Input and output devices Revision Notes

Input devices are hardware components that allow users to enter data and instructions into a computer system. Without input devices, a computer cannot receive information from the outside world, making interaction impossible. They translate physical actions, such as pressing keys or scanning images, into digital signals that the computer can process.

For example, a keyboard converts key presses into binary codes representing letters or commands. This conversion is essential because computers operate using binary data, not physical actions. Therefore, input devices serve as the bridge between human users and computer processing units.

• Input devices enable data and command entry into computers.
• They convert physical user actions into digital signals.
• They are essential for user-computer interaction.

Several input devices are widely used, each designed for specific types of data entry:

Keyboards allow users to input text and commands by pressing keys.

Optical mice detect movement and button clicks to control the cursor on the screen, converting physical motion into pointer movement data.

• Keyboard: text and command input via keys.
• Optical mouse: detects movement and clicks for cursor control.

Scanning devices capture visual information and convert it into digital data:

Barcode scanners read patterns of black and white lines representing product information, commonly used in retail for quick identification and pricing.

QR code scanners read two-dimensional codes that can store more complex data such as URLs or contact details, often used in marketing and ticketing systems. These scanners use cameras or laser sensors to interpret the code pattern quickly and accurately.

• Barcode scanners read linear codes for product data.
• QR code scanners read 2D codes for complex data.
• Digital cameras capture images as input for processing or storage.

Touch screens combine input and output functions by allowing users to interact directly with what is displayed. There are three main types:

Resistive touch screens consist of two flexible layers separated by a gap. When pressed, the layers touch, changing the electrical current and detecting the touch location. They work with any object, including a stylus or gloved finger.

Capacitive touch screens use the electrical properties of the human body. They have a layer that stores electrical charge; touching the screen changes the charge at that point, which the device detects. These screens support multi-touch gestures but require a conductive touch, like a bare finger or special stylus. They are common in smartphones and tablets due to their responsiveness and clarity.

• Resistive: pressure-based, works with any pointer.
• Capacitive: detects electrical charge changes, supports multi-touch.
• Infra-red: uses light beams to detect touch without screen contact.

2D scanners capture flat images, such as photographs or documents, by converting reflected light into digital images. They are commonly used for digitising printed materials.

3D scanners capture the shape and dimensions of physical objects by measuring the distance between the scanner and the object's surface at many points. This data creates a digital 3D model, useful in manufacturing, design, and medical applications.

Both types convert physical visual information into digital data but differ in dimensionality and application scope.

• 2D scanners digitise flat images.
• 3D scanners create digital models of physical objects.
• 3D scanning involves measuring spatial coordinates for each point on an object.

Output devices are hardware components that receive data from a computer's processing unit and convert it into a form perceivable by humans or other systems. Without output devices, users would not be able to see, hear, or otherwise interpret the results of computer operations.

They are necessary because computers process data internally as binary code, which is not directly understandable. Output devices translate this data into visual, auditory, or physical forms, enabling interaction and communication.

For example, after typing a document, an output device like a printer or screen allows you to see the text. Similarly, speakers output sound data so you can hear audio files or alerts.

• Output devices convert processed data into human-understandable forms.
• They enable communication between the computer and the user or other systems.
• Without output devices, computer results would remain inaccessible.

Output devices vary depending on the type of output required: visual, auditory, or physical. Common categories include screens, printers, speakers, projectors, actuators, and 3D printers.

Screens (such as LED and LCD) display images, text, and videos. Speakers output sound. Printers produce physical copies of digital documents or images. Projectors enlarge images or videos onto surfaces for group viewing. Actuators convert electrical signals into physical movement. 3D printers create three-dimensional objects from digital models.

• Screens (LED, LCD) show visual information.
• Speakers produce audio output.
• Printers (inkjet, laser) create physical copies on paper.
• Projectors (DLP, LCD) display enlarged images on surfaces.
• Actuators perform physical actions based on computer signals.
• 3D printers build physical objects layer by layer.

Printers are output devices that produce hard copies of digital documents or images. Two common types are inkjet and laser printers.

Inkjet printers spray tiny droplets of ink onto paper. They are suitable for high-quality colour images and photos but tend to be slower and have higher running costs due to ink consumption.

Laser printers use a laser beam to form an electrostatic image on a drum, which attracts toner powder and transfers it to paper. They are faster, better for high-volume printing, and produce sharp text but are generally more expensive initially and less effective for photo-quality colour prints.

• Inkjet printers: good for colour images, slower, higher ink cost.
• Laser printers: faster, better for text, higher initial cost.
• Choice depends on printing needs: volume, quality, and cost.

LED (Light Emitting Diode) and LCD (Liquid Crystal Display) screens are common output devices for visual information.

LED screens use light-emitting diodes to produce bright, energy-efficient displays with good colour and contrast.

LCD screens use liquid crystals that modulate light to form images, often requiring a backlight. They are widely used in monitors and laptops due to their thinness and clarity. Projectors enlarge images onto surfaces for presentations or entertainment. DLP (Digital Light Processing) projectors use microscopic mirrors to reflect light and create images, offering sharpness and contrast. LCD projectors pass light through liquid crystal panels to form images, generally producing brighter colours but sometimes less contrast.

• LED screens: bright, energy-efficient, good contrast.
• LCD screens: use liquid crystals, require backlight, thin design.
• DLP projectors: use mirrors, sharp images, good contrast.
• LCD projectors: use liquid crystals, brighter colours, less contrast.

Speakers convert electrical signals into sound waves, allowing users to hear audio from computers, such as music, alerts, or speech.

Actuators are output devices that convert electrical signals into physical movement or action. For example, a robotic arm controlled by a computer uses actuators to move.

3D printers build physical objects by adding material layer by layer based on digital designs. They are used in prototyping, manufacturing, and education to create complex shapes that would be difficult to produce otherwise.

• Speakers output sound from digital audio data.
• Actuators perform physical movements controlled by computers.
• 3D printers create three-dimensional objects from digital models.

A sensor is a device designed to detect and measure a physical property from the environment and convert it into a signal that can be interpreted by humans or machines. This signal is often electrical but can be any form of data output. Sensors enable systems to monitor conditions, respond to changes, and collect data for analysis.

The primary purpose of sensors is to provide accurate and timely information about physical phenomena such as temperature, pressure, or motion. This information is essential in automation, safety systems, environmental monitoring, and many other applications.

For example, a temperature sensor in a thermostat detects room temperature and sends a signal to control heating or cooling systems to maintain a desired temperature.

• Sensors convert physical properties into readable signals.
• They enable monitoring and control in various systems.
• They are essential for data collection and automation.

Sensors vary widely depending on the physical property they measure. Understanding the type of data each sensor collects helps in selecting the right sensor for a task.

Acoustic sensors detect sound waves and convert them into electrical signals. They are used in applications like voice recognition or noise level monitoring.

Accelerometers measure acceleration forces, including gravity, and are used in devices like smartphones to detect orientation or in vehicles for crash detection systems. They provide data on movement and vibration intensity and direction.

• Acoustic sensors measure sound waves.
• Accelerometers measure acceleration and vibration.
• Flow sensors measure the rate of fluid movement.
• Gas sensors detect the presence and concentration of gases.
• Humidity sensors measure moisture levels in the air.
• Infra-red sensors detect heat radiation and are used in motion detectors.
• Level sensors measure the height of liquids or solids in containers.
• Light sensors measure light intensity, useful in automatic lighting systems or cameras.

Magnetic field sensors detect magnetic forces and are used in compasses or to detect metal objects.

Moisture sensors measure water content in soil or materials, important in agriculture.

pH sensors measure acidity or alkalinity of liquids, vital in chemical processing or water quality monitoring.

• Pressure sensors measure force per unit area, used in weather stations or vehicle tyre pressure monitoring.
• Proximity sensors detect the presence or absence of an object without physical contact, common in smartphones and industrial automation.
• Temperature sensors measure heat levels and are widely used in climate control, manufacturing, and healthcare.

Choosing the right sensor depends on the physical property to be measured, the environment, accuracy requirements, and cost constraints.

For example, to monitor water quality in a river, a combination of pH sensors (to measure acidity), temperature sensors (to monitor water temperature), and flow sensors (to measure water speed) might be used.

In a security system, infra-red sensors are suitable for detecting human movement because they detect heat emitted by bodies, while proximity sensors can detect when doors or windows are opened.

• Match sensor type to the physical property to be measured.
• Consider environmental conditions such as temperature range and exposure to elements.
• Evaluate accuracy and response time needed for the application.
• Balance cost against performance requirements.

A smartphone uses accelerometers to detect orientation changes and acoustic sensors for voice input.

Weather stations use humidity, temperature, pressure, and light sensors to collect environmental data.

Industrial automation employs proximity sensors to detect object positions and flow sensors to monitor liquid movement in pipes.

• Sensors enable smart device functionality.
• Environmental monitoring relies on multiple sensor types.
• Automation systems use sensors for precise control and safety.