The Pico MIDI Looper is a minimalist 2-bar drum looping device that leverages the Raspberry Pi Pico's capabilities to provide MIDI functionality via USB (USB-MIDI) and, on Pico W hardware, via BLE (BLE-MIDI). Its primary purpose is to offer a compact, easy-to-build musical instrument that enables rhythm creation with minimal hardware requirements.
The system is designed for:
- Educational contexts and workshops
- Live performance setups
- Prototyping musical ideas
- Minimalist music creation
The looper requires only the standard Raspberry Pi Pico hardware with no additional components, utilizing just the onboard BOOTSEL button for all interactions.
| Feature | Description |
|---|---|
| USB-MIDI Compatibility | Connects directly to DAWs and synth apps via USB |
| BLE-MIDI Compatibility | Connects wirelessly to DAWs and synth apps via Bluetooth LE |
| 2-Bar Pattern Length | 32 steps (4 beats × 4 subdivisions × 2 bars) |
| 4-Track Structure | Separate tracks for different drum sounds |
| Tap-Tempo | Set BPM by tapping the button |
| Quantized Input | Notes automatically align to 16th-note grid |
| LED Feedback | Visual indication of current step |
| Serial Display | Pattern visualization via terminal |
| Single-Button Control | All functions accessible through one button |
The system is intentionally minimalist yet expressive, providing musicians with a compact but capable looping tool.
Note: The prebuilt
.uf2available on the Releases page is compiled for the non-wireless Pico board and does not include BLE-MIDI support. To enable BLE-MIDI on a Pico W, please build from source with CYW43 enabled.
You can either download a prebuilt .uf2 from the Releases page, or build it yourself.
To flash the firmware:
- Hold the
BOOTSELbutton while connecting your Raspberry Pi Pico via USB. - Copy the
pico-midi-looper.uf2file onto the mounted USB drive. - The device will reboot and start running the looper.
- Open a USB-MIDI compatible app (e.g., GarageBand on iOS).
- Start recording and playing right away.
For detailed instructions on iOS, see Getting Started with GarageBand
You build up your loop by switching between four tracks and entering notes step by step. Once powered on, the looper is ready to use. All interaction is handled via a single button. The length of your press determines the action.
Interaction with the Pico MIDI Looper is handled entirely through the single BOOTSEL button, with different press durations triggering different functions.
| Action | Duration | Function |
|---|---|---|
| Click | < 0.5s | Record a note on the current track |
| Press | ≥ 0.5s | Switch to the next track |
| Long Press | ≥ 2s | Enter tap-tempo mode |
| Very Long Press | ≥ 5s | Clear all tracks |
The button interface is handled by a dedicated subsystem that detects press durations and generates appropriate events.
The looper provides four distinct tracks, each associated with a specific MIDI note number that corresponds to standard General MIDI drum sounds:
| Track | Sound | MIDI Note |
|---|---|---|
| Track 1 | Bass Drum | 36 |
| Track 2 | Snare Drum | 38 |
| Track 3 | Closed Hi-Hat | 42 |
| Track 4 | Open Hi-Hat | 46 |
Additionally, the system uses two special sounds for feedback:
- Hand Clap (MIDI Note 39) for track switching cues
- Rim Shot (MIDI Note 37) for metronome clicks
These MIDI notes are defined in the code and transmitted to compatible receivers via USB-MIDI and/or BLE-MIDI.
When connected to a USB serial terminal, the Pico MIDI Looper provides a visual representation of the current patterns across all tracks:
The display shows:
- All four tracks labeled by their drum sound
- A 32-step sixteenth-note loop (2 bars)
- The current playback position
This visual feedback makes it easier to understand the current pattern and position during playback and recording.
This project uses the pico-sdk. Refer to the official guide, Getting Started with Raspberry Pi Pico, to set up your development environment.
Once ready:
git clone https://github.com/oyama/pico-midi-looper.git
cd pico-midi-looper
mkdir build && cd build
PICO_SDK_PATH=/path/to/pico-sdk cmake ..
makeThis will produce pico‑midi‑looper.uf2 in the build directory.
The firmware follows a clear two‑layer design.
Located under src/, the core consists of fewer than three hundred lines of hardware‑agnostic C. It is orchestrated by one main finite‑state machine—the looper, which advances the step sequencer—and one subsidiary FSM: the tap‑tempo estimator, which transforms a series of taps into a BPM value.
+Residing in drivers/, the drivers provide the project’s only connection to hardware. Each driver exposes a narrow C interface and fulfils a single purpose— for example, sending MIDI packets over USB (USB-MIDI) or Bluetooth LE (BLE-MIDI), debouncing the BOOTSEL switch, or printing a visualisation over UART. Replacing a driver (e.g. switching from a UART text view to an OLED display) requires no changes to the core and no rebuild of the remaining drivers.
At run time the three state machines advance in response to two independent streams of events:
- Tempo ticks – A timer fires at an interval derived from the current BPM. Each tick calls
looper_handle_tick, moving the sequencer forward by exactly one step with sample‑accurate timing. - Button events – The button driver debounces the hardware switch and raises high‑level events such as
CLICK_RELEASEorHOLD_RELEASE. These events are processed bylooper_handle_input, enabling the user to start or stop recording, switch tracks, clear patterns, or enter tap‑tempo mode.
This split keeps time‑critical audio pacing deterministic while preserving a responsive user interface.
Read the full design in docs/architecture.md.
This project is licensed under the 3-Clause BSD License. For details, see the LICENSE file.
Simplicity is at the heart of this project. We welcome pull requests and issues that help refine the code or enhance the user experience — while keeping things minimal and readable. Feel free to fork the project and adapt it to your own creative or educational needs. We’d love to see how you build upon this tiny MIDI machine.
Made with love in Japan.