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This lesson covers output devices — what they are, how they work, and how to choose the right output device for a given scenario. This is part of OCR J277 Section 1.1.1.
An output device is any hardware component that presents processed data from a computer to the user or to another system. Output devices convert digital data from the computer into a form that humans can understand (such as images on a screen, sound from speakers, or text on paper).
| Feature | Detail |
|---|---|
| How it works | Displays images by lighting up individual pixels in combinations of red, green, and blue (RGB) |
| Types | LCD, LED, OLED, IPS |
| Use | Displaying the operating system, applications, video, and images |
| Key specifications | Resolution (e.g. 1920x1080), refresh rate (e.g. 60 Hz), screen size |
Resolution refers to the number of pixels on the screen. A higher resolution means a sharper, more detailed image:
| Resolution | Name | Pixels |
|---|---|---|
| 1920 x 1080 | Full HD (1080p) | ~2.07 million |
| 2560 x 1440 | QHD (1440p) | ~3.69 million |
| 3840 x 2160 | 4K UHD | ~8.29 million |
There are two main types of printer:
Inkjet Printer:
| Feature | Detail |
|---|---|
| How it works | Sprays tiny droplets of liquid ink onto paper |
| Strengths | High-quality colour printing, good for photos |
| Weaknesses | Slower, ink cartridges can be expensive, ink can smudge |
Laser Printer:
| Feature | Detail |
|---|---|
| How it works | Uses a laser to create a pattern on a drum, which attracts toner (powdered ink) and transfers it to paper using heat |
| Strengths | Very fast, low cost per page, excellent text quality |
| Weaknesses | More expensive to buy, colour laser printers are costly |
| Comparison | Inkjet | Laser |
|---|---|---|
| Speed | Slower | Faster |
| Cost per page | Higher | Lower |
| Photo quality | Excellent | Good |
| Text quality | Good | Excellent |
| Initial cost | Lower | Higher |
| Feature | Detail |
|---|---|
| How it works | A DAC (digital-to-analogue converter) converts digital audio data into electrical signals, which drive a speaker cone or headphone driver to produce sound waves |
| Use | Music, video audio, voice calls, alerts, accessibility |
| Feature | Detail |
|---|---|
| How it works | Projects an image from the computer onto a large screen or wall using a bright light source and lens system |
| Use | Presentations, classrooms, cinema |
| Types | DLP (Digital Light Processing), LCD, LED |
In embedded systems, the output is often a physical action rather than something displayed on a screen. Actuators are output devices that produce movement or control:
| Actuator | What It Does | Example Use |
|---|---|---|
| Motor | Produces rotational movement | Washing machine drum, robot arm |
| Buzzer | Produces sound | Alarm system, timer |
| Heater | Produces heat | Central heating system |
| LED | Produces light | Indicator lights, traffic lights |
| Solenoid / valve | Controls flow of liquid or gas | Irrigation system, fuel injection |
OCR Exam Tip: Actuators are commonly tested in questions about embedded systems. If a question describes an automated system (e.g. a greenhouse), identify the sensors (input) and actuators (output).
Output devices receive data from the CPU through the system bus:
A device driver translates the operating system's instructions into commands the specific output device can understand.
| Factor | Question to Ask |
|---|---|
| Output type | Is the output visual, audio, physical, or printed? |
| Audience | Is it for one person or a group? (monitor vs projector) |
| Quality | How important is output quality? (resolution, sound fidelity) |
| Permanence | Does the output need to be permanent? (screen vs printed copy) |
| Environment | Where will the output device be used? |
| Cost | What is the budget? |
Question: A school wants to display a presentation to a class of 30 students. Suggest an appropriate output device and explain why.
Answer: A projector would be appropriate because it can display the presentation on a large screen visible to all 30 students simultaneously. A standard monitor would be too small for everyone in the classroom to see clearly.
OCR Exam Tip: In scenario-based questions, always name the output device, briefly explain how it works, and justify why it is suitable for the described situation.
Embedded-system scenario questions almost always require you to pair inputs (sensors) with outputs (actuators). A worked example helps lock the pattern into memory.
Scenario: A hobbyist wants to build an automated greenhouse that keeps the air temperature between 18 and 26 degrees Celsius, waters plants when soil is dry, and alerts the owner if something goes wrong. They have a microcontroller, a few sensors, an LCD panel and a small set of actuators. Which output devices should they choose and why?
Step 1 — map each requirement to an output.
| Requirement | Suggested output | How it works |
|---|---|---|
| Cool the greenhouse when too hot | Electric fan (motor actuator) | Motor spins blades that pull cooler outside air through a vent. The microcontroller switches the motor on via a relay when the temperature sensor reads above 26 degrees C. |
| Warm the greenhouse when too cold | Heater (heating element) | A resistive heating element driven by a relay. Switched on when the temperature sensor reads below 18 degrees C. |
| Water plants when soil dry | Solenoid valve + water pump | A solenoid valve opens when the soil moisture sensor reports dryness; a small pump drives water through drip lines. |
| Show current status | LCD panel | A small LCD module receives data from the microcontroller and shows temperature, humidity and last watering time for the owner. |
| Alert owner to problems | Buzzer + LED | A buzzer sounds and a red LED flashes when a sensor reports a value outside a safe range. |
Step 2 — justify the choices in exam language.
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