IB Diploma Computer Science HL · Topic 7 — Control
Mini-Lesson
Control
Topic 7 looks at control systems: how sensors, processors and actuators work together, the difference between open and closed feedback loops, and how control can be centralised or distributed in the real world.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
Structure
Input, process, output
A control system follows the input to process to output pattern:
Input — sensors measure the physical world (temperature, light, pressure, motion).
Process — a microprocessor compares readings against target values and decides what to do.
Output — actuators (motors, heaters, valves) change the physical world.
Transducers
Sensors, transducers and actuators
A sensor detects a physical quantity; a transducer converts one form of energy into another (for example a physical quantity into an electrical signal). An actuator converts a control signal into physical action, such as a motor turning or a valve opening.
Quick check
Role of a sensor
?In a control system, what is the role of a sensor?
Quick check
Role of an actuator
?What does an actuator do in a control system?
Sort it
Input, output or control?
Tap a component, then the part of the control system it belongs to.
🌡️ Sensor (input)
⚙️ Actuator (output)
🧠 Processor / control
Feedback
Open and closed loops
Control can be open loop or closed loop:
Open loop — no feedback; the system does a fixed action regardless of the result (a simple timer).
Closed loop — uses feedback: the output is measured and fed back so the system self-corrects (a thermostat that switches the heater off when the target temperature is reached).
Quick check
Feedback loop
?A thermostat measures the room temperature and switches the heater off when the target is reached. This is an example of:
Distributed
Centralised and distributed control
In centralised control one processor makes all the decisions — simple, but a single point of failure. In distributed control, many processors cooperate — more robust and scalable, but harder to coordinate. Autonomous agents (robots, self-driving vehicles) sense and act on their own within their environment.
Quick check
Distributed control
?What is one advantage of distributed control over centralised control?
Applications
Real-world control systems
Everyday control systems include traffic lights, central heating, washing machines, automatic doors, lifts, irrigation and GPS navigation. Large industrial plants use SCADA to supervise and control processes over a wide area. Each has social and ethical implications for safety and reliability.
Match it
Match the system to its sensor
Tap a control system on the left, then the sensor it relies on.
Control system
Key sensor
Micro
Microprocessors and microcontrollers
A microprocessor is a general-purpose CPU on a chip. A microcontroller combines a processor, memory and input/output on a single chip, designed for one embedded control task — cheap, low-power and reliable, which is why they run washing machines, cars and appliances.
Quick check
Microcontroller
?Why are microcontrollers well suited to embedded control systems?
Ethics
Social and ethical impacts
Automated control systems raise safety and reliability concerns: a fault in a medical, aircraft or traffic system can be dangerous, so they need thorough testing, fail-safes and redundancy. There are also impacts on employment and on privacy where sensors collect data.
Quick check
Safety-critical
?A control system that manages hospital life-support must above all be:
Recap
The big ideas to know
Structure: input (sensors) to process (microprocessor) to output (actuators)
Transducer: converts one energy form to another
Loops: open (no feedback) vs closed (feedback, self-correcting)
Control: centralised (single point of failure) vs distributed (robust)