KarplusStrongMachine – Digital Kalimba on Daisy Seed

A playable Karplus–Strong “digital Kalimba” built on the Daisy Seed platform.
Designed as both an instrument and a teaching tool for exploring physical modelling, microcontrollers, and sound design.

Status: Workshop-ready; evolving with student feedback.

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🎯 What this project is

• A complete hardware + firmware project:
  • Daisy Seed-based audio core
  • Simple controls for tuning, decay, damping, etc.
  • Audio out designed for pedal/synth workflows
• A workshop-ready instrument:
  • Web Flasher so students can program it from a browser (no toolchain needed!)
  • Clear wiring diagrams and parts list
  • Documentation written for people who like to experiment and break things

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🧱 Features

• Karplus–Strong synthesis (plucked string / Kalimba vibe) with 7-voice polyphony
• 5 Selectable Scales (Pentatonic, Dorian, Chromatic, Kalimba, Just Intonation)
• Stereo Reverb (ReverbSc) for spatial depth
• Octave Shift (-2 to +2 range)
• Low Latency (~0.08ms) for responsive playability
• Parameters exposed as simple potentiometers, making it easy to teach DSP concepts like "damping" and "feedback" physically.

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🔌 Hardware Overview

• Core: Electrosmith Daisy Seed (STM32H750)
• Controls:
  • 7 Push Buttons (Notes D1-D7)
  • 6 Potentiometers (Tone, Decay, Octave, Scale, Reverb Mix, Reverb Time)
  • 1 OLED Display (Optional, I2C)
• I/O:
  • Stereo Audio Out (Pins 19/20)
  • USB for flashing

See KALIMBA_WIRING.md for complete wiring details and pinouts.

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🚀 Quickstart

1. The Easy Way (WebUSB)

No coding required. Perfect for workshops.

1. Connect Daisy Seed via USB.
2. Put in bootloader mode (Hold BOOT, press RESET).
3. Go to the Web Flasher.
4. Click "Connect" -> "Flash".

2. The Developer Way (CLI)

For modifying the code and DSP.

git clone https://github.com/willbearfruits/KarplusStrongMachine.git
cd KarplusStrongMachine

# Build
make -j4

# Flash
make program-dfu

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🎓 Teaching & Workshop Use

I use this project in workshops on:

• Synths and Microcontrollers
• Physical Modelling Synthesis
• Building Complete Instruments (DSP + Hardware + Enclosure)

It is intentionally:

• Minimal enough for beginners to follow the signal path.
• Open enough for advanced students to fork (e.g., "change the scale," "add a delay effect," "make it a drone machine").

If you use it in a class, feel free to open an issue or PR with notes!

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🧪 Technical Details

• Platform: Daisy Seed (ARM Cortex-M7 @ 480MHz)
• Audio: 48kHz, 24-bit, 4-sample block size
• DSP: Custom String class (ported from Mutable Instruments Rings)
• CPU Usage: ~15% (plenty of room for more effects)

License

MIT. Break it, bend it, rebuild it.