Input/ Output devices

Question 1

Barcodes

Answer 1

• A type of light is shone on the barcode
• White spaces reflect light and black bars absorb light
• Converted from analogue to digital
• Digital representation is a duplicate of the analogue
• Simple encoding translates light and dark as 1s and 0s
• These create ASCII character codes for a string

Question 2

Pen Barcode Scanner

Answer 2

• Light source and photo diode are next to each other at a pen tip
• Tip of pen is dragged across all bars at a constant speed
• The photo diode measures light intensity
• Must be in contact with the barcode

Question 3

Laser Barcode Scanner

Answer 3

• Laser beam is the light source

- Laser is reflected off a moving mirror allowing the barcode to be read in many different positions

Question 4

Charge Coupled Device Readers

Answer 4

• Tiny light sensors lined in a row at the head of the reader
• Each sensor reads the intensity of light directly in front of it
• Digital pattern is created by sequentially measuring voltages across each sensor in a row

Question 5

Camera based barcode readers

Answer 5

• Uses a camera and image processing techniques
• Can read bad quality barcodes
• Image processing is carried out by the software

Question 6

Digital Cameras

Answer 6

• Uses a CCD or CMOS sensor comprising of millions of tiny light sensors arranged in a grid
• The shutter opens to allow light in and the image is projected upon the sensor at the back of the lens
• Each sensor measures the brightness of each pixel, and turns light to electricity and stores charge as binary
• The image is greyscale so the sensors are placed under a mosaic of RGB filters that separate different wavelengths
• Processor approximates binary values for the three RGB channels based on the value of neighbouring pixels
• Data is saved to memory card

Question 7

RFID

Answer 7

• Can be read from up to 300m away without line of sight
• Passes data from tag to receiver and vice versa
• Contains small microchip and antenna

Question 8

Active RFID

Answer 8

• Require a battery to actively transmit signals

- Often used track things further away like cars at a toll booth or marathon runners

Question 9

Passive RFID

Answer 9

• Small
• short ranged
• Radio waves from reader supply EM power to the card

Question 10

Laser printers

Answer 10

• Printer generates bitmap image of page using a laser unit and mirror
• Draws a negative reverse image on a negatively charged drum
• Laser causes affected areas to lose charge
• Drum rotates past toner hopper to attract charged toner particles to un-lasered areas
• Particles are transferred to the paper and bonded using pressure and heat