Timer

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Kit purchase

Looking for parts? Check out our all-in-one kits below — packed with components, beginner-friendly guides, and tons of fun.

Name	Includes Arduino board	PURCHASE LINK
Elite Explorer Kit	Arduino Uno R4 WiFi	BUY
3 in 1 Ultimate Starter Kit	Arduino Uno R4 Minima	BUY

Course Introduction

In this lesson, you’ll learn how to create a timer using LED, button, passive buzzer, and I2C LCD 1602 with Arduino.

After setting the countdown by pressing the button, the LED will blink every second, and when the countdown ends, the buzzer will sound, and the LED will keep flashing.

Note

If this is your first time working with an Arduino project, we recommend downloading and reviewing the basic materials first.

Required Components

In this project, we need the following components:

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Arduino UNO R4 Minima	1	BUY
2	USB Type-C cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	1kΩ resistor	2	BUY
6	Button	4	BUY
7	LED	2	BUY
8	I2C LCD 1602	1	BUY
9	Passive Buzzer	1	BUY

Wiring

Common Connections:

LED
- Connect the LEDs cathode to a 1kΩ resistor then to the negative power bus on the breadboard, and the LEDs anode to 4, 5 on the Arduino.
Button
- Connect to breadboard’s negative power bus.
- Connect to 8 to 11 on the Arduino.
Passive Buzzer
- ＋: Connect to 2 on the Arduino.
- －: Connect to breadboard’s negative power bus.
I2C LCD 1602
- SDA: Connect to A4 on the Arduino.
- SCL: Connect to A5 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.

Writing the Code

Note

You can copy this code into Arduino IDE.
To install the library, use the Arduino Library Manager and search for LiquidCrystal I2C and install it.
Don’t forget to select the board(Arduino UNO R4 Minima) and the correct port before clicking the Upload button.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);

// Pin definitions
const int buzzerPin = 2;
const int led1Pin = 4;
const int led2Pin = 5;
const int buttonRed = 8;
const int buttonYellow = 9;
const int buttonGreen = 10;
const int buttonBlue = 11;

// Timer states
enum TimerState { IDLE, SET_SS, SET_MM, SET_HH, READY, RUNNING, PAUSED, FINISHED };
TimerState state = IDLE;

// Time variables
int seconds = 0, minutes = 0, hours = 0;
unsigned long previousMillis = 0;
unsigned long ledBlinkMillis = 0;
bool ledState = false;

// Setting process control
int settingStage = 0;
unsigned long totalSeconds = 0;

// Button state tracking
bool lastYellowState = HIGH;
bool lastGreenState = HIGH;
bool lastBlueState = HIGH;

// Variables for enhanced red button handling
unsigned long redLastTriggered = 0;
bool redHandled = false;

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  showTitle("Timer");

  pinMode(buzzerPin, OUTPUT);
  pinMode(led1Pin, OUTPUT);
  pinMode(led2Pin, OUTPUT);

  // Use internal pull-up resistor for buttons
  pinMode(buttonRed, INPUT_PULLUP);
  pinMode(buttonYellow, INPUT_PULLUP);
  pinMode(buttonGreen, INPUT_PULLUP);
  pinMode(buttonBlue, INPUT_PULLUP);

  updateDisplay();
}

void loop() {
  handleButtons();

  if (state == RUNNING) {
    // Update timer every second
    if (millis() - previousMillis >= 1000) {
      previousMillis = millis();
      Serial.print("Tick: ");
      Serial.println(totalSeconds);
      if (totalSeconds > 0) {
        totalSeconds--;
        convertTotalSeconds();
        updateDisplay();
      } else {
        state = FINISHED;
        showTitle("Time's up!");
        tone(buzzerPin, 1000);
        previousMillis = millis();
        Serial.println("Countdown finished. Entered FINISHED state.");
      }
    }
    handleLEDBlink(500);
  } else if (state == FINISHED) {
    handleLEDBlink(200);
    // After 3 seconds, stop alarm and reset
    if (millis() - previousMillis >= 3000) {
      noTone(buzzerPin);
      state = IDLE;
      resetTimer();
      updateDisplay();
      Serial.println("Finished alert done. Returning to IDLE.");
    }
  }
}

void handleButtons() {
  // Enhanced red button with debouncing
  bool currentRed = digitalRead(buttonRed);
  if (!redHandled && currentRed == LOW && millis() - redLastTriggered > 200) {
    redHandled = true;              // Mark this press as handled
    redLastTriggered = millis();    // Update last trigger time
    Serial.println("Red button triggered.");
    Serial.print("Current state: "); Serial.println(state);

    if (state == READY || state == PAUSED) {
      // Calculate total time in seconds from hours, minutes, and seconds
      totalSeconds = seconds + minutes * 60 + hours * 3600;
      Serial.print("Computed totalSeconds: "); Serial.println(totalSeconds);
      if (totalSeconds > 0) {
        state = RUNNING;            // Start countdown
        previousMillis = millis();
        Serial.println("Switched to RUNNING.");
      } else {
        showTitle("Time = 0!");
        Serial.println("Time is 0. Cannot start.");
        for (int i = 0; i < 4; i++) {
          tone(buzzerPin, 2000);
          digitalWrite(led1Pin, HIGH);
          digitalWrite(led2Pin, HIGH);
          delay(100);
          noTone(buzzerPin);
          digitalWrite(led1Pin, LOW);
          digitalWrite(led2Pin, LOW);
          delay(100);
        }
      }
    } else if (state == RUNNING) {
      state = PAUSED;              // Pause the countdown if running
      Serial.println("Switched to PAUSED.");
    }
  }
  if (currentRed == HIGH) redHandled = false;

  // Blue button: step through time setting stages
  bool currentBlue = digitalRead(buttonBlue);
  if (lastBlueState == LOW && currentBlue == HIGH) {
    Serial.println("Blue button released.");
    if (state == IDLE || state == SET_SS || state == SET_MM || state == SET_HH || state == READY) {
      settingStage++;
      Serial.print("Setting stage: "); Serial.println(settingStage);
      if (settingStage == 1) state = SET_SS;
      else if (settingStage == 2) state = SET_MM;
      else if (settingStage == 3) state = SET_HH;
      else {
        totalSeconds = seconds + minutes * 60 + hours * 3600;
        state = READY;
        settingStage = 0;
        Serial.print("Time set to: "); Serial.println(totalSeconds);
        Serial.println("Entered READY state.");
      }
      updateDisplay();
    }
  }
  lastBlueState = currentBlue;

  // Green button: increase time value
  bool currentGreen = digitalRead(buttonGreen);
  if (lastGreenState == LOW && currentGreen == HIGH) {
    Serial.println("Green button released.");
    if (state == SET_SS) {
      seconds = (seconds + 1) % 60;
      Serial.print("Seconds set to: "); Serial.println(seconds);
    } else if (state == SET_MM) {
      minutes = (minutes + 1) % 60;
      Serial.print("Minutes set to: "); Serial.println(minutes);
    } else if (state == SET_HH) {
      hours = (hours + 1) % 100;
      Serial.print("Hours set to: "); Serial.println(hours);
    }
    updateDisplay();
  }
  lastGreenState = currentGreen;

  // Yellow button: reset timer
  bool currentYellow = digitalRead(buttonYellow);
  if (lastYellowState == LOW && currentYellow == HIGH) {
    Serial.println("Yellow button released. Resetting timer.");
    state = IDLE;
    resetTimer();
    updateDisplay();
  }
  lastYellowState = currentYellow;
}

void updateDisplay() {
  // Format and center the time string on the LCD
  String timeStr = formatTime(hours) + " : " + formatTime(minutes) + " : " + formatTime(seconds);
  int padding = (16 - timeStr.length()) / 2;
  lcd.setCursor(0, 1);
  lcd.print("                "); // Clear second line
  lcd.setCursor(padding, 1);
  lcd.print(timeStr);

  // Set title text based on current state
  if (state == SET_SS) showTitle("Set Timer SS");
  else if (state == SET_MM) showTitle("Set Timer MM");
  else if (state == SET_HH) showTitle("Set Timer HH");
  else if (state == READY || state == PAUSED || state == RUNNING) showTitle("Timer");
  else if (state == IDLE) showTitle("Timer");
}

String formatTime(int val) {
  // Convert time value to two-digit string
  return (val < 10) ? "0" + String(val) : String(val);
}

void convertTotalSeconds() {
  // Convert totalSeconds into hours, minutes, and seconds
  hours = totalSeconds / 3600;
  minutes = (totalSeconds % 3600) / 60;
  seconds = totalSeconds % 60;
}

void resetTimer() {
  // Reset all time values and outputs
  hours = minutes = seconds = totalSeconds = 0;
  digitalWrite(led1Pin, LOW);
  digitalWrite(led2Pin, LOW);
  noTone(buzzerPin);
  settingStage = 0;
  Serial.println("Timer reset.");
}

void handleLEDBlink(int interval) {
  // Blink LEDs at the given interval
  if (millis() - ledBlinkMillis >= interval) {
    ledBlinkMillis = millis();
    ledState = !ledState;
    digitalWrite(led1Pin, ledState);
    digitalWrite(led2Pin, ledState);
  }
}

void showTitle(String text) {
  // Clear the title line and display centered text
  lcd.setCursor(0, 0);
  lcd.print("                "); // Clear first line
  int spaces = (16 - text.length()) / 2;
  lcd.setCursor(spaces, 0);
  lcd.print(text);
}