Timer
Note
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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 ESP32 board |
PURCHASE LINK |
|---|---|---|
ESP32 Ultimate Starter Kit |
ESP32 WROOM 32E + |
|
Universal Maker Sensor Kit |
Course Introduction
In this lesson, you’ll learn how to create a timer using LED, button, passive buzzer, and I2C LCD 1602 with ESP32.
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 ESP32 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 |
ESP-WROOM-32 ESP32 ESP-32S Development Board |
1 |
|
2 |
USB Type-C cable |
1 |
|
3 |
Breadboard |
1 |
|
4 |
Wires |
Several |
|
5 |
1kΩ resistor |
2 |
|
6 |
Button |
4 |
|
7 |
LED |
2 |
|
8 |
I2C LCD 1602 |
1 |
|
9 |
Passive Buzzer |
1 |
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 GPIO16, GPIO17 on the ESP32.
Button
Connect to breadboard’s negative power bus.
Connect to 32 , 33 , 25 , 26 on the ESP32.
Passive Buzzer
＋: Connect to GPIO27 on the ESP32.
－: Connect to breadboard’s negative power bus.
I2C LCD 1602
SDA: Connect to GPIO21 on the ESP32.
SCL: Connect to GPIO22 on the ESP32.
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(ESP32 Dev module) and the correct port before clicking the Upload button.
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
// ==== I2C LCD ====
LiquidCrystal_I2C lcd(0x27, 16, 2);
// ==== ESP32 pin mapping ====
// Outputs
const int buzzerPin = 27; // Buzzer (active 3.3V, or drive 5V with transistor)
const int led1Pin = 16; // LED1
const int led2Pin = 17; // LED2
// Inputs (buttons with INPUT_PULLUP)
const int buttonRed = 32;
const int buttonYellow = 33;
const int buttonGreen = 26;
const int buttonBlue = 25;
// 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 control
int settingStage = 0;
unsigned long totalSeconds = 0;
// Button state tracking
bool lastYellowState = HIGH;
bool lastGreenState = HIGH;
bool lastBlueState = HIGH;
// Red button debouncing
unsigned long redLastTriggered = 0;
bool redHandled = false;
// Function declarations
void showTitle(String text);
void updateDisplay();
void handleButtons();
void convertTotalSeconds();
void resetTimer();
void handleLEDBlink(int interval);
String formatTime(int val);
void setup() {
Serial.begin(9600);
// Initialize I2C explicitly for ESP32
Wire.begin(21, 22); // SDA=21, SCL=22
lcd.init();
lcd.backlight();
showTitle("Timer");
pinMode(buzzerPin, OUTPUT);
pinMode(led1Pin, OUTPUT);
pinMode(led2Pin, OUTPUT);
pinMode(buttonRed, INPUT_PULLUP);
pinMode(buttonYellow, INPUT_PULLUP);
pinMode(buttonGreen, INPUT_PULLUP);
pinMode(buttonBlue, INPUT_PULLUP);
updateDisplay();
}
void loop() {
handleButtons();
if (state == RUNNING) {
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);
if (millis() - previousMillis >= 3000) {
noTone(buzzerPin);
state = IDLE;
resetTimer();
updateDisplay();
Serial.println("Finished alert done. Returning to IDLE.");
}
}
}
void handleButtons() {
// Red button (start/pause)
bool currentRed = digitalRead(buttonRed);
if (!redHandled && currentRed == LOW && millis() - redLastTriggered > 200) {
redHandled = true;
redLastTriggered = millis();
Serial.println("Red button triggered.");
Serial.print("Current state: "); Serial.println(state);
if (state == READY || state == PAUSED) {
totalSeconds = seconds + minutes * 60 + hours * 3600;
Serial.print("Computed totalSeconds: "); Serial.println(totalSeconds);
if (totalSeconds > 0) {
state = RUNNING;
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;
Serial.println("Switched to PAUSED.");
}
}
if (currentRed == HIGH) redHandled = false;
// Blue button (step through 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() {
String timeStr = formatTime(hours) + " : " + formatTime(minutes) + " : " + formatTime(seconds);
int padding = (16 - timeStr.length()) / 2;
lcd.setCursor(0, 1);
lcd.print(" ");
lcd.setCursor(padding, 1);
lcd.print(timeStr);
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) {
return (val < 10) ? "0" + String(val) : String(val);
}
void convertTotalSeconds() {
hours = totalSeconds / 3600;
minutes = (totalSeconds % 3600) / 60;
seconds = totalSeconds % 60;
}
void resetTimer() {
hours = minutes = seconds = totalSeconds = 0;
digitalWrite(led1Pin, LOW);
digitalWrite(led2Pin, LOW);
noTone(buzzerPin);
settingStage = 0;
Serial.println("Timer reset.");
}
void handleLEDBlink(int interval) {
if (millis() - ledBlinkMillis >= interval) {
ledBlinkMillis = millis();
ledState = !ledState;
digitalWrite(led1Pin, ledState);
digitalWrite(led2Pin, ledState);
}
}
void showTitle(String text) {
lcd.setCursor(0, 0);
lcd.print(" ");
int spaces = (16 - text.length()) / 2;
lcd.setCursor(spaces, 0);
lcd.print(text);
}