CCEA A-Level Technology and Design AS 1 Electronic and Microelectronic Systems: a complete overview of the systems approach, sensors, switching, logic and timing

What this option demands

The AS Electronic and Microelectronic Systems option is the systems-and-control half of the AS year, studied alongside the design-and-manufacture core. It teaches you to design electronic products as input, process and output subsystems and to analyse the building blocks: sensors, switches, comparators, logic and timers. The examiners test the systems vocabulary, a set of standard calculations (potential divider, current gain, op-amp gain, LED resistor, 555 timing), and the reasoning behind drivers and protection.

This guide walks through the dot points of the option, then sets out the exam patterns CCEA repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

The systems approach and inputs

Every electronic product is modelled as input -> process -> output, drawn as a block diagram with arrows for signal flow, each block defined by its function so it can be designed and tested independently. Feedback returns output to the input for self-regulation (negative feedback in a thermostat gives closed-loop control). Input transducers (LDR, thermistor, switches) feed a potential divider that converts a changing resistance into a changing voltage, with the wiring deciding whether the output rises or falls with the stimulus.

Processing: switching, comparing and logic

The bipolar transistor is a current-operated switch (small base current controls a large collector current, $h_{FE} = I_C/I_B$), and the MOSFET is its voltage-controlled counterpart; inductive loads need a flyback diode. The operational amplifier compares two voltages as a comparator (switching when a sensor crosses a reference) and amplifies with a gain of $-R_f/R_{in}$ (inverting) or $1 + R_f/R_{in}$ (non-inverting). Logic gates (AND, OR, NOT, NAND, NOR, EOR) and Boolean algebra build combinational decision-making, with NAND and NOR universal.

Timing and outputs

The RC time constant ($\tau = RC$) underlies the 555 timer, used as a monostable (one pulse of $t = 1.1RC$ per trigger) or an astable (a continuous square wave at $f = 1.44/((R_1 + 2R_2)C)$). Output transducers (LED, lamp, buzzer, motor, relay, solenoid) are driven through transistors, MOSFETs or relays, with an LED current-limiting resistor of $R = (V_s - V_{LED})/I$ and isolation provided by a relay for mains loads.

How this option is examined

A typical CCEA profile for the electronics option:

• Calculation. Potential divider, current gain and base current, op-amp gain, LED resistor, and 555 monostable/astable timing.
• Logic. Truth tables, Boolean expressions and designing combinational logic from a word problem.
• System design. Block diagrams, choosing drivers, and explaining feedback.
• Reasoning. Why current-limiting resistors, base resistors, flyback diodes and relays are needed.

Check your knowledge

A mix of calculation and recall questions covering the option. Attempt them, then check against the solutions.

1. Name the three core subsystems in the systems approach. (3 marks)
2. A potential divider has a 4 kilohm fixed resistor in series with a 4 kilohm sensor across 10 V, output across the sensor. Find the output voltage. (2 marks)
3. A transistor passes 100 mA with hFE = 50. Find the base current. (2 marks)
4. State the inverting amplifier gain formula. (1 mark)
5. Complete the truth table output for a two-input AND gate for (0,0),(0,1),(1,0),(1,1). (2 marks)
6. A 555 monostable has R = 100 kilohm, C = 1 microfarad. Find the pulse length. (2 marks)
7. An LED (forward voltage 2 V, 20 mA) runs from 6 V. Find the series resistor. (2 marks)
8. Why is a flyback diode fitted across a relay coil? (2 marks)