- Higher colour contrast (in ambient lighting) // more vivid colours
- Colours are (often) more accurate
- Image (usually) appears brighter (with same wattage)
- Will be stationary so does not need the portability of DLP
- Does not need the compactness of DLP
- Cost of purchase (usually) less
- Run quieter
- Any surface can be used as a display
- Uses less power
- Produces less heat
- Does not give the rainbow effect DLP often gives
- Longer lasting lamps
##### Sensors
- Devices that read or measure physical properties
- Data needs to be converted to digital
- *Analogue-to-digital converter (ADC)* converts physical values into digital
- Sensors and their purposes:
  - Acoustic - These sensors act like a microphone that converts sound to electric pulses.
  - Accelerometer - These sensors measure an object's acceleration or deceleration and motion.
  - Flow - This sensor measures the flow of liquid or gas.
  - Gas - These sensors measure the amount/level of any gas in the environment.
  - Humidity - This sensor measures the water vapour in the air or any sample.
  - Infra-red (active) - This IR sensor uses an invisible infrared beam. When the beam is broken/disturbed, it changes the amount of infrared light reaching the detector.
  - Infra-red (passive) - These sensors detect the heat emitted by any type of object.
  - Level - This sensor detects the solids, liquids, or gas level.
  - Light - These devices use light-sensitive cells that generate electric current based on light brightness.
  - Magnetic field - This sensor detects the change in magnetic field.
  - Moisture - This type of sensor detects the water content wherever this sensor has been installed.
  - pH - This measures the acidity or alkalinity.
  - Pressure - This sensor measures the pressure applied
  - Proximity - This sensor detects the nearby objects around the sensor
  - Temperature - These sensors measure the temperature of the environment.
- (Note: You do not need to know the working principle of the sensor. But have an idea of their purposes.)

Examples:
Acoustic
to monitor whether a water pipe has cracked and is leaking and dripping onto the floor
Temperature
- Checking whether the water in a kettle is boiling
- Monitoring the temperature in a room that is climate controlled
Humidity
- Checking whether the air is dry enough in a spray-painting garage
- Checking whether the air is moist enough in a greenhouse
Infra-red
- Detecting motion in a room for a security system
- Detecting whether a person is approaching automatic doors
Magnetic field
- Counting vehicles that cross a bridge
- Monitoring vehicles that enter a car park
###### Control of Street Lighting
- The light sensor sends data to the ADC
- Digitised data and sends it to the microprocessor
- Microprocessor samples data every minute
- If data from sensor < value stored in memory:
  - Signal sent from microprocessor to street lamp
  - Lamp switched on
##### Actuator
- Operated by signals to cause a physical movement
- Controls the movement of a machine