What do microcontroller systems cover in WJEC A-Level Electronics?

Microcontroller systems cover the architecture of a microcontroller (CPU, program and data memory, input/output ports and often an on-chip ADC), how to interface inputs and outputs (pull-up resistors for switches, transistor drivers and flyback diodes for relays and motors, analogue sensors through the ADC), and programming. Programming covers flowcharts, the structures of sequence, selection and iteration, input and output instructions, time delays, subroutines, and turning a system specification into a program.

How is an output device such as a relay connected to a microcontroller?

A microcontroller pin can supply only a small current, so a relay or motor is driven through a transistor (or MOSFET) switch with the load in the transistor's collector or drain circuit. A flyback diode is connected across an inductive load such as a relay coil to absorb the back-EMF produced when the current is switched off, which would otherwise damage the transistor. The pin simply turns the transistor on and off.

What are the three program structures used in microcontroller programming?

The three structures are sequence (instructions carried out one after another in order), selection (a decision, an if, that branches the flow depending on a condition such as whether a switch is pressed), and iteration (a loop that repeats a block of instructions, either a fixed number of times or until a condition is met). Any program can be built from these three, and flowcharts represent them with process boxes, decision diamonds and arrows.

What is a subroutine and why is it used?

A subroutine is a self-contained, named block of code that performs a specific task and can be called from anywhere in the program, returning to the point it was called from when it finishes. It is used to avoid repeating the same code (a task such as a time delay is written once and called many times, which saves program memory), to make the program easier to read and structure, and to make testing and maintenance easier because the block can be checked on its own.

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WJEC A-Level Electronics Microcontroller Systems: architecture, interfacing and programming explained

A deep-dive WJEC A-Level Electronics guide to Microcontroller Systems. Covers the architecture of a microcontroller (CPU, memory, ports), digital input and output ports, interfacing switches, sensors and output devices, the on-chip ADC, and programming with flowcharts, the structures of sequence, selection and iteration, input and output instructions, time delays and subroutines.

Generated by Claude Opus 4.813 min readWJECUpdated 2026-06-16

Reviewed by: AI editorial process; not yet individually human-reviewed

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What the microcontroller section demands
Microcontroller architecture and interfacing
Microcontroller programming
How the microcontroller section is examined
The topics, dot point by dot point
For the official specification

What the microcontroller section demands

The microcontroller is the programmable brain of most modern electronic products, and Component 2 (Application of Electronics) treats both its hardware (architecture and interfacing) and its software (programming with flowcharts). The topic rewards clear interfacing reasoning and well-structured program design.

This guide walks through the two topics in specification order, then sets out the exam patterns WJEC repeats. Each topic has a matching dot-point page with worked exam questions; this overview ties them together.

Microcontroller architecture and interfacing

A microcontroller is a small computer on a chip: a CPU that runs the program, memory for code and data, and input/output ports whose pins connect to the outside world, often with an on-chip ADC. Each pin is configured as a digital input or output. Switch inputs need a pull-up or pull-down resistor for a defined level; output devices needing more current than a pin can supply (relays, motors) need a transistor driver, with a flyback diode for inductive loads. Analogue sensors are read through the ADC, typically as the output of a potential divider.

Microcontroller programming

A program is built from three structures: sequence (ordered steps), selection (a decision that branches, an if), and iteration (a loop). Flowcharts show these with process boxes, decision diamonds and arrows. Programs read inputs, drive outputs, and use time delays for timing. A subroutine is a reusable named block called from anywhere, which saves memory and improves clarity. Designing a program means turning a worded specification into this structure of inputs, decisions, loops and outputs.

How the microcontroller section is examined

Expect interfacing questions (pull-up resistors, transistor drivers, flyback diodes, ADC inputs), the case for an on-chip ADC, flowchart design from a worded specification using the three structures, and the subroutine explanation. These are reliable marks built on clear structure and correct interfacing.

The topics, dot point by dot point

Each topic has a dot-point answer page with worked exam questions and cross-links. Browse them from this overview and the subject hub.

For the official specification

WJEC Eduqas publishes the full specification, past papers and mark schemes at eduqas.co.uk. Always revise from the current specification and the board's own past papers, because question style is board-specific.

Sources & how we know this

WJEC Eduqas GCE A-level Electronics specification — WJEC Eduqas (2017)