# Output Devices & Actuators

- **Track:** Cambridge IGCSE™ Computer Science (0478 / 0984) (CAMBRIDGE IGCSE 0478)
- **Module:** Section 3: Hardware & Architecture
- **Estimated Duration:** 15 minutes
- **Access:** Open Theory (All-Access for Interactive IDE & Autotests)

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## Theory & Conceptual Background

An output device makes processed information available to a person or changes a physical condition.

## Displays and projectors

An LCD controls light passing through liquid crystals to form an image. In an LED-backlit LCD, LEDs supply the backlight. A screen is useful for changing information viewed directly by its user.

An LCD projector shines light through liquid-crystal panels and lenses to project an enlarged image. A DLP projector uses many tiny tilting mirrors to direct light and form the projected image. A projector suits a class presentation; lighting conditions, distance and a suitable surface affect visibility.

## Sound and movement

A speaker uses an electrical signal to move a cone and vibrate the air, producing sound. Stored digital audio is converted to an analogue signal by a DAC before suitable amplification/output.

An actuator changes a physical condition in response to a control signal. A motor can rotate a fan, a valve can release water, and a heater can raise temperature. A temperature sensor is not an actuator: it measures rather than heats.

## Worked decision

A station needs visible departure information and announcements. A display shows changing text; speakers provide audible announcements. Neither alone meets both needs. A motor operating a barrier is another output, even though it does not show information.

Printer mechanisms are studied separately so each can be compared and practised.

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## Interactive Exercises & Autotest Specifications

### Exercise 1: Exam-Style Check: The Role of Actuators (Multiple choice, 25 XP)

**Instructions:**
What is the primary role of an actuator in an automated computer control system?

**Options:**
- **A**: To measure environmental physical variables like temperature or humidity.
- **B**: To convert digital electrical control signals from a computer into physical mechanical movement.
- **C**: To convert analogue sound waves into digital binary samples.
- **D**: To perform arithmetic addition and subtraction inside the CPU.


**Autotest Expectations:**
- **Correct option selected**: `selection_match` -> Expected: `b`

### Exercise 2: Application: Outputs (Fill in blank, 30 XP)

**Instructions:**
Work out each answer before submitting. Which projector uses tilting mirrors: DLP or LCD? Which output produces sound by vibrating air? Does an actuator measure or change a physical condition?


**Starter Code:**
```text
{"prompt":"Application: Outputs","template":"1. Which projector uses tilting mirrors: DLP or LCD? [blank_1]\n2. Which output produces sound by vibrating air? [blank_2]\n3. Does an actuator measure or change a physical condition? [blank_3]","blanks":[{"id":"blank_1"},{"id":"blank_2"},{"id":"blank_3"}],"word_bank":["DLP","LCD","speaker","microphone","change","measure"]}
```


### Exercise 3: Application: Check the reasoning (Fill in blank, 30 XP)

**Instructions:**
Work out each answer before submitting. Output device that moves a barrier: sensor or actuator? Converter for digital audio to a speaker signal: Which projector uses liquid-crystal panels: DLP or LCD?


**Starter Code:**
```text
{"prompt":"Application: Check the reasoning","template":"1. Output device that moves a barrier: sensor or actuator? [blank_1]\n2. Converter for digital audio to a speaker signal: [blank_2]\n3. Which projector uses liquid-crystal panels: DLP or LCD? [blank_3]","blanks":[{"id":"blank_1"},{"id":"blank_2"},{"id":"blank_3"}],"word_bank":["actuator","sensor","DAC","ADC","LCD","DLP"]}
```