4.7.4 External hardware devices Flashcards
What are the Input / Output devices we need to learn for this topic?
Barcode Reader, Digital Cameras, Laser Printer, RFID
What is a barcode?
A barcode is a printed diagram that consists of light and dark portions. They contain information which can be read by a computer using a barcode reader.
What types of barcodes are there?
1D - supermarket kind
2D - typical QR code
Why do we still use 1D barcodes if we have 2D barcodes?
2D barcodes contain more information in the same amount of space as 1D barcodes, however, they require more processing in order for the information to be extracted.
How does a barcode reader work?
- Mirror directs light from laser onto printed barcode.
- Light reflected by barcode passes through the lens.
- This light is incident on the photodiode which turns light into electrical charge.
- This electrical charge can be measured and processed to form a digital signal representing the content of a barcode.
How does the light reflect in a barcode?
Light portions of the barcode reflect the most light while dark sections absorb incident light. The pattern of light and dark correspond to binary 1s and 0s.
How do the barcode readers prevent error?
Barcodes can have error detection and prevention methods such as parity bits and check digits built in.
If the barcode fails the scan correctly, the reader will continue to scan until read successfully. Readers can scan barcodes 1000s of times a second, so the time delay is hardly perceptible to humans .
How does a digital camera work?
- The shutter opens to let light onto the sensor at the back of the lens.
- Sensors convert the incident light into electric charge.
- Charge builds up in cells, each cell represents a pixel in the image.
- Once photograph is taken, the charge on each cell is measured and converted to a digital value and processed by camera, stored as a digital image.
How does the process for color cameras differ from digital camera?
Color cameras have multiple cells for each pixel, each has a filter to allow only certain wavelengths of light in. This lets the camera build up a separate image for the intensity of each color of light, which is combined to form a full color photograph.
How does a laser printer work?
- The drum is positively charged all over before the laser is directed at its surface with a mirror.
- Areas on which the laser is incident are discharged, leaving an impression or bitmap image in electric charge on the drum.
- The toner roller dispenses negatively charged toner (plastic powder) onto the drum.
- Opposite charges attract ; the negatively charged toner is attracted to the positively charged portions of the drum.
- A sheet of paper is passed under the drum and the toner is applied on the paper.
- The paper is then heated by the fusers to fix the toner to the paper.
What are the 4 different toner cartridges in a laser printer?
CYMK - Cyan, Yellow, Magenta, Black.
What is RFID?
RFID stands for Radio Frequency Identification.
It is a method of transferring information wirelessly between a tag and a reader.
What is inside an RFID tag?
Inside a RFID tag is a chip which contains small amounts of memory. The chip is attached to a coil of wire acting as an antenna.
What does it mean if RFID tags are passive?
RFID tags that are passive (majority) mean that they do not contain power supply, so they induce enough power wirelessly from the reader to operate the chip.
What does it mean if RFID tags are active?
RFID tags that are active(minority), mean that they do contain a small power supply - battery. These can be used much further away from readers than passive tags.
