AQA GCSE Engineering: Systems, a complete overview of input-process-output, mechanisms, electronics and programmable control

What the systems topic demands

Engineered products are systems: they take something in, do something with it, and produce a useful result. The systems topic teaches you to describe any product in those terms and to recognise the mechanical, electronic and programmable building blocks inside it. AQA tests recall of components and mechanisms alongside application: choosing the right building block for a job and doing simple calculations such as gear ratios. This overview ties together the four dot-point pages in the topic.

The input-process-output model and feedback

The input-process-output (IPO) model breaks any system into inputs (energy or signals entering), a process (the action done to them) and outputs (the useful result). Feedback sends information about the output back to the input so the system can self-correct. A system with feedback is a closed loop (a thermostat keeps a room at a set temperature); a system without feedback is an open loop (a timed toaster). Systems are drawn as labelled block diagrams with arrows showing the signal flow.

Mechanical systems and motion

The four types of motion are linear (straight line), rotary (turning), reciprocating (back and forth in a straight line) and oscillating (swinging along a curve). Mechanisms change the type, direction, speed or force of motion: levers and linkages change force and direction, gears and pulleys change rotary speed and torque, cams change rotary into reciprocating, and cranks change rotary into reciprocating and back. The key calculation is the gear ratio, the driven teeth divided by the driver teeth: a ratio above one slows the output but increases torque.

Electronic systems

Electronic systems follow the same IPO model. Inputs sense the world: switches, light-dependent resistors and thermistors, usually in a potential divider. Process components handle the signal: resistors set current, transistors switch, and logic gates (AND, OR, NOT) make decisions. Outputs do something useful: LEDs and lamps for light, buzzers for sound, and motors for movement. A frost alarm strings a thermistor, a transistor and a buzzer into a working system.

Programmable systems and control

A microcontroller is a programmable chip that forms the process stage: it reads inputs, runs a stored program and switches outputs. Control programs are planned as flowcharts using standard symbols (start/stop, process, decision and input/output). Programmable control beats fixed wiring because the behaviour is changed by reprogramming, one chip replaces many components, and complex decisions, delays and counting are easy in software.

Check your knowledge

A mix of recall and application questions covering the systems topic. Attempt them under timed conditions, then check against the solutions.

1. Name the three parts of the input-process-output model. (3 marks)
2. State the difference between an open loop and a closed loop system. (2 marks)
3. Name the four types of motion. (4 marks)
4. A driver gear of 20 teeth meshes with a 60-tooth gear. Calculate the gear ratio and state its effect on output speed. (3 marks)
5. Sort these into input, process and output: LDR, transistor, LED. (3 marks)
6. Name the flowchart symbol used for a yes/no decision. (1 mark)
7. State one advantage of a microcontroller over a fixed-wired circuit. (1 mark)