How does the systems approach break an electronic product into input, process and output subsystems?
Electronic systems and subsystems: the systems approach with input, process and output blocks, block diagrams and signal flow, and analogue versus digital signals.
An Eduqas GCSE Electronics answer on the systems approach: representing an electronic product as input, process and output subsystems, drawing and reading block diagrams, tracing signal flow, and telling analogue and digital signals apart.
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What this dot point is asking
Eduqas wants you to describe an electronic product using the systems approach: split it into input, process and output subsystems, draw and read a block diagram, trace the signal flow through it, and tell analogue and digital signals apart. This way of thinking runs through the whole course and is exactly the model the non-exam assessment rewards.
The answer
The systems approach
Block diagrams and signal flow
Transducers
Analogue and digital signals
Examples in context
The input-process-output model is the backbone of every system in this course. A burglar alarm, a temperature controller, a light-sensitive porch light, a reaction-timer game and a digital counter are all designed by choosing an input subsystem, a process subsystem and an output subsystem and joining them. In the non-exam assessment you are explicitly marked on identifying subsystems, drawing the system block diagram, and testing each block in turn.
Try this
Q1. Name the three subsystems in the systems approach, in order. [1 mark]
- Cue. Input, process, output.
Q2. State what an input transducer does and give one example. [2 marks]
- Cue. It converts a physical quantity into an electrical signal, e.g. an LDR converts light into a change of resistance.
Q3. A microphone feeds a circuit. Is its output analogue or digital? Explain. [2 marks]
- Cue. Analogue: the voltage varies smoothly and can take any value as the sound pressure changes.
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 20194 marksAn automatic security light switches a lamp on when it gets dark and someone moves nearby. Draw a block diagram of this system, labelling the input, process and output subsystems.Show worked answer →
The block diagram is a left-to-right chain of three labelled boxes joined by arrows that show signal flow.
Input subsystem: a light sensor (light-dependent resistor in a potential divider) and a movement sensor (passive infrared), feeding the process block. Award a mark for naming sensible input transducers.
Process subsystem: a decision circuit (for example a comparator plus a logic gate) that turns the lamp on only when it is dark AND movement is detected. Award a mark for a process block that combines the two inputs.
Output subsystem: a driver (transistor) switching the lamp. Award a mark for a sensible output and its driver.
The final mark is for arrows pointing input then process then output, showing the direction of signal flow. Markers reward the three correctly labelled blocks and the correct signal-flow direction.
Eduqas 20212 marksState one difference between an analogue signal and a digital signal, and give one example of each in an electronic system.Show worked answer →
Difference (1 mark): an analogue signal can take any value within a range and varies smoothly (continuously), whereas a digital signal has only two valid levels, usually called logic 0 (low) and logic 1 (high).
Examples (1 mark for a matched pair): an analogue signal is the smoothly varying voltage from a microphone or a temperature sensor; a digital signal is the on or off output of a switch, a logic gate, or a microcontroller pin.
Markers reward a clear continuous-versus-two-level distinction and one correct example of each.
Related dot points
- Circuit concepts: charge, current, voltage (potential difference) and resistance, their units, and Ohm's law relating voltage, current and resistance.
An Eduqas GCSE Electronics answer on the core circuit concepts: charge and current, voltage as energy per coulomb, resistance, their units, and applying Ohm's law to find voltage, current or resistance in a circuit.
- Sensing subsystems: light-dependent resistors and thermistors, their resistance behaviour, and building light and temperature sensing circuits with potential dividers.
An Eduqas GCSE Electronics answer on sensing subsystems: how a light-dependent resistor and an NTC thermistor change resistance, and how to build light and temperature sensing circuits with potential dividers, including choosing which way round to put the sensor.
- Comparators: comparing two voltages, the reference set by a potential divider, the digital output, and using a comparator to make a sensing system switch at a threshold.
An Eduqas GCSE Electronics answer on comparators: how a comparator compares two input voltages and switches its output high or low, setting the reference with a potential divider, the digital nature of the output, and combining a sensor divider with a comparator to switch a circuit at a chosen threshold.
- Microcontrollers: the microcontroller as a programmable processing subsystem, inputs and outputs, and planning a control program with a flowchart.
An Eduqas GCSE Electronics answer on microcontrollers: the microcontroller as a programmable processing subsystem with input and output pins, the advantages of programming over fixed logic, and planning a control program with a flowchart using the standard symbols.
Sources & how we know this
- WJEC Eduqas GCSE (9-1) Electronics specification (C490) — WJEC Eduqas (2017)