SLR 18

Input/ Output Devices (I/O Devices): 

Barcode Reader 

• Used for identification 

  • Shops 

  • Tickets/ boarding passes 

  • Passenger luggage 

  • Medical samples and products 

  • Recipes 

  • Libraries 

  • Parcels 

  • Hyperlinks 

  • Map information 

  • Accessing websites and apps 

  • Make payments 

• QR (Quick Response) Codes(2D) and Linear Barcodes(1D) 

• QR Codes store more information than a Linear Barcode 

  Types of barcode reader: 

• Pen-type readers – require a light source and photo diode located next to each other at the tip 

  • Measures light intensity of the light reflected – generates a waveform – light is reflected better on white than black 

  • Dragged across at an even speed  

  • Used when a barcode is handheld – e.g. books 

  • Can take longer, especially for a long barcode and if the speed is not right 

  • Barcode must be clear – not covered in dust or the reader can be damaged 

• Laser reader – uses a laser beam

  • Laser is reflected off a moving mirror – barcode can be read in multiple positions 

  • Shops, self-checkouts 

  • Doesn't need a specific speed 

  • Can be used on a non-linear surface 

  • More robust – nor damaged by dust or water 

  • Need a lot of equipment – not as portable – scanner can’t move – more difficult to fix

  • More expensive 

• CCD – charged coupled device 

  • A row of many light sensors 

  • Measures light intensity 

  • Voltage pattern is recorded 

  • Limited by cable 

• Handheld – not affected by shaking hands – easier to hold 

  • Must be held somewhat horizontally 

  • Can be used on rounded surfaces 

• Camera based – imaging scanner which uses camera and image processing 

  • Can be used on any surface, including screens 

  • Software does most of the work 

  • Easily accessible 

  • Can run out of charge 

  • Not used for linear barcodes 

DSLR Camera 

• Uses CCD or CMOS (complementary metal oxide semi-conductors) - millions of tiny light sensors in a grid 

• Shutter opens, light enters and projects the image onto photosites at the back of the lens 

• Photosites measure the brightness of each pixel – the light becomes electricity and stores the charge as binary 

• Photosites are placed under a Bayer filter to separate wavelengths 

RFID 

• Radio Frequency Identification 

• Needs a tag and a reader 

• Uses radio signals so no need for line of sight 

• Tag contains a chip and antenna – chip is in the middle 

• Antenna sends/ receives signals and chip processes 

• Each tag has a unique identifier and a non-volatile memory cell storing additional data 

• Reader transmits an encoded radio signal 

• Tag will respond to the signal with the identifier 

  Types of RFID tag: 

• Passive 

• Does not have power 

• Reader gives power via radio energy 

• Tag must be very close to the reader 

• Active 

• Has a small battery so has power 

• Tag transmits identifier at regular intervals 

• Vastly increases the distance the tag can be read from 

Laser Printer 

• Bitmap image of the page is created 

• A negative charge is applied to the print drum 

• A laser with a mirror is used on areas of the drum to lose that charge, creating a reverse image of the drum 

• Drum continues to rotate, and is exposed to a positively charged toner, which is attracted to the negatively charged areas on the drum 

• A sheet of paper is passed under the drum and the toner is transferred onto the paper 

• The toner passes through a fusing process to ensure the toner sticks to the paper 

• For colour, the process is repeated 3 times – cyan toner, magenta toner, and yellow toner 

• CCD is more expensive and produces higher quality images 

• CMOS uses less energy, so helps save power on mobile devices 

Secondary Storage Devices: 

Hard Disk Drive

• uses a metal disk (platter) which is coated in a think film of magnetic material

• film is made up of concentric tracks, which are each split up into sectors

• the platter spins at high speed and a read/ write head is moved over the platter, which can detect and change the magnetic charges in that sector

Solid State Disk

• has no moving part

• made up of NAND flash memory and a controller

• NAND flash memory is non-volatile and is based on floating gate transistors

• storage is split into blocks, and each block is split into pages

• pages cannot be overwritten - must be erased first - whole block must be erased

• controller is used to manage this

• have lower latency and faster access speeds than HDDs due to having no moving parts

• have a lower number of read/ write cycles before the flash memory degrades

NAND Flash Memory:

• when the control gate is turned on, electrons flow from the source to the drain and some electrons are attracted to the floating gate

• when the control gate is turned off, the electron flow stops, and the electrons are trapped in the floating gate

• the presence or not of electrons correlates to a 1 or 0

Optical Disk

• includes CD (Compact Disk) and DVD (Digital Versatile Disk )

• data is read using a laser beam (optical = light)

• data is stored on a spiral track and this track uses pits and lands

• the laser is shone at the track

• the laser’s light reflects back to the sensor while the disk spins at a constant linear velocity

• where a pit or land continues, a certain amount if light is reflected back to the sensor and this represents a 0

• if the state changes, the light is scattered and this represents a 1

Comparing Capacity and Speed