CHAPTER 02 – OUTPUT DEVICES
Contents
CRT (Cathode Ray Tube) Monitors These are becoming increasingly rare as TFT monitors are now the most common type of screen. They use an electron gun to fire against a phosphor screen, which creates a picture that is made up of tiny dots. Each dot is coloured red, green or blue – the intensity of each coloured dot makes up the vast range of colours interpreted by the eye.
TFT (Thin Film Transistor) Monitors These are the most common output device on computers. They were a leading reason for the rapid development of laptop computers. Screen is made up of thousands of tiny pixels which are made up of transistors controlled by a microprocessor. Each pixel has three transistors, coloured red, green or blue; the intensity of each governs the effective colour of the pixel seen by the eye Uses: Uses:
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Disadvantages: Disadvantages:
Laser Printers They produce very high quality hard copy output. The print rate per page is very quick if a large number of pages are being printed. They rely on large buffer memories, where the data for the whole document is stored before the pages can be printed out
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Inkjet Printers These are used to produce good quality hard copies. Although the quality is not quite as good as that from laser printers, it is far better than that from a dot matrix. Unlike laser printers, inkjet printers do not have large buffers, so printing is done a bit at a time. This is why printing is sometimes paused, since the whole page can’t be stored in the buffer and it has to wait for the computer to send more data. Uses:
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3D Printers These are a fairly recent type of printer that produces solid 3D models using modified inkjet technology. IN this technology, known as tomography thin layers of fine powder (plaster, resin and starch) are bonded together as a 3D model in thin layers (each layer is about 0.25mm thick).
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Dot matrix printers These are a type of impact printer where a printhead (made up of a matrix of pins) presses against an inked ribbon. They tend to be slow, noisy and the output is not of a good quality. They are still useful; however, where multi-part or continuous stationery (e.g. long reams of perforated paper) is being used.
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Plotters (also known as graph plotters) These are devices that produce hard copies, but operate in a different way to printers. They are not limited to normal printer paper size and are capable of producing highly accurate, very large drawings and posters. The most common types are: •
pen plotters (which use coloured pens to draw),
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electrostatic (similar method to laser printers)
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inkjet (same method as inkjet printers)
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Speakers These can be connected directly to a computer or are built into the monitor or casing (as in a laptop computer). Digital data from the computer is converted into analogue form, using a digital to analogue converter (DAC). The signal is then amplified through the speakers.
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Multimedia Projectors These receive signals that can be either analogue or digital, although most modern projectors only work with digital inputs. The signal source is usually from a computer, television or DVD player. The image from the source is magnified and projected onto a large screen. The devices usually work with a remote control, but can also use virtual mouse technology (i.e. wireless mouse or “clicker�). It is then possible to direct the computer presentation without being tied to the computer. Another feature of the virtual mouse is the laser pointer. Most multimedia projectors take input from various types of video format such as NTSC, PAL or SECAM.
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Control Devices These are another type of output device. They are used to control processes in conjunction with inputs from sensors. More detail will also be found in Chapter 7.
Actuators Actuators are transducers and are used to take signals from a computer and convert them into some form of motion, for example operating motors, pumps, switches and valves. As part of the control process, digital signals are sent from the computer to an actuator to operate a device. Usually conversion of the digital signal to analogue is required first (using DAC).
Motors Can be turned on or off by the actuator. Uses:
Buzzers Can be switched on or off by the actuator. Uses:
Lights The actuator is connected to the switch that turns the lights on or off. Uses:
Heaters Actuators are connected to switches which turn the heater on or off. Uses:
Task 1: Complete the table below: Application
Most suitable output device
Alerting the user that an error has occurred by making a beep Printing a poster in colour Listening to the radio online Producing a large plan of a house Producing a hard copy of a spreadsheet Producing a colour picture on paper taken with a digital camera Producing a series of invoices wither several copies that can be sent to different departments Producing a warning when a bar code is read incorrectly For listening to messages from a voicemail system Displaying the results of a quick search on the availability of a holiday
Task 2: List at least 3 situations, with descriptions of where specific output devices could be used either to prevent danger or to rescue people from danger.
Task 3: Consider the following types of organisations: •
Animated film studio
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A bank
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A hospital
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Your school
List and describe four output devices you might find in each organisation. State their advantages and disadvantages.