External Hardware Devices

External Hardware Devices

1. Barcode Scanner

   • Each digit represented by black bars with white gaps
   • 1. LED scans barcode
   • 2. White reflects the most light, black reflects the least. A photoelectric cell detects the reflected light.
   • 3. The cell generates a pattern of pulses corresponding to the barcode
   • 4. An electronic circuit converts these pulses into binary digits, which are sent to a computer
   • 5. The computer then uses database software to look up the product with the barcode

2. Digital Camera

   • 1. When capture button is pressed, aperture (hole) opens and light streams through the lens
   • 2. A charge-coupled device (CCD) converts light into electrical signals
   • 3. The CCD breaks up the incoming light into millions of pixels
   • 4. The CCD measure the colour and brightness of each pixel and stores it
   • 5. The result is a photo saved as an enormous string of binary describing each pixel
   • Components
     • Flash Capacitor
       • Charges for several seconds for the flash
     • Flash lamp
       • The lamp that produces the flash
     • Lens
       • Focuses incoming light onto CCD
     • Focusing mechanism
       • A switch that changes between focusing for short and long distant shots
     • CCD
       • Light detector
     • Processor Chip
       • Controls the functions of the camera

3. Laser Printers

   • Invented in the 60s by Gary Starkweather
     • Worked for Xerox, who made photocopiers
     • Could print 1 page per second
     • Eventually made into standards, resulting in LaserJet and LaserWriter
   • 1. Data is sent from the computer to the printer
   • 2. An electronic circuit makes sure the format of the document to print is correct
   • 3. This circuit activates the corona wire, which gives everything around it a static charge
   • 4. This charges the photoreceptor drum
   • 5. Simultaneously, the laser draws the image onto the drum (without moving itself, there are moving mirrors)
   • 6. An ink roller coats the drum in postively charged toner which sticks to the negatively charged laser areas
   • 7. Paper moves from a hopper and charged by another corona wire
   • 8. Attracts negative toner particles which rest on the paper
   • 9. Paper is sent through 2 rollers which apply heat and pressure so the toner stays on. Paper sent out the printer.

4. RFID

   • Radio Frequency Identification
   • Made up of a tag, antenna and reader
   • The reader uses electromagnetic fields to identify the emitted radio frequencies emitted from the antenna
     • The tags store data and then the reader sends this data to a computer, such as the tag's location