The Three Components: Sensors, Microprocessor, Actuators — Automated Systems | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 3% of your exam marks.

stable

Rare

Stable3%

Sensor to microprocessor to actuator control loop questions. Usually 3 to 4 marks.

Every automated system, no matter how simple or complex, is built from the same three kinds of part:

Component	What it does	Direction
Sensors	Measure a physical property of the environment (temperature, light, movement, pressure, etc.) and convert it into a digital signal	Input to the system
Microprocessor	Receives the sensor readings, compares them against pre-programmed rules or thresholds, and decides what (if anything) to do	Processing
Actuators	Receive instructions from the microprocessor and turn them into a physical action (motor turning, valve opening, alarm sounding, heater switching on)	Output from the system

The pipeline

The three components form a clear input-process-output pipeline:

→ →

The sensor measures the relevant physical quantity (e.g. temperature) and sends a digital reading to the microprocessor.
The microprocessor compares the reading against the rules in its program (e.g. "if temperature < 20 °C, switch on heater") and decides what to do.
If action is needed, the microprocessor sends a control signal to an actuator, which performs the physical change (e.g. turns on the heater motor or opens a valve).

Many sensor types appeared in topic 8 (Input and Output Devices); each one of those sensors can be the input side of an automated system. Common actuators include motors, servos, valves, relays, heaters, pumps, alarms and buzzers.

Exam tip

Explaining how sensor, microprocessor and actuator work together

What comes up: A scenario describes an automated system (a train door, a self-driving vehicle, a greenhouse, etc.) and asks you to explain how the sensor, microprocessor and actuator are used in that context. These questions typically carry 4–6 marks, so you need the full cycle.

Write (five to six marks): Work through the pipeline in order:

Name the appropriate sensor type (proximity, infrared, temperature, etc.) and state that it continuously measures the relevant quantity and sends a digitised reading to the microprocessor.
The microprocessor compares the reading against a stored/preset value (threshold).
If the condition is met (e.g. an object is within 3 m), the microprocessor sends a signal to the actuator to trigger the action (e.g. stop the motor, close the door).
If the condition is not met, (or the actuator is not activated).