Input / Output devices

Question 1

How do barcode readers work?

Answer 1

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

Question 2

Principles of operation of a barcode reader

Answer 2

1. Light illuminates the barcode
2. More light reflected from white areas than black bar
3. Reflected light is captured by photoelectric cells that generate a set of electrical pulses. That correspond to black or white stripes
4. Pulses then converted to binary

Question 3

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

Answer 3

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

Question 4

How do you read UPC-A/EAN system

Answer 4

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

Question 5

How do you read retail barcodes

Answer 5

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

Question 6

How do digital cameras work

Answer 6

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

Question 7

What are the principles of operation for a laser printer

Answer 7

1. Negative charge is applied to the drum.
2. A laser beam is directed at the drum.
3. Laser beam is directed using a mirror
4. Negative charge is neutralised where laser strikers
5. Negative charge is applied to the toner
6. Toner sticks to neutralised areas of drum
7. Positively charged transfer roller assists transfer of toner from drum to paper
8. Heat fuses toner onto the paper

Question 8

How does RFID work

Answer 8

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

Question 9

Difference between passive and active RFID

Answer 9

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.

Question 10

Advantages of RFID

Answer 10

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

Question 11

Principles of operation of RFID

Answer 11

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

Question 12

Principles of operation of a digital camera

Answer 12

1. Capture light with array of photosensors
2. Amount of light represents analogue voltages
3. Analogue voltage converted to digital values using a ADC
4. Digital values used to create pixel data
5. Pixel data then represents the colour creating the image