First, I started by creating an Arduino Timer class that implements a non-blocking countdown timer using the millis() function, allowing the main code to run without interruption. The timer can be started with a duration in minutes, and it automatically adds two extra seconds to the countdown.

A key feature of this class is its ability to pause and resume. When paused, it stops counting by recording the pause time. When resumed, it calculates the elapsed pause duration and extends the final end time accordingly, ensuring the countdown remains accurate.

The class also provides:

• is_finished() → checks if the countdown has ended.

• get_remaining_seconds() → returns the remaining time, freezing the value when paused.

• isSeconds() → a helper function that allows actions (like updating a display) to trigger exactly once per second.

This Arduino code defines a complete PomodoroTimer class, which functions as a self-contained state machine to manage the entire Pomodoro workflow—from work sessions to breaks.

The class uses a modern enum class enState to safely represent its different phases: Idle, Working, Pause, ShortBreak, and LongBreak. This makes the code more reliable and readable compared to using raw values.

At its core, the class encapsulates a separate Timer object to handle countdowns. The main logic is driven by the update() method, which should be called continuously inside the Arduino loop().

When a timer finishes, the private transition_to_next_phase() function is triggered automatically. This acts as the “brain” of the system, deciding whether to start a short or long break based on how many work cycles have been completed.

The class also integrates sound feedback. Private methods such as playSound_WorkStart() use the tone() function to generate unique audio cues for each phase, enhancing the user experience.

Control is simple through public methods like start(), pause(), and resume(). Helper functions such as get_enState() and get_remaining_time() return user-friendly strings for displaying the current status and remaining time on an LCD screen or the Serial Monitor.

Finally, the durations for work and break sessions are defined as constants at the top, making them easy to adjust without changing the core logic. The constructor requires a buzzerPin, ensuring the hardware setup is seamlessly integrated when creating the object.

At the top of the code, several libraries are included to provide essential functionality:

• LiquidCrystal_I2C → for controlling the LCD screen.

• OneButton → for handling advanced button presses such as single, double, and long clicks.

• pomodoro.h → for managing the Pomodoro timer’s logic.

Next, the code defines which Arduino pins are used for the button, buzzer, and ultrasonic distance sensor. After that, the main global objects are created:

• lcd_1 → an object to control the LCD screen.

• pomodoroTimer → the main object that manages the timer’s state, initialized by passing in the buzzerPin.

• button1 → a OneButton object that detects single, double, and long presses.

The setup() Function Explained

The setup() function runs once when the Arduino is powered on or reset. Step by step, it performs the following:

1. Starts Serial Communication

1. • Serial.begin(9600); opens communication with the computer so debug messages can be viewed in the Serial Monitor.

2. Attaches Button Functions

2. • The button1.attach... lines link button actions to specific callback functions.

2. • For example: button1.attachClick(click1); ensures the program runs the click1() function whenever a single click is detected.

3. Initializes the LCD

3. • lcd_1.init(); and lcd_1.backlight(); turn on the display.

3. • setCursor() and clear() prepare the screen for displaying text

4. Starts the Timer

pomodoroTimer.start(); immediately begins the Pomodoro workflow, usually entering the Working state as soon as the device is powered on.

Main loop() Function 🔁

The loop() runs continuously and handles the program’s active tasks:

• Button Monitoring: button1.tick(); checks the button state to detect single, double, or long presses.

• Automatic Pause (Ultrasonic): readUltrasonicInCM() measures distance. If you’re within 100 cm, the timer runs; if farther, it pauses automatically.

• Display Update (Once/Second): pomodoroTimer.get_timer().IsSeconds() ensures the LCD and Serial Monitor update only once per second, preventing flicker and saving resources.

Button & Helper Functions 🖱️

• click1() (Single Click): Toggles pause/resume.

• doubleclick1() (Double Click): Resets the Pomodoro cycle.

• readUltrasonicInCM(): Converts sensor readings into distance (cm).

• longPress...(): Placeholders that currently just print messages to the Serial Monitor.

My peer Ahmed asked me how he could make a timer lock for his phone as part of his final project. I suggested that he could use an LCD with a keypad or push buttons for input. When he asked if he should use an external timer, I recommended using the Arduino’s internal timer since it is easier to implement than an external one. I also told him that he could use a library like OneButton, which simplifies working with push buttons by detecting single, double, long, and even multiple clicks.