Input and output devices

1. Overview

Input and output devices are the bridge between humans and computers. Without input devices, we couldn't communicate instructions or data to the computer. Similarly, without output devices, the computer couldn't communicate results or information back to us. Understanding these devices is crucial for designing effective and user-friendly computer systems.

Key Definitions

• Input Device: Hardware that allows a user or the environment to send data to a computer.
• Output Device: Hardware that receives data from a computer and presents it to the user in a readable form.
• Sensor: A device that detects a physical property (e.g., temperature, light) and converts it into an electrical signal that a computer can process.
• Actuator: A type of output device that converts an electrical signal into physical movement (e.g., a motor turning, a valve opening).
• Resistive Touch Screen: A touchscreen that detects pressure to determine the touch location.
• Capacitive Touch Screen: A touchscreen that detects changes in an electrical field to determine the touch location.
• Analogue Data: Continuous data that varies smoothly over time (e.g., temperature readings from a sensor).
• Digital Data: Discrete data represented as a sequence of bits (0s and 1s).
• ADC (Analogue-to-Digital Converter): A component that converts analogue data from sensors into digital data that a computer can understand.

Core Content

Input Devices

• These devices allow us to get data into the computer.

• They are necessary to enter data, instructions, and commands.

• Examples:

  • Barcode Scanner: Reads barcodes (a series of parallel lines of varying widths) by detecting the reflected light pattern. Used in retail for identifying products and prices.
  • Digital Camera: Captures images and videos as pixels. Each pixel stores colour and brightness information.
  • Keyboard: Converts key presses into electrical signals that the computer understands. Each key corresponds to a specific character or command.
  • Microphone: Converts sound waves into electrical signals. Used for voice input and recording.
  • Optical Mouse: Uses an LED or laser to detect movement across a surface. The movement is translated into cursor movement on the screen.
  • QR Code Scanner: Captures and decodes 2D QR codes (Quick Response codes). Can store more data than barcodes, including URLs and contact information.
  • Touch Screen: A display that also acts as an input device. Detects touch location.
    • Resistive: Uses pressure to detect touch. Less sensitive, but works with gloves.
    • Capacitive: Uses electrical charge to detect touch. More sensitive, but requires skin contact.

* **2D Scanner:** Captures a flat image of a document or object. Works by shining light on the object and measuring the reflected light. * **3D Scanner:** Captures the shape and dimensions of a physical object in three dimensions. Uses techniques like laser scanning or structured light. Produces a 3D model of the object.

Output Devices

• These devices allow the computer to output information to us.

• They are necessary for displaying results, playing sound, and controlling physical processes.

• Examples:

  • Actuator: Converts electrical signals into physical movement. Used to control motors, valves, robotic arms, etc.
    • Example: A motor turning a robotic arm.
  • DLP (Digital Light Processing) Projector: Uses tiny mirrors to project an image onto a screen. Produces sharp, bright images.
  • Inkjet Printer: Sprays tiny droplets of ink onto paper to create images and text. Relatively inexpensive.
  • Laser Printer: Uses a laser beam to create an image on a drum, which is then coated with toner (powdered ink). The toner is fused to the paper using heat. Produces high-quality prints quickly.
  • LED (Light-Emitting Diode) Screen: A display that uses LEDs to create images. LEDs emit light when an electric current passes through them. Bright and energy-efficient.
  • LCD (Liquid Crystal Display) Projector: Projects an image by passing light through an LCD panel.
  • LCD Screen: Uses liquid crystals to control the amount of light that passes through each pixel. Requires a backlight to illuminate the display.
  • Speaker: Converts electrical signals into sound waves.
  • 3D Printer: Builds three-dimensional objects layer by layer from a digital design. Uses materials like plastic filament, resin, or powder.

Sensors

• These devices detect physical properties and convert them into electrical signals.

• The electrical signals can then be processed by a computer.

• An ADC (Analogue-to-Digital Converter) is needed to convert the analogue signal to digital.

• Examples:

  Sensor	Data Captured	Typical Use
  Acoustic	Sound levels	Noise monitoring, voice recognition
  Accelerometer	Movement/tilt	Smartphones, fitness trackers, gaming consoles
  Flow	Liquid/gas flow rate	Industrial process control, medical equipment
  Gas	Presence and concentration of specific gases	Gas leak detection, air quality monitoring
  Humidity	Moisture content in the air	Weather stations, greenhouses
  Infra-red	Heat/movement	Security systems, remote controls
  Level	Liquid level in a container	Tank monitoring, industrial processes
  Light	Light intensity	Street lighting, camera light meters
  Magnetic Field	Magnetic field strength	Metal detectors, compasses
  Moisture	Water content in soil	Irrigation systems, agriculture
  pH	Acidity/alkalinity	Water treatment, chemical processes
  Pressure	Force per unit area	Weather stations, industrial processes
  Proximity	Distance to an object	Parking sensors, security systems
  Temperature	Heat level	Thermostats, weather stations

• Example Scenario and Sensor Choice:

  • Scenario: Designing a system to automatically control the temperature in a greenhouse.
  • Sensor Choice: A temperature sensor is the most suitable.
  • Justification: The temperature sensor will measure the air temperature inside the greenhouse. This data can then be used by a computer system to automatically adjust the heating or ventilation to maintain the optimal temperature for plant growth.

Exam Focus

• Specific Examples: Be prepared to give specific examples of how input/output devices and sensors are used in real-world applications.
• Justification: When asked to choose a sensor for a given scenario, always justify your choice. Explain why that sensor is the most appropriate for the task and what type of data it will collect.
• Analog vs. Digital: Understand the difference between analogue and digital data and the role of the ADC in sensor systems.
• Context is Key: Your answers should always be relevant to the specific context provided in the question. Avoid generic answers that don't address the prompt.
• Technical Terminology: Use correct technical terms in your answers.

Common Mistakes to Avoid

• ❌ Wrong: "A printer is an output device." ✓ Right: "A laser printer is an output device that uses a laser beam to create an image on a drum and then fuses toner to paper to produce high-quality prints quickly."
• ❌ Wrong: Describing a general use of a device. ✓ Right: Describing a use specific to the context of the question.
• ❌ Wrong: Providing an answer that isn't related to the context of the question. ✓ Right: Always consider the context and ensure your answer is relevant.
• ❌ Wrong: Saying digital data is used directly by sensors. ✓ Right: Sensors output analogue data, which needs to be converted to digital using an ADC.

Exam Tips

• Read the question carefully: Understand the specific requirements and context of the question before answering.
• Use precise language: Avoid vague or general statements. Use technical terms accurately.
• Justify your answers: Explain your reasoning and provide specific examples to support your claims.
• Practice with past papers: Review past exam questions to familiarize yourself with the types of questions that are asked and the level of detail that is expected.