Input output devices Flashcards
what do barcodes do
Barcode readers are used to quickly and accurately scan barcodes
when are 2d barcodes used
- ticketless entry to concerts
- ## boarding trains
advantages of laser scanners
- available in a variety of forms
- reliable and economical for low volume applications
examples of laser scanners
- CCD readers
- Camera based readers - used for age verification or event ticketing
how do digital cameras work
- shutter opens to let light on CCD
- Each sensor produces an electrical current/signal
- The signal represents a pixel;
An (ADC) converts measurement of light intensity into binary/digital data;
-filter is applied to generate separate data values for red, green and blue
colour components; - The pixels are recorded as a group / array;
what does a digital camera use
a CCD or CMOS
advantages of CCD sensor
- produces higher quality images
- used in higher end cameras
- more reliable since the technology has been around longer
disadvantages of a CCD compared to a CMOS
- cost of power consumption, uses up to 100 times that of CMOS sensor
what are RGB filters used for
to separate out wavelengths
how do RFIDs work
- RFID tag contains circuitry and antenna
- RFID reader transmits electromagnetic field
- signal activates current in RFID tag
- RFID reader converts radiowaves back into binary
how does a laser printer work
- printer generates bitmap from the data
- printer drum coated in charge
- laser beam shone on drum
- laser removes electric charge on drum
- toner is given positive charge
- charged drum picks up toner(one for each colour)
- toner transferred to paper
- toner is fused while on paper
- discharge lamp removes any remaining electrical charge
how to prevent sticking in laser printing
the electric charge on the drum is removed
how does a barcode work (light source)
- light source directed at barcode
- prism moves light beam across barcode
- light is reflected back
- black reflects less light, white reflects more
- light sensor measures the intensity of light reflected back
- and converts it into binary
digital camera barcodes process
- CMOS sensor measures light intensity at a point
- sensor outputs voltage, dependent on light intensity
- voltage turned into binary via ADC
- image processing software analyses image
- and identifies black and white bars in barcode
How do optical discs read
- laser shone on disk
- light is focused on spot on track
- light is reflected back from disk
- amount of light reflected is measured
- disc spins at constant linear velocity
hows data represented using a disc
- data is stored on one track
- continuation of pit reflects light whereas transition between land and pit scatters light
- transition between land and pit indicates a 1 and continuation of land/pit represents 0
advantages and disadvantages of secondary storage
advantages - provides non-volatile memory that retains information even when the computer is turned off. This enables long-term storage of programs
disadvantages - secondary storage is not directly accessible to the processor and has slower access speeds
problems with primary storage
its volatile, if you turn the computer off, data gets lost