External Hardware devices

• How do Barcode Readers work?

  Consist of a laser (light source) , photodiode , mirror , lens

  • mirror directs light shun from laser onto barcode
  • reflected light is incident on photodiode (CCD sensor) after passing through the lens
  • Converted to electrical charge which can be measured and produced digitally & software interpreted
  • Light and dark spots are corresponded to 1s and 0s via different voltages from different intensities of incident light
• 1D (LINEAR) BARCODES

  • hold limited information
  • used for goods
  • use UPC (universal product code) - black and white lines
• 2D (QR) BARCODE

  • greater range of / complex information
  • picked up by smartphone scanners - more accessible
  • linked to URL’s
• Laser Printer

  Laser light source, mirror , drum , toner roller, fuser

  • Drum is coated with negative static charge
  • Laser directed at drum surface through mirror to generate bitmap
  • Surface is discharged wherever laser is incident
  • Toner roller dispenses opposite charge toner onto drum - attracted to negative portions of drum
  • Toner is applied to paper
  • Fusers heat paper to fix/fuse toner to paper
• Digital Camera

  Lens that focuses light onto a sensor and represents it in digital form

  • Shutter is opened and light is let in
  • Lens focuses it onto CCD or CMOS sensor
  • sensor converts incident light into electrical charge
  • built up charge in a cell corresponds to a pixel
  • charge in each cell is measured and converted into a digital value
  • processed and stored digitally
• Colours in Cameras

  Either:

  1. Multiple cells are used per pixel, each covered by RGB filters which combine intensity of each wavelength of light
  2. software approximations from an RGB mosaic
• RFID

  Transfers information wirelessly using radio waves.

  • Once chip is scanned, reader/receiver emits radio waves which are picked up by tags/transmitters antenna.
  • Radio waves energy powers the chip, therefore emitting the information stored through its antenna
  • Receiver picks up waves and are decoded and returned to a computer
• Hard Disk Drives (HDD)

  Most common type of storage device

  • circular magnetic discs (platters) each with an articulating arm
  • The articulating arm moves the read/write head, which changes magnetic polarity of the platters , to access all areas of it
  • Data is written into concentric tracks
  • rotations happen thousands of times per minute
  • More platters & less tracks = more storage , same size
• Solid State Drives (SSD)

  consist of NAND flash memory cells & a controller.

  Data is stored on pages , which are grouped as blocks.

  • Non-volatile
  • memory cells consist of floating gate transistors
  • trap electrical charge
  • controller has to erase info before new info can be written (cannot overwrite)