Input & Output Devices
Last updated
Last updated
In order to make use of data, computers must be able to use various devices which allow the computer to have data input and output.
Barcodes are visual codes computers can read, using dark and light patterns to represent data.
Airline baggage tracking
Product labelling
Parcel delivery and shipment
Ticketing and identification
There are two main types of barcodes: 1D and 2D. 2D barcodes can 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.
Barcode Readers are input devices which typically work on the principal of reflected light. Light from laser is directed at a pattern and the sensor detects the intensity of light that bounces back. A black bar will absorb more light and be less reflective giving a binary reading of 0 and a white bar will be more reflective with a binary reading of 1. The pattern of 0s and 1s creates a unique identity.
European Article Number (EAN) - Used in retail and warehousing.
Code 128 - Used in shipment and transport tracking.
Code 128 can represent letters and numbers whilst EAN can only represent numeric digits.
When a 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.
In cameras which are able to sense colour, there are multiple cells for each pixel, each of which has a filter that only allows in certain wavelengths of light. This allows 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.
A Bayer filter has the same number of green filters as red and blue combined and allows a camera to produce a closer approximation of what the human eye sees (since human eyes are more sensitive to green light).
A laser printer is an output device that produces images on paper from digital signals. Laser printers, which print whole pages at a time, consist of a laser light source, a mirror, a drum, a toner roller and fusers.
When a document is printed, the drum is positively charged all over before the laser is directed at its surface by the mirror. Areas on which the laser is incident are discharged, leaving behind an impression of the page in electrical charge on the drum.
The toner roller dispenses negatively charged toner (a type of plastic powder) onto the drum. As opposite charges attract, toner is attracted to the positively charged portions of the drum. The toner is then applied to the paper by the drum before the paper is heated by fusers, fixing the toner to the paper.
Colour printers apply the same process with four different colours of toner: cyan, yellow, magenta and black (CYMK) to achieve full colour prints.
1. Data Preparation:
(1) Data is sent to the printer driver.
(2) Driver translates data into a format the printer understands.
(3) Driver checks printer status (toner levels, etc.).
2. Drum Preparation:
(5) A rotating drum is given a negative electrical charge.
3. Image Creation:
(4) Data is sent to the printer and stored in a buffer.
(6) A laser beam scans the drum, removing negative charge where it hits (creating the image).
4. Toner Transfer:
(7) The drum is coated with negatively charged toner particles.
(8) A positively charged sheet of paper is fed over the drum.
(9) The toner sticks only to the positively charged areas of the drum (the image).
5. Fusing and Cleaning:
(10) The electrical charge is removed from the paper to prevent sticking.
(11) The paper passes through a fuser, which uses heat and pressure to permanently bond the toner to the paper.
6. Drum Reset:
(12) A discharge lamp removes the remaining charge from the drum, preparing it for the next print job.
RFID is a method of transferring information wirelessly, between a tag and a reader. RFID is used in contactless credit and debit cards as well as in some hotel room cards.
Inside an RFID tag is a chip which contains a small amount of memory. The chip is attached to a coil of wire which acts as an antenna.
RFID tags, read wirelessly, are used in security, supply chain tracking and payments.
Most RFID tags are passive, meaning that they induce enough power wirelessly from the reader to operate the chip. However, active tags (which contain a small power supply like a battery) also exist.
Active tags can be used much further away from readers than passive tags which must be held within a few centimetres of their reader.
Barcodes can have and prevention methods such as and built in, allowing computers to tell whether a barcode has been read correctly. If a barcode fails to scan correctly, perhaps because the barcode is dirty, the reader will continue to scan until the barcode is read successfully. Barcode readers can scan barcodes 1000s of times a second, so the time delay caused by rescanning is hardly perceptible to humans.
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 , the pixels are stored in the camera's memory.
