Programming Controller Boards

Explain what an algorithm is and what a program is, and what difference there is between describing it in pseudocode (using words) and with visual blocks.

The program instructions for a set of traffic lights are out of order: (a) wait 2 seconds, (b) turn on the red light and turn off the others, (c) turn on the green light and turn off the others, (d) return to the start, (e) wait 8 seconds (appears twice in the cycle), (f) turn on the amber light and turn off the others. Put them in the correct order and describe what the complete program does.

Explain what "reading an input" means in a control program and what difference there is between reading a push button (which gives 0 or 1) and reading a light sensor (which gives a number within a range).

Explain what a conditional statement ("if... then... else...") is and write the condition needed for these two warnings: an alarm that sounds when a door opens and an alert that beeps when the temperature exceeds $40\ ^\circ\text{C}$.

A car park barrier should only raise when a car is waiting (sensor) and the driver has also taken the ticket (push button); it lowers once the car has passed (a second sensor). Write the complete pseudocode for the cycle, combining both conditions at once.

What is the purpose of the "wait" command (a delay) in a control program? Give two examples in which, without that delay, the system would not perform its function.

Explain why almost all programs for controller boards contain a loop ("repeat forever") and describe what a set of traffic lights would do if its program did not have a loop.

In a pedestrian light system, the program reads the push button only once during each 30-second cycle. Explain what the pedestrian experiences upon pressing it and reason why long delays within the program affect the response speed of the system.

The flowchart in the figure controls a car park entry barrier, but the question inside the decision diamond is missing. Write the condition that should be checked there and describe the complete behaviour of the barrier.

To automate the watering of a school garden, an analog moisture sensor and an electric pump are available. A first program applies this rule: "repeat forever: if moisture < 30,0 %, turn pump on; else, turn pump off; wait 1 second".

1. a) If the sensor reading rapidly fluctuates between 29,8 % and 30,2 % due to localized absorption or electrical noise, predict how the electric pump will behave and what mechanical and electrical consequences it will have.
2. b) Explain why replacing the wait with "wait 10 minutes" does not guarantee optimal watering either (analyze the delay in water infiltration and the risk of over-irrigation).
3. c) Design a solution using hysteresis control: define two different logical moisture thresholds (start and stop) and write the structured pseudocode or describe in detail the corresponding flowchart, justifying why it prevents constant switching.

Write in pseudocode the complete program for a simple set of traffic lights: green for 8 seconds, amber for 2, red for 8, and repeat. Indicate at each step which lights are on and which are off.

To control a vehicle traffic light that includes a pedestrian demand push button, two programming structures are compared:

• Option A (linear sequential): loop with successive blocking calls wait(t) (green 30 s, amber 3 s, red 15 s).

• Option B (state machine): the system remains in the CARS_GREEN state and only transitions state if the pedestrian push button signal is detected.

1. a) Justify why Option A is inadequate to respond immediately to a pedestrian pressing the button and what response flaw it will cause.
2. b) If you are asked to add a new function ("the pedestrian green light must flash 3 times for 3,0 s before turning red, but only if the sensor for visually impaired people is not active"), explain what modularity and maintenance advantages Option B presents compared to Option A.
3. c) Design the state diagram or general pseudocode for Option B, clearly identifying the states, input events, and actions associated with each transition.

A program counts cars: "repeat forever: wait for sensor to change from 0 to 1; add 1 to cars variable". Explain what it does, what purpose it serves, and what problem arises if a car stops right over the sensor.

A fan control program states: "if temperature is greater than $26\ ^\circ\text{C}$, turn off fan; if less than $26\ ^\circ\text{C}$, turn on fan". Describe the actual behaviour of the fan and write the corrected program.

The control system of an automatic toll barrier has a presence sensor 1 (just before the barrier) and a sensor 2 (just after). An operator proposes this code:

repeat forever:

    if (sensor_1 == DETECTED) then:

        raise_barrier()

    if (sensor_1 == CLEAR) then:

        lower_barrier()

1. a) Predict what accident will physically occur as soon as the front of the car passes sensor 1 if the rear part is still under the barrier. Justify why the operator's proposal to "add a 5,0 s pause before lowering" does not solve the problem with slow traffic or articulated vehicles.
2. b) Design in pseudocode a safe algorithm that uses both sensors to ensure that the barrier raises when the vehicle arrives, stays up as long as either of the two sensors detects presence, and only lowers when the vehicle has completely cleared sensor 2.