Input and output devices
Output devices are hardware components that convert digital data processed by the CPU back into a form that humans or other systems can understand or use. Without output devices, the results of computation would remain trapped inside the machine as electrical states.
Building on previous concepts, sensors typically produce an analogue signal (a continuous voltage that varies smoothly). To be processed by a digital computer, this signal must pass through an Analog-to-Digital Converter (ADC). An ADC samples the analogue voltage at regular intervals and converts each sample into a binary number. This is why understanding sensors requires knowledge of both the physical quantity they detect and the digital representation of that data.
| Function / What it detects |
|---|
| Detects key presses to input text and commands. |
| Detects position or touch coordinates for cursor control. |
| Detects sound waves (pressure variations) and converts them to electrical signals. |
| Uses a light sensor (CCD/CMOS) to capture images by detecting light intensity at each pixel. |
| Uses a light sensor (often infra-red or laser) to detect the pattern of reflected light from black and white bars. |
| Detects unique physical traits like fingerprints or iris patterns for security. |
| Function / What it produces |
|---|
| Displays visual information using pixels (LCD/LED). |
| Converts electrical signals into sound waves. |
| Produces a physical hard copy of digital documents. Common types include Inkjet (sprays ink) and Laser (uses toner and heat). |
| Provides simple visual status updates (e.g., power on/off). |
| Converts electrical signals into physical movement or force. Used in robotics, drones, and automated doors. |
Correction: Headphones are an external accessory, not a built-in component. For a tablet or smartphone, the correct built-in output device is the speaker. Similarly, do not list 'keyboard' or 'mouse' as built-in input devices for a touchscreen tablet; use touchscreen instead.
Correction: A microphone captures sound (input). An output device that produces sound is a speaker. Confusing these two is a common conceptual error.
Correction: An actuator creates physical movement (e.g., moving a drone's propeller or opening a door). It does not produce visual information. Visual output is handled by screens or projectors.
Why examiners accept this: Examiners look for specificity. Generic answers like 'a sensor' or 'motion sensor' are often insufficient. You must name the specific technology and explain its suitability based on range, sensitivity, or environmental constraints.
Correct Usage Example:
Question: Select a suitable sensor to detect if a door is open in a dark room.
Answer: A Passive Infra-Red (PIR) sensor is suitable because it detects changes in infrared radiation (heat) emitted by moving bodies. It works effectively in the dark as it does not rely on visible light, unlike a light-dependent resistor (LDR).
Why examiners accept this: You must address limitations. For example, explain why an LDR is NOT suitable for measuring temperature (it responds to light, not heat).
Correct Usage Example:
Question: Why is a thermistor used in a fire alarm instead of a microphone?
Answer: A thermistor is used because it detects changes in temperature, which is the primary indicator of fire. A microphone detects sound, which may not be present during the early stages of a fire or may be caused by non-fire events (false positives).