ESP32 Digital Alarm Clock

A digital alarm clock running on an ESP32 microcontroller, built as a coursework project for the Microprocessor and Embedded Systems course at FIT VUT. The whole thing - timekeeping, alarm logic, display rendering, and encoder input - is implemented from scratch in C++ on top of the Arduino framework, using PlatformIO as the build system.

Demo

Video, featuring a Slovak voiceover, showcasing the physical build and all functionality.

What it does

• Keeps time in software and shows it on a 128x64 SSD1306 OLED over SPI
• Fully configurable alarm - set the time, pick one of 3 melodies (Fast Beep, Slow Pulse, SOS Rhythm), enable/disable it, and configure how many times it retries if you snooze
• Snooze with a click, dismiss with a long-press while the alarm is firing
• Live melody preview when browsing through alarm sounds
• Everything navigated with a single rotary encoder - rotate to scroll, click to confirm, long-press to go back

Hardware

The project uses an ESP32 D1 R32 board. Here's how everything is wired up:

Component	GPIO
OLED SSD1306 (SPI) - SCLK	18
OLED SSD1306 (SPI) - MOSI	23
OLED SSD1306 (SPI) - CS	5
OLED SSD1306 (SPI) - DC	27
OLED SSD1306 (SPI) - RST	17
Rotary encoder - CLK	16
Rotary encoder - DT	14
Rotary encoder - SW	19
Buzzer	26
LED	25

Code structure

Each piece of hardware has its own module, and the UI lives separately in main.cpp as a simple state machine:

Module	What it handles
TimeManager	Software clock, tick() on every loop iteration, second tracking
AlarmManager	All alarm logic, triggering, snooze, retries, melody selection
Display	Every screen: home clock view, menus, and all the edit screens
Encoder	Debounced rotary encoder with a small event queue and long-press
Buzzer	Plays timed on/off patterns on the buzzer pin
LED	Same pattern system as the buzzer, for visual feedback
main.cpp	The UI state machine that ties everything together

The navigation flow looks like this:

Home
  -> Menu
    -> EditTime
    -> EditAlarmTime
    -> EditEnabled
    -> EditMelody
    -> EditAttempts
    -> EditInterval

Long-press anywhere in the menus goes back. While the alarm is ringing, click snoozes and long-press stops it for good.

UI screenshots

The whole interface is driven by a single rotary encoder. Rotate to move through a menu or change a value, click to confirm or advance to the next field, and long-press to cancel and go back. Every edit screen shows [L: CANCEL] and [C: SAVE] or [C: NEXT] at the bottom so you never have to guess.

Home screen	Main menu
Current time up top, alarm time, retry config, and current state below	Rotate to scroll through settings, click to go in

Set time	Set alarm time
Hours, minutes, and seconds edited one field at a time; active field is underlined	Same as set time, but just hours and minutes

Alarm enable	Melody selection
One encoder turn to flip between ON and OFF, then click to save	The buzzer and LED preview the melody live as you scroll

Retry attempts	Retry interval
How many times the alarm fires again after a snooze before giving up	How many seconds to wait between retries

Building and flashing

You'll need PlatformIO - either the CLI or the VS Code extension works fine.

pio run                  # build
pio run --target upload  # flash
pio device monitor       # serial monitor at 115200 baud

Library dependencies (Adafruit GFX and Adafruit SSD1306 >= 2.5.15) are declared in platformio.ini and fetched automatically.

Files

esp32_budik/
  platformio.ini           # build config & dependencies
  src/
    main.cpp             # UI state machine & entry point
    AlarmManager.{h,cpp} # alarm logic
    Buzzer.{h,cpp}       # buzzer driver
    Display.{h,cpp}      # OLED rendering
    Encoder.{h,cpp}      # rotary encoder driver
    LED.{h,cpp}          # LED driver
    TimeManager.{h,cpp}  # software clock
  doc/
    doc.tex              # project documentation (LaTeX)