5.5 - Input/Output Devices Flashcards
What are the uses of barcodes?
- airline baggage tracking
- product labelling
- parcel delivery and shipment
- ticketing and identification
How does a barcode reader work?
By the principle of reflected light:
- light from a spinning laser is directed at a pattern and a sensor detects the intensity of light that bounces back
- the reflected light is converted into a digital signal (black bar absorbs more light and are less reflective, white bar is more reflective. Represents different digital signals)
What do the different groups of numbers on the barcode represent?
Left = manufacturer number
Right = product number
Last digit = check digit
What are QR codes and what can they contain?
2D barcodes that contain more information in the same amount of space as a 1D barcode but require more processing in order for the information to be extracted
Contain links to websites or information
What are common uses of QR codes?
- restaurant coupons
- mobile concert tickets
- estate agency boards
- business cards
- tourist information
- advertising posters
How do digital cameras work?
Consists of a lens that focuses light onto a sensor
Path of light between the lens and the sensor is regulated by a shutter
What is a barcode?
Printed diagram that consist of light and dark portion
They contain information which can be read by a computer using barcode reader
What type of error detection to barcodes have?
Parity bits & check digits
What are CMOS and CCD?
Two sensors commonly used in digital cameras which convert incident light onto electrical charge
Charge builds up in cells each of which represents a pixel in the image
Once the picture is taken the charge on each cell is measured and converts to a digital value each is processed by the camera and stored as a image
How do colour cameras produce an image differently?
There are multiple cells for each pixel each of which has a filter that only allows in certain wavelengths of light
This lets the camera build up a separate image for the intensity of each colour of light which can then be combined to form a full colour photograph
How does a laser printer work?
- Data to be printed is first sent to the printer driver
- Printer driver puts data into a format that the printer can process
- Printer driver checks the status of the printer
- Data sent to the printer and then stored in printer buffer
- Printing process starts by giving printer drum a negative charge
- As printer drum rotates a laser beam scans across removing the negative charge in certain areas; this leaves positively charge areas which match the text or image to be printed
- Printer drum is coated with negatively charged toner; it only sticks to the positively charged parts of the drum
- Positively charged sheet of paper is then rolled over the drum
- Toner on the drum now sticks to the paper producing exact copy of the text and images
- To prevent paper sticking to the drum the electric charge is removed once the page has been printed
- Paper goes through a fuse which bonds the ink making a permanent copy
- A discharge lamp removed the electric charge from the serum making it ready for the next page
What is RFID (radio frequency identification)?
Method of transferring information wirelessly between a tag and a reader
What is a passive RFID tags?
They induce enough power wirelessly from radio waves sent by the reader to operate the chip
No power source themselves
What is the hardware like inside an RFID tag?
Contain a chip which contains a small amount of memory. The chip is attached to a coil of wire which acts as an antenna
Why can active tags be used much further away from readers than passive tags?
As they contain a small power supply like a battery
What are some uses of RFID tags?
- security control points
- identification of people, animals, goods or valuables
- shipping and supply tracking for goods
- banking and fast payment systems
- potential replacement for barcode systems
How is an RFID tag read?
- When scanned the reader emits radio waves which are picked up by the tag’s antenna
- Power induced in the tag’s antenna from these waves is enough power to chip
- The chip then uses its antenna to emit its own radio wave which contains the information held on the chip
- This wave is picked up by the reader which decides the information and retorts the information to a computer
