What input, process and output components are used in electronic systems, and what does each do?
Input, process and output components: switches and sensors (light-dependent resistors and thermistors) as inputs, transistors, integrated circuits and microcontrollers as process devices, and LEDs, buzzers and motors as outputs, with their functions and uses.
A focused answer to Eduqas GCSE Design and Technology (C600) on input, process and output components: switches, LDRs and thermistors, transistors, ICs and microcontrollers, and LEDs, buzzers and motors, with their functions.
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What this dot point is asking
Eduqas C600 expects you to know the components that fill each block of an electronic system: inputs (switches and sensors such as the LDR and thermistor), process devices (the transistor, integrated circuits and microcontrollers), and outputs (the LED, buzzer and motor). You need each component's function and use. In the written exam this is tested by short questions on what a sensor senses and by Explain questions on the role of a transistor and the need for a series resistor.
Input components
- Switches: push-to-make, push-to-break, toggle, reed (magnetic) and tilt switches detect a user action or a position.
- Light-dependent resistor (LDR): senses light. Its resistance is low in bright light and high in darkness, so it can detect day or night (a street light, a night light).
- Thermistor: senses temperature. Its resistance changes with heat (commonly falling as it warms), so it can detect hot or cold (a fire alarm, a thermostat).
Process components
The transistor is the key building block: a small current at its base switches a much larger current through it, so a weak sensor signal can switch a motor or lamp. ICs pack many components into one chip for a set function (a timer, an amplifier, logic). A microcontroller goes further, running a program that can make complex decisions and be reprogrammed, replacing many fixed parts.
Output components
- LED (light-emitting diode): gives light efficiently; it needs a series resistor to limit the current, or it will draw too much and burn out.
- Buzzer: gives an audible signal (an alarm, a confirmation beep).
- Motor: converts electricity into rotary movement (a fan, a pump, a robot wheel); high-current motors are usually switched by a transistor.
Try this
Q1. State what a thermistor senses. [1 mark]
- Cue. Temperature (its resistance changes with heat).
Q2. Give one reason an LED needs a resistor in series with it. [1 mark]
- Cue. To limit the current so the LED does not draw too much and burn out.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas C600 20192 marksState what a light-dependent resistor (LDR) senses and explain how its resistance changes.Show worked answer →
A 2-mark question, one mark for what it senses and one for how its resistance changes.
A light-dependent resistor (LDR) senses light level. Its resistance changes with the amount of light falling on it: in bright light its resistance is low, and in darkness its resistance is high.
This lets it act as an input that detects light or dark, for example switching a street light on when it gets dark.
Markers reward: an LDR senses light, and its resistance falls in bright light and rises in the dark. Saying it senses temperature (that is a thermistor) or getting the resistance change the wrong way round loses marks.
Eduqas C600 20224 marksAn electronic system uses a transistor as a process device. Explain the role of the transistor and why an LED needs a series resistor in the output.Show worked answer →
A 4-mark Explain wants the transistor's role and the resistor's purpose.
The transistor acts as an electronic switch in the process stage: a small current from the input (for example from a sensor) switches a much larger current on or off to drive the output, so a weak sensor signal can control a motor or lamp.
An LED needs a series resistor to limit the current through it: without the resistor the LED would draw too much current and burn out. The resistor sets a safe current so the LED lights reliably and lasts.
Markers reward: the transistor switches a large current using a small one (acting as a switch/amplifier in the process stage), and the resistor limits current to protect the LED. Missing either part caps the mark.
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Sources & how we know this
- WJEC Eduqas GCSE (9-1) Design and Technology (C600) specification — WJEC Eduqas (2017)