Exercises: Sensors, controllers and actuators

Name the three basic components of a control system and explain what each one does using the example of a heating thermostat.

Classify these components into sensors, actuators, and controller: a light sensor (LDR), a motor, a buzzer, a microcontroller board, a push button, and a servomotor. Justify each classification based on what the component does.

The figure shows the chain of a control system, but the central block is missing. State what block this is, what it does, and write the complete chain (with concrete examples for each block) for an automatic garage door.

Classify these elements as sensors or actuators and justify each decision: microphone, speaker, camera, light bulb, motion sensor, and relay that switches on a motor.

Explain what a microcontroller board does within a control system using the analogy of a "brain": what comes into it, what it does with it, and what commands it outputs.

Choose a control system in your home (heating, automatic staircase light, smoke detector with alarm...) and complete its chain: sensor → controller → actuator.

What is the difference between a temperature sensor and a full thermostat? Explain which components the sensor lacks to be a control system.

An irrigation system has a soil moisture sensor and a solenoid valve. Which component is missing for it to operate automatically, and what simple rule would it execute?

A smart plant pot waters the plant when the soil is dry. Identify the sensor, controller, and actuator of this system and explain what information passes from one component to another.

A standard fan runs until you switch it off, but an air conditioner stops and starts by itself to maintain the temperature. Explain the difference between both systems using the concept of feedback: which one re-measures the result of its action?

A traffic light operates on fixed timings, whether cars pass or not. Does this control system have sensors? What sensor would you add to make it "smart", and how would that change improve it?

A line-following robot uses two infrared sensors positioned on either side of the line. Explain what information each sensor provides and how the controller decides whether to turn left or right.

Explain the difference between an "on-off" actuator (e.g. a relay) and a proportional actuator (e.g. a servomotor), and give a suitable application for each type.

A car park counts vehicles using a sensor at the entrance and another at the exit. Design the controller logic to determine how many spaces remain free and what the entrance display panel should show when it becomes full.

The figure shows a control system with feedback, with the comparator point marked with ?. Explain which two values are compared at this point, what result is obtained, and how the controller uses it.

A thermostat reads $2\ ^\circ\text{C}$ higher than actual due to being out of calibration. Explain why the controller "believes" it is performing its job perfectly while the room remains colder than desired, and state the implications for sensor maintenance.

Analyse the full control chain of a push-button pedestrian crossing: what it detects, decides, and actuates at each stage, and explain what happens if the button sensor fails and what failsafe behaviour the system should have.

Design a system that maintains a school greenhouse between $18\ ^\circ\text{C}$ and $25\ ^\circ\text{C}$: select the sensors and actuators and describe the controller's decision logic using clear rules (if..., then...).

A classmate states: "To know with complete certainty whether a garage door has reached the end of its travel when closing, it is much better to use a photoresistor (LDR) than a mechanical limit switch, because being analog it gives us infinite values and much more information than a simple on-off digital sensor".

1. a) Technically refute this statement: explain two real operating or reliability issues that the LDR would cause in this task compared to the limit switch.
2. b) Justify why the digital sensor is superior in this specific case despite providing less data.
3. c) Design a function in the same automatic door where using the LDR is indeed the appropriate option and the limit switch is useless.

Design a smart pedestrian crossing that extends the green signal duration if it detects people still crossing slowly. Specify the sensors, decision rules, and actuators, and discuss a potential risk or system misuse.

A greenhouse is equipped with a heater, a fan, and a motorised window. Prioritise the three actuators based on power consumption and safety, and write the controller's decision rules for readings of $15\ ^\circ\text{C}$, $22\ ^\circ\text{C}$, and $30\ ^\circ\text{C}$.

To cool a server cabinet, threshold control (on-off) is tested: when the temperature exceeds $25,0\ ^\circ\text{C}$, the fan turns on at $100\ \%$; if it drops below $24,9\ ^\circ\text{C}$, it suddenly turns off.

1. a) Predict the negative consequences of this system on the room temperature and on the lifespan of the fan (continuous switching effect and mechanical wear).
2. b) Design a linear proportional control alternative between $20,0\ ^\circ\text{C}$ (fan at $0\ \%$) and $30,0\ ^\circ\text{C}$ (fan at $100\ \%$). Calculate what power percentage the fan will operate at if the temperature is at $26,5\ ^\circ\text{C}$.
3. c) Justify why this proportional control improves thermal stability and efficiency compared to threshold control.

Analyse the control system of a traffic light with cameras that gives priority to city buses: what it detects, decides, and actuates in each case, and what should happen if an emergency ambulance approaches.

An ultrasonic distance sensor fails with fabrics and angled surfaces. Explain what this implies for a robot that blindly "trusts" it, and propose a redundancy solution (combining sensors or cross-checks).