Computer Science (0478) | Input and output devices

IGCSE Computer Science (0478): Hardware - Input and Output Devices (Section 3.2)

Hello future Computer Scientists! This chapter is all about how computers interact with the outside world. Think of your computer system as a brain: it needs senses to take in information (Input) and muscles to perform actions (Output). Understanding these devices is crucial because they are the eyes, ears, and hands of every computer system you use!

Don't worry if the list of devices seems long; we will break down each one and focus on how they work and when they are used.

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1. Input Devices: Giving Data to the System (3.2.1)

An Input Device is any piece of hardware that allows data to be entered into a computer system for processing. They are required because raw, real-world data (like sound, movement, or images) needs to be converted into a digital, binary format (1s and 0s) that the Central Processing Unit (CPU) can understand and process.

Memory Trick: Input means In!

Key Input Devices and Their Uses

• Keyboard: Used for inputting text and commands. It converts key presses into binary codes (like ASCII or Unicode).
• Optical Mouse: Tracks movement (2D data) using a light source (usually LED or laser) and a sensor on the underside.
• Microphone: Captures sound waves and converts them into electrical signals, which are then converted into digital sound files.
• Digital Camera: Captures visual images (light) and records them as pixels. These pixels are converted into binary data to form an image file.
• Scanners (2D and 3D):
  • 2D Scanners capture flat images (like documents or photos) and convert them into digital files.
  • 3D Scanners capture the shape and form of physical objects, creating a three-dimensional model used in design or manufacturing.
• Barcode Scanner/QR Code Scanner: Used to read optical patterns (lines or squares) that represent binary encoded data (typically numbers or URLs), making data entry fast and accurate, such as at a supermarket checkout or for accessing a website link.

Deep Dive: Touch Screens

A Touch Screen is special because it can act as both an input and an output device, but its primary function when being touched is inputting positional data.

You need to know the three main types and how they work:

1. Resistive Touch Screen:
   • How it works: Uses two flexible layers separated by a tiny gap. When you press (resist), the layers touch, completing a circuit and registering the pressure point.
   • Suitability: Can be used with fingers, stylus, or gloved hands. Often found in older devices or environments like factories where gloves are necessary.
2. Capacitive Touch Screen:
   • How it works: Uses electrical fields. The screen layers store an electrical charge. When a finger (which is conductive) touches the screen, it draws a small amount of charge to that point, which is then registered as the touch location.
   • Suitability: Very responsive, supports multi-touch gestures (like pinching/zooming). Used in modern smartphones and tablets. Cannot be operated with non-conductive materials (like a regular plastic pen).
3. Infra-red Touch Screen:
   • How it works: Uses a grid of infra-red LEDs and sensors around the screen edge. When the screen is touched, the infrared beams are broken at that specific point, registering the position.
   • Suitability: Can detect any input (finger, pen, glove). Often used for large displays, like public kiosks or interactive whiteboards.

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2. Output Devices: Displaying the Results (3.2.2)

An Output Device is any piece of hardware that allows the processed data (results) to be shown or transmitted out of the computer system, converting binary back into a format humans can understand (like pictures, text, or sound).

Memory Trick: Output means Out!

Key Output Devices and Their Uses

• Printers (Inkjet and Laser):
  • Inkjet Printer: Sprays tiny droplets of ink onto the paper. Good for high-quality colour photos and small print jobs.
  • Laser Printer: Uses toner (powdered ink) and static electricity, fixing the toner to the paper using heat (a fuser). Faster and better for high-volume, black-and-white text printing.
• Screens (LCD and LED): Both display images using pixels.
  • LCD (Liquid Crystal Display) Screen: Uses liquid crystals and a backlight (usually fluorescent or LED).
  • LED (Light Emitting Diode) Screen: Similar to LCD, but uses LEDs for the backlight. LEDs are brighter, more energy-efficient, and produce better contrast.
• Projectors (LCD and DLP): Output large display images onto a surface.
  • LCD Projector: Uses three separate LCD panels (for red, green, and blue light) which recombine the image before projecting.
  • DLP (Digital Light Processing) Projector: Uses millions of tiny mirrors (micro-mirrors) on a chip (DMD) to reflect light and create the image. Offers smooth, high-quality images.
• Speaker: Converts digital audio signals back into analogue electrical signals, which are then used to vibrate a cone and produce sound waves.
• 3D Printer: Builds physical, three-dimensional objects layer by layer from a digital model (CAD file). This is a purely physical output device.
• Actuator: This is an important output component, especially in automated systems (like robotics). It takes electrical signals from the computer and converts them into physical motion, such as turning a valve, opening a door, or moving a robotic arm.

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3. Automated Systems: Sensors and Actuators (3.2.3)

When computers interact with the real world, especially in automated systems (like self-driving cars or climate control in a building), they rely on sensors for input and actuators for output.

What is a Sensor? (Input)

A Sensor is an input device designed to detect and measure physical input from the environment and convert this into an electrical signal that the computer can process. Sensors are the eyes, ears, and thermometers of automated systems.

What is an Actuator? (Output)

An Actuator is an output device that controls a mechanism or system by converting energy (usually electrical) into physical motion or action. It executes the decision made by the microprocessor based on the sensor data.

Analogy: If a human touches a hot stove (Sensor Input: detects temperature), the brain decides the action, and the muscle (Actuator Output: pulls the hand away).

Sensor Types, Data Captured, and Suitability (The Important Table)

You must be able to Identify the type of data captured by each sensor and understand when each sensor would be used (its suitability).

Don't worry about knowing exactly how they work internally, just what they measure and where you would find them!

Sensor Type	Data Captured	Suitability / Example Use
Acoustic Sensor	Sound levels/volume	Security alarms (detecting breaking glass), noise pollution monitoring.
Accelerometer	Movement, G-force, vibration	Airbags in cars (detecting sudden deceleration), measuring shaking in buildings, fitness trackers.
Flow Sensor	Speed/rate of fluid (liquid or gas) movement	Monitoring water usage in pipes, ensuring correct fuel delivery to an engine.
Gas Sensor	Presence and concentration of specific gases (e.g., methane, CO2)	Detecting leaks in chemical plants, monitoring air quality in mines.
Humidity Sensor	Moisture content in the air (water vapour)	Controlling climate in greenhouses, monitoring storage rooms for sensitive documents.
Infra-red Sensor	Heat radiation, presence of objects (often passive detection)	Night vision cameras, intruder detection (PIR sensors), detecting temperature in a non-contact way.
Level Sensor	Height or depth of a substance (liquid or solid)	Measuring fuel in a tank, monitoring water levels in a reservoir.
Light Sensor	Light intensity (brightness)	Automatic street lights (turning on when it gets dark), adjusting screen brightness on a phone.
Magnetic Field Sensor	Presence or strength of a magnetic field	Detecting when a door is closed (used in security systems), compass navigation in phones.
Moisture Sensor	Water content/wetness in soil or other substances	Automated watering systems in agriculture, controlling soil humidity in large farms.
pH Sensor	Acidity or alkalinity (pH level) of a liquid	Chemical analysis, monitoring acidity levels in large fish tanks or water treatment plants.
Pressure Sensor	Force exerted over an area (weight or internal pressure)	Monitoring tire pressure in cars, measuring weight on a factory conveyor belt.
Proximity Sensor	Detecting the presence or absence of an object nearby (without touching it)	Automated doors (opening when a person is near), detecting objects in robot pathways.
Temperature Sensor	Heat or cold	Controlling heating systems, monitoring fridge/freezer temperatures, preventing machine overheating.