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/down/under 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

##### 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.
![image.png](https://doc.tiegg.com/media/202505/977bb1d19e56410393fb726b0f08601d9055.png)

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

- 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

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
###### Benifts of LED
- Energy efficient // low power consumption
- Long lasting持久 // longevity寿命
- Focussed beam // less light strays失散 from beam
- Brighter更明亮的/vivid鲜明的 colours
- High resolution分辨率
- No flicker闪烁
- Display is thinner
- environmentally friendly
- Fewer pixel failure
- Increased viewing in sunlight
##### Inject printer
- Uses either thermal bubble or piezoelectric technology to produce a hard copy
- Use hundreds of tiny guns to propel ink droplets on paper
- Characters printed are made up of drops of ink-Ink tank supplies ink to an ink dispenser
- Drop of ink from the tank stays at the end of dispenser tube
- When a droplet is to be propelled, circuit energizes the piezoelectric crystal
- Crystal is pushed against a membrane which pushes it to the outlet of ink dispenser
- Droplet comes out from the dispenser onto the paper
###### 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
##### Laser printer
**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
- They can produce solid objects which actually work
- The solid object is built up layer by layer using materials such as powdered resin, powderedmetal, paper or ceramic powder

**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
##### 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