A microcontroller executes a program and communicates with physical inputs and outputs. We retain variables, decisions and functions learned in Python but must adapt language, libraries and environment. In Arduino C++ for ESP32, setup() prepares the device at startup and loop() repeats while it operates. Braces delimit blocks, many statements end in semicolons and indentation helps readability. Copying a Python file does not convert it to C++.

A type describes what kind of data a variable handles. bool represents true or false; a constant declared with const must not be reassigned. The classroom timing pattern uses unsigned long. A void function returns no value to its caller, although it can perform an action such as Serial.println(). Defining a function does not execute it: a call with arguments is needed. A serial message reports program behaviour but does not demonstrate physical movement. Separating information from actuation lets us test decisions before attaching a mechanism.

Power supplies energy; a signal communicates information. A module can have one power requirement and a different signal requirement. An ESP32 GPIO does not accept any voltage simply because the module connector says 5 V. Before assembly, consult the exact board, shield and component models to check compatibility, polarity and any required adaptation. Do not infer pins from resemblance to another board.

A shield connector number may differ from the GPIO number used in code. The assembly sheet maps both and states power, signal and a common GND reference where the validated interface requires it. A digital input represents HIGH or LOW; whether LOW means detection depends on the module. A pin without a defined level can float and change without real detection. Pull-up and pull-down help establish levels, but their use depends on the GPIO and circuit. Validate configuration against documentation before making connections with the system powered off.

Before a controller can decide, it needs inputs with an agreed meaning. pinMode configures a GPIO’s use, digitalRead obtains its digital level and digitalWrite sets the level of an output configured for that purpose. However, HIGH and LOW describe levels rather than complete situations. The adapter interprets the module’s polarity and supplies detection, stop and validity to the logic. An analogue reading also requires its range, resolution and relationship to the measured quantity: naming a raw value distance does not turn it into centimetres.

This translation separates reading inputs, deciding the state and applying the output. The logic works with stable meanings, while the adapter contains hardware details. It can therefore be checked first with known conditions generated through serial. Command 1 enables detection and 0 removes it; p enables stop, r releases it and x simulates invalidity. These test inputs allow a sequence to be repeated. When the sensor is introduced, its signal must be checked against the expected meaning.

Each test establishes one part of that path. Simulating invalidity checks the logic’s response but adds no ability to discover a physical fault. The basic digital reader does not automatically identify a disconnected cable; that diagnosis needs an additional validated check. Likewise, receiving correct detection does not yet demonstrate mechanism movement. Output starts disabled and is applied after the state is decided, allowing the different conditions to be resolved before issuing a command and avoiding contradictory actions.

A state summarises a previous situation that matters for the current decision. REPOSO, DETECTADO, ACTUANDO and PARADO represent situations of the same controller, not different devices. A transition relates current state, condition and next state. REPOSO becomes DETECTADO when valid detection begins; DETECTADO keeps checking while detection continues and becomes ACTUANDO when the interval is met. If detection disappears earlier, it returns to REPOSO and that verification is lost.

Stopping or an invalid reading takes priority and leads to PARADO from any state, disabling output. Releasing stop and recovering validity does not resume an old actuation: if detection remains, a new verification starts. A transition table makes these cases explicit, including ones a drawing might omit. An enumeration names the set of states in code. Condition order must preserve priority; several independent if statements can conflict if a later branch reactivates what stopping disabled.

The project’s detection must remain present for 1000 ms, or one second, before actuation is allowed. Other inputs still matter during that interval: a stop can arrive while detection is being verified. delay(1000) pauses the continuation of the sequence executing it and can delay a stop checked there. Nonblocking timing meets this need by retaining the starting instant and checking time later while loop continues its reading and decision cycle.

millis() provides a counter in milliseconds. The pattern uses unsigned long times and calculates ahora – inicioDeteccion to determine how much time has elapsed since the start. The >= comparison includes the instant when the interval is reached. The start is stored on entering DETECTADO; updating it on every iteration would restart the count repeatedly. Losing detection before the interval ends, however, does require abandoning that verification: the requirement is continuity rather than adding separate intervals together.

Reaching the interval is only one condition for actuation. Loop iterations also check detection, validity and stop, whose priority is preserved during waiting and actuation. The counter has finite size, so the unsigned subtraction pattern is retained rather than replaced with arbitrary additions. The program also observes the interval only when it checks again. Other instructions can introduce delays, and loop frequency limits that observation; nonblocking timing promises neither instantaneous response nor unlimited precision.

A mechanism relates parts to transmit or guide movement. An idealised barrier rotates around one axis: one independent angular variable describes its position, giving it one degree of freedom in that model. Counting closed, intermediate and open positions does not add degrees of freedom. A mobile base translates and turns on a surface; an articulated arm combines joints; a Cartesian configuration moves along axes. Counting motors does not fully describe mobility.

Selection depends on the task, reach, load, workspace and structure. For the model, an indicator first checks the command without movement. If a servo is added later, check its power, signal, library and permitted travel. A position command alone guarantees neither an exact physical angle nor an unobstructed path. The support must allow movement, return, access and maintenance without forcing stops or cables. Inspect the mechanism with power disconnected before a supervised functional test, keeping parts removable and reusable.

A logic test checks decisions with known inputs; a physical test adds sensor, connections, power and mechanism. Both are necessary and provide different evidence. To investigate a fault, follow reading, interpretation, state, command and physical effect. The first discrepancy guides a hypothesis without proving it yet. A final photograph cannot reconstruct the path or establish whether a message belongs to the current program version.

If the system remains in DETECTADO, it may continually restart timing or receive unstable detection. A stable serial input helps distinguish these before changing the filter. If ACTUANDO appears without movement, inspect output and assembly using the validated sheet; do not randomly alter transitions already working. After repair, repeat the original case and other relevant ones, including stop and recovery. Record version, conditions, expected and observed results, hypothesis and outcome. A sustainable improvement can ease maintenance or reuse but must preserve the verified function of the integrated system.

An acceptance test connects a requirement with an action and an observable result. The controller must disable output at rest, ignore detection shorter than 1000 ms and act when detection continues through the interval. It must also respond to stop or invalidity during actuation and verify again after recovery. Exact temporal equality matters, as does stopping during verification; these are not equivalent to testing only the beginning and end.

The record states whether input comes from the sensor or serial and what diagnostic capability actually exists. Simulated invalidity checks logical priority without establishing physical detection of disconnection. The product combines editable code, connection sheet, mechanism diagram and tests of the integrated assembly. Improvement requires a before-and-after comparison under stated conditions, and each partner must explain a decision and modification. Recognising limitations belongs to the result: the model studies educational control and certifies neither protection of people, mechanical precision nor the safety of a real door.