Output Devices

• Barcode Readers:

  ·      Light from a laser is directed at a pattern and a sensor detects the intensity of light that bounces back

  ·      A black bar will absorb more light and be less reflective giving a binary reading of 0

  ·      A white bar will be more reflective with a binary reading of 1
• Barcode readers consist of a ​laser light source​, a ​lens​, ​photodiodes ​and a ​mirror.
• Barcode readers:

  1.      The mirror directs light from the laser onto a printed barcode. 

  2.     The light reflected by the barcode passes through the lens and is focused on the photodiode which ​turns light into electrical charge​  
• Barcodes can have ​error detection​ such as ​parity bits ​and ​check digits​ built in, which allows computers to tell whether a barcode has been read correctly.
• Digital cameras:

  ·      Digital cameras consist of a ​lens ​that focuses light onto a ​sensor​ and a shutter which regulates the path of light between the lens and the sensor.

  ·      Two sensors commonly used in digital cameras are ​CMOS ​(complementary metal oxide semiconductor) and ​CCD (charge coupled device). 
• Digital cameras:

  1. A shutter lets in light onto a sensor
  2. Sensors convert incident light into electrical charge.
  3. Charge builds up in cells, each of which ​represents a pixel ​in the image.
  4. Once the photograph has been taken, the charge in each of the cells is measured ​and converted to a digital value which is then processed by the camera and stored as a digital image.
• Digital camera:

  ·      In colour cameras, there are​ multiple cells for each pixel​, each of which has a ​filter ​that only allows in ​certain wavelengths ​of light. 

  ·      This lets the camera build up a ​separate image for the intensity of ​each colour​ of light which can then be ​combined ​to form a full colour photograph. 
• Digital camera:

  ·      A​ Bayer filter ​is a special colour filter used in digital cameras that has the same number of green filters as red and blue combined.

  ·      Using a Bayer filter produces an image that is a ​closer approximation​ of what the human eye, which is most sensitive to green light. 
• Laser printer:

  • A laser printer is an output device that produces images on paper from digital signals.
  • Laser printers, which print ​whole pages at a time​, consist of a ​laser light source​, ​mirror​, drum​, a​ toner roller​ and ​fusers​
  • Colour printers apply this same process with ​four different colours​ of toner: cyan, yellow, magenta, and black to achieve full colour prints.
• Laser printer:

  1·    The drum is ​positively charged ​all over before the laser is directed at its surface by the mirror.

  2·    Areas on which the laser is incident are ​discharged​, leaving behind an ​impression of the file​ in electrical charge on the drum.

  3·    The toner roller dispenses ​negatively charged toner​ onto the drum. 

  4·    As ​opposite charges attract​, toner is attracted to the positively charged portions of the drum.  

  5·    The toner is then applied to the paper by the drum

  6·    Then the paper is ​heated ​by fusers, fixing the toner to the paper. 
• RFID:

  • Radio Frequency Identification is a method of transferring information ​wirelessly between a ​tag ​and a ​reader​
  • Inside an RFID tag is a ​chip ​which contains a small amount of memory. The chip is attached to a coil of wire which acts as an ​antenna​. 
• RFID:

  • Most RFID tags are ​passive​, meaning that they induce enough power wirelessly from the reader to operate the chip. 
  • However, ​active ​tags (which contain a small power supply like a battery) also exist and can be used much further away from readers than passive tags which must be held within a few centimetres of their reader. 
• RFID:

  1.     When an RFID tag is scanned, the reader emits ​radio waves​ which are picked up by the tag’s antenna

  2.     The power induced in the tag’s antenna from these waves is enough to power the chip 

  3.     which then uses its antenna to emit its own radio wave, which contains the information held on the chip. 

  4.     This wave is picked up by the reader which ​decodes ​the information and returns the information to a computer.