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Aarebot

Dynamic realtime stereo sampler for Eurorack modular synthesizer - STM32H7

Aarebot is a dynamic realtime sampler built as a Eurorack module. At its core is a stereo tape-style engine with a hot-swapping record/playback buffer - this enables to record and play simultaneously. Slicing markers can be added on the fly, and processing through an onboard effects chain.

Samplerate decimation trades fidelity for buffer length. A Schroeder reverb implementation reaching from spacious room to sharp metallic resonance ringing depending on the XY effect mapping.

More DSP FX and taillred XY mapping is on the way and will turn Aarebot into an IDM LOFI crunch machine.

Features

Audio Engine

  • Stereo hot-swap record/playback buffer
  • Realtime sample slicing with manual slice marker placement
  • Hermite interpolation for smooth pitch shifting (±24 semitones)
  • V/Oct pitch tracking (−1.5 V to +5 V)
  • Samplerate decimation for extended recording time and lo-fi texture
  • Nonlinear exciter
  • Schroeder reverb with prime-length delay lines and scalable room size

Control

Interface Function
Pot 1 Base pitch (±24 semitones)
Pot 2 Envelope attack
Pot 3 Envelope decay / release
Pot 4 Recording decimation
V/Oct Pitch CV input
CV 2 XY effect plane - X axis
CV 3 XY effect plane - Y axis
Gate 1 Record
Gate 2 Play
Gate 3 (unassigned)
Gate 4 Set slice marker

Hardware

  • STM32H7 MCU
  • Custom I2C audio codec driver
  • 4x WS2812 RGB LEDs for visual feedback
  • ADC calibration with 2-point and piecewise CV calibration
  • Full KiCad schematic and PCB design
  • SPICE simulations for analog input/output stages

Repository Structure

├── firmware/                 STM32CubeMX project and C source
|   ├── Aware                 Main firmware implementation
|   └── Src                   CubeMX generated src files
├── hardware/
│   ├── aware01_h7_rev2_0/    KiCad schematic and PCB
│   └── simulation/           SPICE simulations for analog stages
└── docs/
    ├── images/               PCB renders and oscilloscope captures
    ├── ba/                   Bachelor thesis
    │   ├── latex/            LaTeX source files
    │   ├── images/           Figures and plots
    │   ├── diagrams/         DrawIO block diagrams
    │   └── scripts/          Python scripts for analysis and plots
    └── project_management/   Project planning documents
        ├── lastenheft.tex    Requirements specification
        ├── pflichtenheft.tex Functional specification
        └── projectplan.tex   Project plan

Building

Dependencies

Tool Arch Debian/Ubuntu
ARM cross-compiler arm-none-eabi-gcc gcc-arm-none-eabi
ARM newlib arm-none-eabi-newlib libnewlib-arm-none-eabi
CMake ≥ 3.22 cmake cmake
Ninja ninja ninja-build

Compile

cd firmware

# Configure + build (Debug)
cmake --preset Debug
cmake --build --preset Debug

# Configure + build (Release)
cmake --preset Release
cmake --build --preset Release

The output ELF is at firmware/build/Debug/firmware.elf.

Flash

Requires an ST-Link probe. Either st-flash (stlink) or openocd can be used.

openocd (recommended; works directly with ELF):

openocd -f interface/stlink.cfg -f target/stm32h7x.cfg \
  -c "program firmware/build/Debug/firmware.elf verify reset exit"

st-flash (requires converting ELF to binary first):

arm-none-eabi-objcopy -O binary \
  firmware/build/Debug/firmware.elf \
  firmware/build/Debug/firmware.bin

st-flash write firmware/build/Debug/firmware.bin 0x8000000
Tool Arch Debian/Ubuntu
openocd openocd openocd
st-flash stlink stlink-tools

Hardware

Designed in KiCad. The hardware directory contains the full schematic, PCB layout, and SPICE simulations for the analog input and output conditioning stages.

KiCad Library

Opening the KiCad project requires the custom component library. Clone it alongside this repo:

git clone https://github.com/95lux/kicad_library

Then add it as a global library in KiCad: Preferences → Manage Symbol Libraries (and Manage Footprint Libraries), pointing to the cloned directory.

Specifications

Audio

Parameter Value
Sample rate 48 kHz
Bit depth 16-bit
Recording buffer 2.5 s (stereo)
End-to-end latency ~1.9 ms
Audio codec TLV320AIC3204

Hardware

Parameter Value
MCU STM32H7A3RITx (Cortex-M7, 280 MHz)
Form factor 10 HP, 3U Eurorack
Audio I/O levels ±5 V
CV input range ±10 V
V/Oct range −1.5 V to +5 V
Power (+12V) ~80 mA idle, ~140 mA peak
Power (−12V) ~20 mA

License

Component License
Firmware / software GPL-3.0
Hardware (schematics, PCB, SPICE) CERN OHL-S v2
Thesis / documentation CC BY 4.0