Ch 2 · 3.2 Input and Output Devices · O Level Computer Science 2210
Topic 2 of 4 in Hardware — O Level Computer Science 2210 — 39 lessons.
Introduction
A computer is useless if it cannot take in data or give out results. Input devices, output devices and sensors connect a computer to people and to the real world. (Syllabus section 3.2.)
Key ideas — Input devices
An input device allows data to be entered into a computer (from a user or the environment) and converts it into a form the computer can process (binary). Without input, the computer has nothing to process.
🧑🏫 Teacher's explanation
Think of a computer like a human brain. A brain is useless if it cannot see, hear, or feel anything from the outside world. Input devices are the 'senses' of the computer. They take physical phenomena—like the sound of your voice, the light hitting a lens, or the pressure of your finger—and translate them into binary code (0s and 1s) that the processor can actually understand.
📖 Definitions
🔍 Worked example — Easy
A user wants to input a digital image of a physical photograph into a computer. Identify the most suitable input device and explain how it converts the image into digital data.
🔍 Worked example — Standard
Compare the suitability of a resistive touch screen versus a capacitive touch screen for a device used by a construction worker wearing thick industrial gloves.
🔍 Worked example — Exam-style
A smart greenhouse needs to monitor the moisture level in the soil to automate irrigation. Identify the most suitable sensor and explain the data it captures.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Identify the most suitable sensor for this task. [1] (b) Describe how the sensor provides data to the computer system. [2] (c) The system must trigger a cooling fan if the temperature exceeds 80^° C. Identify the type of device that would be required to physically turn on the fan. [1] [4 marks]
Key ideas — Output devices
An output device receives data from a computer and converts it into a form that is useful to the user or controls something (on screen, on paper, as sound or movement). It lets the results of processing be seen, heard or used.
🧑🏫 Teacher's explanation
Think of a computer as a brain. A brain can think all day, but if it can't tell you what it's thinking or move your arm to do something, it is useless to the outside world. Output devices are the 'mouth' and 'hands' of the computer.
📖 Definitions
🔍 Worked example — Easy
A user needs to print a high-quality, professional photograph for a gallery. Which output device is most suitable: a laser printer or an inkjet printer? Explain why.
🔍 Worked example — Standard
A smart greenhouse system needs to increase the temperature when it falls below 18^° C. The computer sends a signal to a component to physically open a heating vent. Identify the type of output device required.
🔍 Worked example — Exam-style
Compare an LCD screen and an LED screen in terms of how they produce light/images.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Identify the type of output device used to open the vent. [1] (b) Describe how a 3D printer produces a solid object. [2] [3 marks]
Key ideas — Sensors
A sensor is an input device that measures a physical property of the environment and sends the data to a computer (via an analogue-to-digital converter if the reading is analogue). Sensors are used in monitoring and control systems, to collect data automatically and continuously, even in dangerous places.
🧑🏫 Teacher's explanation
Imagine you are trying to bake a cake, but you are in a different room. You can't see the oven, so you use a thermometer to check the heat and a timer to check the time. In computer science, a sensor acts like that thermometer. It 'feels' the physical world and turns that feeling into digital data that a computer can understand.
📖 Definitions
🔍 Worked example — Easy
A greenhouse needs to maintain a constant temperature. Identify the most suitable sensor and state whether it is used for monitoring or control if it only records the temperature every hour.
🔍 Worked example — Standard
A smart car uses a sensor to detect how close it is to a wall to prevent collisions. Identify the sensor and explain why a 'level' sensor would be inappropriate.
🔍 Worked example — Exam-style
A factory uses a sensor to detect if a gas leak has occurred. The sensor detects the presence of Carbon Monoxide. Name the sensor and describe the full system loop required to ensure safety.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) Identify one sensor that would be used to monitor the amount of water in the soil. [1] (b) The greenhouse also needs to control the temperature. Describe how a sensor and an actuator would work together to maintain a constant temperature. [3] [4 marks]
Worked example
Explain why a capacitive touch screen is suitable for a smartphone but a resistive screen may be better for a factory control panel.
🔍 Worked example — Easy
Identify the most suitable sensor for a system designed to monitor the amount of water in a tank to prevent overflow.
🔍 Worked example — Standard
A technician needs to monitor the concentration of a specific chemical in a liquid solution. Which sensor should be used?
🔍 Worked example — Exam-style
Compare the suitability of a capacitive touch screen and a resistive touch screen for a device used by construction workers in a dusty, outdoor environment wearing heavy gloves.
⚠️ Common errors
Common mistakes
Practice
Answers: (1) To allow data to be entered into a computer and converted into a form it can process. (2) A laser builds an image of the page as electric charge on a drum; toner sticks to the charged areas and is transferred to paper, then fused with heat. (3) Advantage: works with any object or gloves, and is cheap; disadvantage: less clear, less responsive, can be scratched or damaged, no multi-touch. (4) (a) pressure (or magnetic field); (b) light; (c) moisture. (5) An output device that causes physical movement, such as a motor or valve, in a control system.