Sensors, controllers and actuators

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.

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.

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.

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.

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...).

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.

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.

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).