Learning Objectives
- Describe the operation and uses of the output devices named in the syllabus.
- Compare inkjet and laser printers for appropriate applications.
- Compare LCD and DLP projectors and LCD and LED screen technologies at syllabus level.
- Explain the role of speakers and three-dimensional printers.
- Explain how an actuator allows a computer to control a physical process.
Key Terms
- Output device
- Hardware that presents processed information or produces an action from a computer system.
- Actuator
- An output device that converts a control signal into physical movement or another physical action.
- Inkjet printer
- A printer that forms an image by spraying tiny droplets of ink onto paper.
- Laser printer
- A printer that uses a laser, charged drum, toner and heat to produce a printed page.
- LCD
- Liquid crystal display technology in which liquid crystals control the passage of light.
- LED screen
- A display that uses light-emitting diodes, commonly as a backlight for an LCD panel at this level.
- DLP projector
- A digital light processing projector that uses many tiny mirrors to direct light.
- LCD projector
- A projector that passes light through liquid crystal panels to form an image.
- Speaker
- An output device that converts an electrical audio signal into sound waves.
- 3D printer
- An output device that creates a physical object by adding material in successive layers.
- Toner
- Fine powder used by a laser printer to form the printed image.
- Hard copy
- Output produced on a physical medium such as paper.
Inkjet And Laser Printers
An inkjet printer moves a print head across paper and sprays microscopic droplets of liquid ink through nozzles. Different coloured inks are combined to produce colour output. Inkjet printers are often inexpensive to purchase, compact and capable of high-quality photographic colour output, but ink costs can be high and printing large quantities may be slow.
A laser printer uses an electrostatic process. A laser creates a charge pattern on a rotating drum. Toner is attracted to the charged image, transferred to paper and fused by heat and pressure. Laser printers are generally fast for high-volume text, produce sharp output and have a low cost per page at substantial volumes, although initial purchase cost and physical size may be greater.
Selection should be based on workload. A home user printing occasional colour photographs may prefer inkjet. An office producing many text documents may prefer laser. Avoid claiming that one technology is always better in every situation.
Screens And Projectors
An LCD screen uses liquid crystals to control how much backlight passes through each pixel. Colour filters produce red, green and blue components. An LED screen in this syllabus context commonly refers to an LCD panel illuminated by light-emitting diodes rather than older fluorescent backlighting. LED backlighting can allow thin displays, efficient power use and good brightness.
An LCD projector shines a powerful light through liquid crystal panels. The panels control the red, green and blue parts of the image, which are combined and projected through a lens. A DLP projector uses a digital micromirror device containing many tiny mirrors. Each mirror directs light towards or away from the lens to form pixels, with colour produced using colour-separation methods.
A projector is suitable when the same enlarged image must be seen by a group. A direct-view screen is more suitable for individual use, normally gives a clearer image in ordinary lighting and does not need a projection surface.
Speakers And 3D Printers
A speaker receives an electrical audio signal. A changing current in a coil interacts with a magnet, moving a cone back and forth. The movement produces pressure waves that the user hears as sound. Digital audio must be converted into an analogue signal before driving the speaker.
A 3D printer creates a physical object from a digital model. Software divides the model into thin layers. The printer deposits, cures or fuses material for one layer and then adds the next. The process continues until the object is complete. Applications include prototypes, customised components, medical models and low-volume manufacturing.
Three-dimensional printing is additive because material is built up rather than removed from a solid block. It can create complex shapes and customised items, but printing may be slow, materials can be limited and a printed object may require finishing.
Actuators In Control Systems
An actuator converts a computer control signal into physical action. Examples include an electric motor, valve, relay, solenoid, pump or heater controller. The processor normally cannot supply enough power to operate the device directly, so an interface or driver circuit is used.
Actuators are central to automated systems. A sensor supplies input, the processor compares the input with programmed conditions, and an actuator changes the physical system. For example, a temperature sensor may cause a controller to switch a fan motor on.
The actuator is output hardware even when its result is not information shown to a person. Opening a valve, turning a motor or sounding an alarm are all outputs because the computer causes an external action.
Inkjet And Laser Printers Compared
| Feature | Inkjet | Laser |
|---|---|---|
| Method | Sprays liquid ink droplets through nozzles. | Uses laser, charged drum, toner and heat. |
| Purchase cost | Often lower. | Often higher. |
| High-volume speed | Usually less suitable for very large text runs. | Usually faster and more suitable. |
| Colour photographs | Often strong for occasional high-quality photo output. | Colour models exist but may cost more. |
| Running pattern | Cartridges can be costly and ink may dry if rarely used. | Toner often gives lower cost per page at high volume. |
Output Device Selection
| Need | Suitable Device | Justification |
|---|---|---|
| Show a presentation to a large class | LCD or DLP projector | Produces an enlarged image visible to a group. |
| Print thousands of text pages | Laser printer | Fast output and economical at high volume. |
| Produce occasional colour photographs | Inkjet printer | Good colour and photo quality at modest purchase cost. |
| Create a physical prototype | 3D printer | Builds an object from a digital three-dimensional model. |
| Play recorded speech | Speaker | Converts an audio signal into sound waves. |
| Open an automatic valve | Actuator | Converts a control signal into physical movement. |
Worked Examples
Selecting A Printer
Question: A school office prints 6000 mostly black-and-white pages each month. Recommend a printer type and justify the choice.
- The workload is high volume.
- Most pages are text and do not require photographic inkjet output.
- A laser printer is generally fast for page printing.
- Toner cost per page is normally economical at sustained volume.
Answer: A laser printer is suitable because it produces sharp text quickly and is cost-effective for a large monthly print volume.
Explaining A Heating Controller
Question: A room controller switches an electric heater on when temperature is below a set value. Explain the role of the actuator.
- The temperature sensor supplies an input value.
- The processor compares it with the set value.
- The processor sends an output control signal.
- A relay or switching actuator controls the larger current supplied to the heater.
Answer: The actuator converts the low-power computer signal into the physical switching action that turns the heater on or off.
Examination Guidance
- Describe both the operating method and a suitable application when asked about an output device.
- Compare printers using purchase cost, speed, volume, quality and running cost rather than one vague claim.
- Remember that LED screens at this syllabus level commonly use LEDs to backlight an LCD panel.
- For 3D printing, mention a digital model, layers and the creation of a physical object.
- Identify actuators as output devices and connect them to sensor-based control.
Common Mistakes
- Saying a laser printer burns the final text directly onto paper.
- Saying an inkjet printer uses toner powder.
- Confusing a projector, which gives output, with a camera, which captures input.
- Describing a 3D printer as a 3D scanner.
- Calling a sensor an actuator because both appear in an automatic system.
Knowledge Check
1. How does an inkjet printer form an image?
2. What material forms the image in a laser printer?
3. How does a DLP projector form pixels?
4. How does a speaker produce sound?
5. What is the purpose of an actuator?
