Pocket Metronome

Pocket Metronome is a visual and audible metronome for the M5StickC Plus2. It uses the built-in display, buttons, and passive buzzer, so no additional hardware is required.

The firmware provides:

• adjustable tempo from 30 to 300 BPM;
• a four-beat visual pulse with a distinct downbeat;
• separate accent and regular click sounds;
• adjustable buzzer volume;
• immediate playback from startup;
• phase-preserving tempo changes;
• suppression of stale clicks when the event loop is delayed.

Controls

The firmware opens on the BPM screen. Short-click the Power button to cycle through BPM, Volume, and Sounds, then return to BPM.

Screen	Button A	Button B	Power click
BPM	+1 BPM	-1 BPM	Volume
Volume	Louder	Quieter	Sounds
Sounds	Next accent	Next regular click	BPM

The footer always shows the current A/B actions followed by the destination of the next Power click. A long Power hold retains the device's normal power behavior.

Build and flash

The project uses PlatformIO with the Arduino framework and pioarduino's stable ESP32 platform.

just build
just upload
just monitor

just upload-monitor flashes the firmware and opens the serial monitor. just devices lists available serial devices, and just clean removes the local PlatformIO build output.

The application resolves its reusable components from the PlatformIO Registry:

• fcz2/m5-tone-output@0.1.5;
• fcz2/step-trigger@0.2.0;
• their published monophonic-instrument, musical-clock, and firmware-contracts dependencies.

It does not require sibling repository checkouts.

Architecture

The metronome represents one bar as a four-step TriggerPattern: a strong first step followed by three normal steps. TriggerPatternPlayer owns the pattern cursor and its AlternatingDeadlineClock, advances from monotonic microsecond timestamps, and emits trigger events for audible beats.

The application remains responsible for translating that shared playback machinery into a metronome:

• ControlSurface maps short Power clicks and A/B releases to commands;
• MetronomeState owns tempo, volume, screen mode, and sound selections;
• MetronomeDisplay draws controls and the four-beat pulse;
• MetronomeAudio owns the passive-buzzer output and keep-alive policy;
• MetronomeClickSamples builds the selectable PCM click catalog;
• main.cpp composes the pattern source, player, trigger sink, UI, and audio.

Tempo changes preserve the fraction of the current beat interval that remains. If polling arrives late, musical position catches up but missed clicks are not replayed as an audio burst.

M5Burner package

VERSION is the firmware release version. Generate the merged full-flash image and checksum with:

just package-m5burner

The artifacts are written under dist/m5burner/. The .bin contains the bootloader, partition table, Arduino boot metadata, and application and is intended to be flashed at address 0x0.

See the M5Burner publishing guide for the hardware release gate, upload steps, and suggested directory metadata.

Development history

The project is developed in small, hardware-testable slices. Narrative records of the timing experiments, audio probes, shared-package extractions, UI decisions, and release work live in docs/devlog.

Possible future slices include selectable meter and click grouping, transport controls, and persisted tempo, volume, and sound choices.