Input / Output devices Flashcards

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1
Q

How do barcode readers work?

A

They use check digit for validation. If the check digit does not match the calculated value it gives a input error. The validation is embedded into the barcode reader
There is also a code underneath in case barcode cannot be read so can be inputted manually

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2
Q

Principles of operation of a barcode reader

A
  1. Light from laser lights barcode
  2. More light will be reflected from white areas than black
  3. The reflected light is captured by photoelectric cells
  4. These generate a set of electrical pulses, that correlate to black and white striped of barcode. Black bar absorb so give 1. White bar reflect more giving 0
  5. Pulses are processed and converted to binary number to represent the code
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3
Q

What are the 2 common barcode system and what are they used in

A

Universal product code version ‘A’ (UPC-A) / European Article Number (EAN) - Used in retail and warehousing, uses letters and numbers

Code 128 - Used in transport and shipment tracking, uses numeric digits

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4
Q

How do you read UPC-A/EAN system

A

Uses long guard bar to show start and end. Alternates dark and light of varying thickness. Left side manufacturer number. Right side the product number. Check number on the right

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5
Q

How do you read retail barcodes

A

Right hand code inverse of left-hand codes
Left hand have odd number of black bars
Right hand have even

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6
Q

How do digital cameras work

A

When captures an image, it breaks it up through the lens into a grid of pixels
They sense the colour by using RGB filters.

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7
Q

What are the principles of operation for a laser printer

A
  1. Data sent to printer driver
  2. Put into format printer can process
  3. Printer driver checks status to see if can print
  4. Data sent are stored in data buffer
  5. Printer drum is given negative charge
  6. As printer drum rotates laser beam goes across removing charge in certain areas. Positively charged areas match areas to be printed on
  7. Printer drum coated with negatively charged toner, sticking only to positively charged parts of the drum
  8. Positively charged paper rolled over drum
  9. Toner drum sticks to paper printing copy of image
  10. Prevent paper from sticking to drum by removing the charge
  11. Paper goes through fuser boning the ink
  12. At the end discharge lamp removes electrical charge allowing it to be ready for next print.
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8
Q

How does RFID work

A

Allows data to be transmitted wirelessly using radio waves. Uses a transponder and a reader.

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9
Q

Difference between passive and active RFID

A

Passive: Do not contain power supply. Powered by radio energy transmitted by the reader. Antenna collects energy from transmitter to activate chip. Range is 1m, some systems require being really close to tag

Active: Small battery in tag, device transmit identifier at regular intervals. Depending on power supply range can be up to 200m.

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10
Q

Advantages of RFID

A

Using radio signals means system does not require line of sight from tag and reader
Readers can process multiple tags at a time as each have their own unique identifier

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11
Q

Principles of operation of RFID

A
  1. Reader transmit encoded radio signal to interrogate the tag
  2. Tag receives message and responds with identifier and any other stored data
  3. Reader communicates with database to store and evaluate data
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