CH 05: Input and Output Devices

Input Devices:

Scanners

• can be two-dimensional (2D) or three-dimensional (3D)’

@@Two-Dimensional Scanners@@

• most common form of scanners
  • generally used to input hard-copy documents
  • convert images to an electronic form that can be stored in a computer

• Optical Character Recognition (OCR): computer software that allows scanned text from the document to be converted into a TEXT FILE FORMAT
• JPEG: scanned format of photograph or image

@@Applications of 2D Scanners at an Airport@@

• used to scan two-dimensional photographs in a passport and stored as JPEG
  • a digital camera is used to photograph a passenger’s face and is stored as an image
  • the two digital images are then compared using face recognition software

• 2D scanners can also be used to read passports and manipulate digital images
• OCR Technology can be used to manipulate digital images and store digital texts in ASCII format

@@Three-Dimensional Scanners@@

• scans and produces three-dimensional images of solid objects
  • takes images at several points along three coordinates (x, y, z)
  • Scanned images can be used in Computer-Aided Design (CAD) or sent to a 3D Printer to produce a physical model
  • Technologies used in 3D scanners: lasers, magnetic resonance, white light, etc.

@@Application of 3D Scanning - Computed Tomographic (CT) Scanners@@

• Computed Tomographic (CT) Scanners: used to create a 3D image of a solid object
• Tomography Technology: builds an image through a series of very thin 2D “slices” that, when put together, represent the 3D solid object.
  • Each “slice” is built up by use of X-rays, radio frequencies, or gamma imaging

• The type of Tomographic Scanner depends on how the image is formed:

Barcode readers/scanners

• series of dark and light parallel lines of varying thickness
  • lines represent numbers 0 to 9
• Universal Product Code (UPC) Version A: adopts different codes for digits appearing on the left and digits appearing on the right
  • left and right digits are separated by guard bars

• digits representation in barcode

• barcode with number 543052:

• Barcode Process:

1. Barcode is read by a red laser or red LED (Light Emitting Diode)
2. Reflects dark and light areas and a pattern is generated
3. Light and Dark pattern (L & D) equivalent to binary is ‘0’ and ‘1’ respectively

     Example:

     “L D D D D D L D” = “0 1 1 1 1 1 0 1”

$Barcode Scanners in Supermarkets$

• Key Field: uniquely identifies each stock item
• Point of Sale Terminal (POS): where price and other item details are sent back
• Advantages of using barcodes to management:
  • easier and faster change prices on stock items
  • more up-to-date information/sales trends
  • reduces time and cost
  • automatic stock control
• Advantages of using barcodes to customers:
  • faster checkout queues
  • reduced errors in charging customers
  • itemized bills
  • better track of “sell by dates”

Quick response (QR) code readers

• another type of barcode
  • made up of a matrix made of filled-in dark squares on light background
  • normal barcodes can hold 30 digits; QR codes can hold over 7000 digits
  • can be scanned anywhere by modern smartphone cameras

• Advantages of QR codes:
  • no need to write down website address
  • can store website addresses/URLs

Digital cameras

• does not require films to record photos
  • can be connected to a computer system via USB port or by Bluetooth

• Camera microprocessors can automatically carry out the following task:
  • adjust shutter speed
  • focus image automatically
  • operate the flash automatically
  • adjust the aperture size
  • adjust the size of the image
  • remove ‘red eye’ when the flash has been used
• Size of photograph file is dependent on the number of pixels

  Example:

• A 14-megapixel camera will need 42 megabytes to store each raw (uncompressed)
  • Quality of photograph depends on: type of lens used, and lighting

Keyboards

• most common method used for data entry
  • used as an input device on computers, tablets, mobile phones, and other electronic items
  • is connected to the computer via USB or wireless connection
  • tablets and mobile phones used Virtual or Touchscreen keyboard technology

• Repetitive Strain Injury (RSI): injury in the hands and wrists caused by frequent use of keyboards
• Ergonomic Keyboards: can help to overcome RSI

Pointing devices (mouse)

• used to select icons on an application. Devices include: mouse, trackerball
  • connected via USB or wireless connection
  • modern type of pointing devices uses red LEDs to detect movement in the x-y direction (Optical Mouse)

• Trackerballs are often used in industrial environments with minimal desk space
• Optical or Analog mice are used in typical computer applications with desk space
• Touchpad: a type of pointing device integrated into portable laptop computers
  • contains a tactile sensor that allows user control by touch

Microphones

• are used to input sound into a computer
• either built into the computer or are external devices connected through USB port or wireless connection
• used in:
  • doing ‘voice-over’ in a presentation
  • speech recognition system
  • voice recognition system
  • enabling a disabled person to communicate

• Voice Recognition: detected voice of user is converted into digital.
  • software compares detected wave pattern to stored wave patterns in memory for match.
  • only certain key phrases can be recognized
• Speech Recognition: a different and more complex technology
  • spoken words are recognized and shown on screen
  • computer will convert sound wave into digital form
• Phenomes: smallest elements that make up a language
  • phenomes are compared with words found in the built-dictionary:

Touchscreens

• most common form of input devices
  • carry out multiple functions using simple touch
  • mainly used in mobile phones
• Three major types of touchscreen technology:

Sensors

• Devices that read or measure physical properties (temperature, pressure, acidity, etc.)
• Analogue: constantly changing values
• Analogue to Digital Converter (ADC): converts physical values into discrete digital values

• Digital Analogue Converter (DAC): used by the computer to control devices by converting digital signals to analogue
• Actuator: an electromechanical device such as a relay, solenoid, or motor
• Different types of sensors and its application:

• Classification of Sensors (Monitoring and Control Systems):

@@Monitoring Applications@@

• Burglar Alarm System:

1. Infra-red sensors pick up movements of intruders
2. Acoustic sensors pick up footstep sounds or glass breaking
3. Pressure sensors pick up the intruder’s weight from the doorway
4. All signals are sent to the computer microprocessor and activate siren or lights when incoming data are outside the acceptable range

@@Control Applications@@

• Street Light

1. Light sensors send signals to the ADC interface
2. ADC converts signals to data and is sent to the Microprocessor
3. The microprocessor evaluates the signals and turns the street lamps on or off depending on the given data

Interactive Whiteboards

• Devices that allow computer images to be displayed on a whiteboard using a digital projector
  • allows users to write on the whiteboard
  • information written and copied on the whiteboard can be stored for later use
  • Example of a whiteboard:

Output Devices:

Paper Printers

@@Inkjet Printers@@

• Inkjet printers are made up of:
  • Print Head: consists of nozzles that spray droplets of ink onto paper
  • Ink Cartridges: stores different colors of ink
  • Stepper Motor and Belt: moves the print head across the page
  • Paper Feed: automatically feeds paper into the printer

• Thermal Bubble: utilizes localized heat which vaporizes ink causing the ink to form tiny bubbles
• Piezoelectric: a tiny electrical charge is given to a crystal located at the back of the ink reservoir for each nozzle. This creates vibrations that force ink to be ejected onto the paper
• Inkjet Printing Process

1. Document data is sent to a printer driver
2. Printer driver checks format of paper and if chosen printer is available
3. Data is sent to the printer and stored in a printer buffer
4. Sensors check if paper is available in the feed tray
5. Print head moves from side to side across paper to print document
6. Once done, the paper is advanced to the output tray
7. Whole process is repeated until there is no more data in printer buffer

@@Laser Printers@@

• makes use of properties of static electricity to produce text and images
  • uses dry powder ink rather than liquid ink
  • can print whole pages in one go
  • doesn’t run out of ink halfway through the print

• Laser Printing Process

1. Document data is sent to a printer driver
2. Printer driver checks format of paper and if chosen printer is available
3. Data is sent to the printer and stored in a printer buffer
4. Sensors check if paper is available in the feed tray
5. Print drum is given positve charge
6. Drum rotates while a laser beam removes positive charges in certain areas leaving negatively charged areas matching the document or image
7. The drum is coated with postively charged Toner (powedered ink)
8. Negatively charged paper is rolled over the drum and the toner sticks to the surfaces
9. Electric charge on paper is removed after one rotation of the drum
   10. Paper goes through a fuser heating and melting the ink
   11. Discharge lamp removes all electric charge from drum

@@Applications of Inkjet and Laser Printers@@

• Inkjet Printers
  • One-off photos
  • Best for colored printing
  • Low quantity-High quality print
• Laser Printers
  • high volume printing
  • posters and flyers
  • monochrome printing

3D printers

• primarily used in Computer-Aided Design (CAD) applications
  • Additive Manufacturing: builds up a solid object layer by layer using powdered resins, metal, paper, or ceramic powder
  • Subtractive Manufacturing: removal of material to make an object

• Two types of 3D printing:
  • Direct 3D printing: uses inkjet technology; the print head can move left to right, up and down.
  • Binder 3D printing: uses two passes for each of the layers; the first pass sprays dry powder while the second pass a binder is sprayed to form a solid layer

@@3D Printing Process@@

1. Design is made using CAD software
2. Design is converted to 3D printer format
3. Solid object is built up through additive manufacturing
4. Object is removed from the printer

@@Uses of 3D Printing@@

• Prosthetic Limbs
• Reconstructive Surgery
• Aerospace Manufacturing
• Fashion and Art
• Vintage Car Parts

2D/3D cutters

• Three-dimensional (3D) laser cutters can recognize an object in the x-y-z direction
• Two-dimensional (2D) laser cutters can only recognize an object in the x-y direction
• 3D laser cutters can cut the following materials:
  • glass
  • crystal
  • metal
  • polymer
  • wood

Actuators

• used in many control applications involving sensors and devices such as ADC and DAC

Loudspeakers

• Sound is produced from a computer by passing the digital data through a Digital Analogue Converter (DAC) and then through an Amplifier; finally the sound emerges from a (loud) Speaker.

• Sampling Rate: rate at which the DAC can translate the digital output into analogue voltages
  • 1 byte = 8bits

LCD/LED monitors

• Liquid Crystal Display/Diode (LCD): front layer of monitor is made up of liquid crystal diodes
  • Pixels (Picture Elements): tiny diodes grouped together in threes or fours
• Cold Cathode Fluorescent Lamp (CCFL): used as a backlighting method for LCDs before LEDs
  • uses two fluorescent tubes behind LCD screen
• Light Emitting Diode (LED): used as a backlighting method for modern LCDs
• Advantages of LED:
  • reaches max brightness almost immediately
  • gives whiter light
  • brighter light improving colour definition
  • thinner monitors using LED technology
  • lasts almost indefinitely
  • consumes very little power
• Organic Light Emitting Diodes (OLED): uses organic compound to create semi-conductors which are very flexible
  • organic films are sandwiched between two charged electrodes (Cathode and Anode)
  • no longer uses LCD technology; OLED is self-contained system
• Advantages of OLED:
  • thinner, lighter, and more flexible displays
  • can be made from plastic rather than glass
  • gives brighter light than LEDs
  • do not require backlighting methods
  • uses much less power than LCDs
  • can be made into large thin sheets
  • very large field of view (170 degrees)

Projectors (LCD and DLP)

• used to project computer output onto larger screens or even onto interactive whiteboards
  • often used in presentations or in multimedia applications

@@Digital Light Projector (DLP)@@

• uses millions of micromirrors on a small DLP chip
  • number of micromirrors and their arrangements determines the resolution of the digital image
  • Micromirrors tilt towards the light source means they are ON; Micromirrors tilt away from light source means they are OFF
• can produce 1024 grey shades

@@LCD Projectors@@

• older technology than DLP
  • A bulb generates a powerful beam of white light from inside the projector body
  • The beam of light is sent to a group of chromatic-coated mirrors that reflects light back at different wavelengths (red, green, and blue)
  • These wavelengths pass through three LCD screens that show images
  • The images are combined using a special prism to produce full color images
  • The image passes through the projector lens onto a screen