Pico DAC Sampler

A RP2040-based eurorack module for sample playback and drum machine functionality. Features multiple voice sample playback, real-time speed/pitch control, and trigger-based sequencing using the Mozzi audio synthesis library.

🎵 Features

Eurorack Module Capabilities

• Multi-voice drum machine with 4 sample slots (kick, snare, hihat, tom)
• Trigger-based sequencing compatible with eurorack trigger signals
• Real-time sample playback using Mozzi audio synthesis library
• I2S audio output via PCM5102A DAC for high-quality audio

Sample Control

• 4-button trigger system with hardware debouncing (GPIO6-9)
• Real-time sample triggering for live performance
• Individual sample assignment per button (Kick, Snare, Hihat, Tom)
• Eurorack-compatible trigger inputs with protection circuitry
• Flash memory storage for embedded drum samples

Hardware Interface

• RP2040 microcontroller optimized for real-time audio
• 0.91" OLED display (128x32) for visual feedback and control
• Eurorack-compatible trigger inputs and CV control
• I2S DAC output (GPIO26=BCK, GPIO27=LCK, GPIO28=DIN)
• I2C interface (GPIO4=SDA, GPIO5=SCL) for OLED display
• Serial interface for development and configuration

🔧 Hardware Requirements

• Raspberry Pi RP2040 microcontroller (Pico or compatible)
• PCM5102A I2S DAC for high-quality audio output
• 0.91" SSD1306 OLED Display (128x32, I2C interface)
• 4x Momentary Push Buttons for sample triggering
• Protection circuitry for eurorack trigger compatibility (optional)
• I2S Connections:
  • GPIO26 → BCK (Bit Clock)
  • GPIO27 → LCK (Word Select) - automatically assigned
  • GPIO28 → DIN (Data Input)
• I2C Connections:
  • GPIO4 → SDA (I2C Data)
  • GPIO5 → SCL (I2C Clock)
• Button Connections:
  • GPIO6 → Button 1 (Kick) → GND
  • GPIO7 → Button 2 (Snare) → GND
  • GPIO8 → Button 3 (Hihat) → GND
  • GPIO9 → Button 4 (Tom) → GND
• Power: 3.3V from eurorack power supply

🎚️ Controls

Serial Commands

Key	Function
SPACE	Trigger sample via serial

Hardware Buttons

Button	GPIO	Function	Sample
Button 1	GPIO6	Trigger Sample 1	Kick Drum
Button 2	GPIO7	Trigger Sample 2	Snare Drum
Button 3	GPIO8	Trigger Sample 3	Hi-hat
Button 4	GPIO9	Trigger Sample 4	Tom

Hardware buttons work in both sine wave and sample modes

🚀 Getting Started

Prerequisites

• PlatformIO installed
• RP2040 development board
• I2S DAC/amplifier module

Installation

1. Clone this repository:

   git clone https://github.com/funkfinger/pico-dac-sampler.git
   cd pico-dac-sampler

2. Build and upload:

   pio run --target upload

3. Open serial monitor:

   pio device monitor --baud 115200

Adding Your Own Audio

1. Place your WAV file in the source/ directory
2. Run the conversion script:

   python3 convert_wav.py

3. Include the generated header file in main.cpp

📊 Technical Specifications

• Memory Usage: 9.2% RAM, 13.7% Flash
• Audio Quality: Linear interpolation with fractional positioning
• Buffer Size: 512 samples for smooth playback
• Sample Rate: 16kHz (automatically converted from source)
• Bit Depth: 16-bit signed integers
• Channels: Mono (stereo automatically mixed to mono)

🎯 Creative Applications

LINKED Mode (Speed + Pitch together)

• 0.5x: Classic slow-motion with lower pitch
• 2.0x: Fast playback with higher pitch (chipmunk effect)

INDEPENDENT Mode (Separate controls)

• Speed 0.5x, Pitch 1.0x: Slow motion with normal pitch
• Speed 1.0x, Pitch 1.5x: Normal speed with higher pitch
• Speed 2.0x, Pitch 0.8x: Fast playback with lower pitch

📁 Project Structure

├── src/
│   ├── main.cpp              # 4-button drum machine with sample playback
│   ├── step_sample.h         # Embedded audio sample data
│   └── main_mozzi.cpp        # Backup reference file
├── source/                   # Original drum samples (to be added)
├── AI/
│   └── user_stories.md       # Project roadmap and user stories
├── convert_wav.py           # WAV to Mozzi format converter (to be updated)
└── platformio.ini           # Project configuration with Mozzi

🛠️ Development

The project uses the Mozzi audio synthesis library for efficient real-time audio generation and the arduino-pico core for RP2040 support.

Current Implementation

• updateAudio(): Mozzi audio generation callback (16kHz) for sample playback
• updateControl(): Mozzi control callback (64Hz) for button processing
• audioOutput(): Custom I2S output function for external DAC
• updateButtons(): Hardware debouncing and trigger detection
• processButtonTriggers(): Sample triggering logic

Planned Features

• Multi-voice sample playback engine
• Trigger input handling for eurorack compatibility
• Real-time speed/pitch control per voice
• CV input processing for parameter modulation

📄 License

This project is open source. Feel free to use, modify, and distribute.

🤝 Contributing

Contributions are welcome! Please feel free to submit issues, feature requests, or pull requests.

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Built with ❤️ for the eurorack and RP2040 communities