3.7.4.1 Input and Output Devices. Flashcards
What is a barcode?
Printed diagrams that consist of light and dark portions.
Name the two types of barcodes.
1D and 2D.
Give an advantage of a 2D Barcode.
Can contain more information in the same amount of space as a 1D barcode.
Give a disadvantage of a 2D barcode.
They require more processing in order for the information to be extracted.
Name the parts of a barcode reader.
Laser light source.
Lens.
Photodiodes.
Mirror.
What role does the mirror play in a barcode.
Reflects light from the laser onto a printed barcode. The light reflected passes through the lens and is incident on the photodiode.
What role does the photodiode play in a barcode.
Turns the light into an electrical charge.
What happens once the light is converted into an electrical charge (barcode).
The electrical charge can be measured and processed to form a digital signal representing the contents of a barcode.
What is the purpose of the light and dark portions on a barcode?
Light portions reflect most of the light whereas dark sections absorb incident light.
What do the light and dark portions in a barcode correspond to?
Binary: 1,0.
What error detection and prevention methods does a barcode have?
Parity bits and check digits built in, allowing computers to tell whether a barcode has been read correctly.
What happens if a barcode fails to scan correctly?
Possibly due to dirt on the barcode, the reader will continue to scan until the barcode is read successfully.
How many time can a barcode read a barcode in a second.
1000s of times per second.
What do digital cameras consist of?
A lens that focuses light on a sensor.
What regulates the path of light (dc).
The path of light
between the lens and the sensor is regulated by a shutter.
What are the two sensors commonly used in digital cameras?
CMOS (Complementary metal oxide semiconductor).
CDD (Charge coupled device).
What do both sensors do (DC).
Convert incident light into electrical charge.
What represents a pixel in the image? (DC).
Charge builds up in cells, each of which represents a pixel in the image.
What happens once the photograph has been taken?
The charge in each cell is measured and converted to a digital value which is then processed by the camera and stored as a digital image.
How many cells are for each pixel in a colour camera.
Multiple, each of which has a filter that only allows in certain wavelengths of light.
What do the certain wavelength of lights allow for?
The camera to build up a separate image for the intensity of each colour of light which can then be combined to form a full colour photograph.
What is a Bayer filter?
A special colour filter used in digital cameras that
has the same number of green filters as red and blue combined.
What is an advantage of a Bayer filter?
Produces an image that is a closer approximation of what the human eye, which is most sensitive to green light, sees
What is a laser printer?
An output device that produces images on paper from digital signals.
What do laser printers consist of?
Laser printers, which print whole pages at a time, consist of:
Laser light source. A mirror. A drum. A toner roller. A fuser.
What happens when a document is printed?
The drum is positively charged all over before the laser is directed at its surface by the mirror.
What happens to the areas on which the laser is incident?
They are discharged, leaving behind an impression of the page in electrical charge on the drum.
What charged toner does the toner roller dispense onto the drum?
The toner roller dispenses negatively charged toner (a type of plastic powder) onto the drum.
What is the toner attracted to?
As opposite charges attract, toner is attracted to the positively charged portions of the drum.
What is then done with the toner?
The toner is then applied to the paper by the drum before the paper is heated by
fusers, fixing the toner to the paper.
What differs from this process when working with a coloured printer?
Colour printers apply the same process except with four different colours of toner: cyan, yellow,
magenta and black (CYMK) to achieve full colour prints
Define an RFID.
Radio frequency identification.
Method of transferring information wirelessly between a tag and a reader.
Give examples of when RFID is used.
Contactless credit and debit cards.
In some hotel room cards.
Outline the role of the chip in the RFID tag.
To contain a small amount of memory. The chip is attached to a coil of
wire which acts as an antenna.
What is meant when we say an RFID tag is passive?
They induce enough power wirelessly from the reader to operate the chip.
What is meant when we say an RFID tag is active?
Contain a small power supply like a batter.
Can be used much farther away from readers than passive, which must be held within a few centimetres of their reader.
What is stage one of scanning a barcode?
When an RFID tag is scanned, the reader emits radio waves which are picked up by the
tag’s antenna.
What is stage two of scanning a barcode?
The power induced in the tag’s antenna from these waves is enough to power the chip
What is stage three of scanning a barcode?
The chip then uses its antenna to emit its own radio wave
What is stage four of scanning a barcode?
The radio wave contains the information held on the chip. This wave is picked up by the reader which decodes the information and returns the information to a computer.
