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Topic 5/Topic 6 (Barcode readers (Light from a laser is directed at a…
Topic 5/Topic 6
Barcode readers
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Light from a laser is directed at a pattern and a
sensor detects the intensity of light that bounces
back
A black line will absorb more light and be less reflective, giving a 0 binary value
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Types
(UPC-A) used in warehouses, can only represent digits
Code 128 (use for shipment, can represent letters and digits)
RFID
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The powered receiver emits radio frequency energy
The transponder antenna in the bank card, mobile phone or tag becomes energised by radio waves
The transponder can then send data to the receiver
Passive and active tags
Passive transponders, used in bank cards for example, have no power source themselves and rely on the radio waves from the receiver for their energy
Active tags use a larger, battery powered beacon which can broadcast its own signal to receivers up to 300m away
Digital cameras
When a digital camera captures an image it breaks
up what it sees through its lens into a grid of pixels
The shutter opens to let light onto a Charge-Coupled Device
(CCD) or Complementary Metal Oxide Semiconductor
(CMOS) sensor at the back of the lens. The intensity of light is measured by millions of tiny sensors (one per pixel) arranged in a grid on the sensor. Light levels for each pixel are represented as binary values. This information is now stored as an image in the camera's memory
Sensing colours
The intensity of each of these colours falling on the sensors is measured and stored to aggregate an RGB value
Red, Green or Blue filters are used with different sensors in the camera to separate out these wavelengths
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SSD
A Solid State Disk comprises millions of NAND flash memory cells. Cells are also managed by a controller that organises pages and blocks of memory
The advantages of an SSD over a traditional Hard Disk are as follows: Faster access speed as there is no moving read/write head. Lower power consumption. Extended battery life in portable devices. Devices stay cooler Less susceptible to damage. Silent in operation. Lighter in weight
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Laser printers
A print drum is given a negative static charge
A laser shines a reverse image of the page at the drum
Laser light reverses the charge on the drum
Toner is charged negatively and sticks to positively charged image
Toner is transferred from drum to the paper and fused using a heat roller
Tracks, sectors and platters
Concentric tracks are created on a magnetic disk
Disk spins at high speed: 3,600 – 7,200rpm
Spinning platters are each read by drive heads
Data is read or written as sector moves under the head
Development of HDDs
Fitting more data in the same physical space has required technological changes
More densely packed platters
Smaller magnetic parts and read/write heads
Disk Latency
Latency is the time taken to read/write disk data
This includes: Seek delay - the time the head takes to move across the disk. Rotational delay - the time the disk takes to move to the correct sector underneath the read/write head. Transfer time to move the actual data
Software mailing
Often best suited to optical disks. Cheap to manufacture and distribute. Robust during carriage. Lightweight
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