Make the old board sing again.

02 · Board connections

What every port does.

The three audio jacks are easy to misread: line input and line output are each stereo on one 6.35 mm TRS jack; the smaller jack is a separate stereo headphone output.

03 · Power

USB is easiest. DC is specific.

Use a regulated DC adapter. The board schematic connects the barrel center contact to the protected VIN path and the sleeve to ground. Choose an adapter with enough current for the Core and anything drawing power from its USB host port.

• Never use an AC-output adapter.
• Never use a center-negative supply.
• Never exceed 15 V at the barrel jack.
• Do not inject power into the expansion rails unless you understand the board’s power path.
• When a USB controller causes resets, test without it or use a controller with its own power.

04 · microSD

Small, ordinary, FAT32.

The stock Axoloti 1.0.12-2 firmware uses a FatFs configuration without exFAT. A 64 GB-or-larger SDXC card normally arrives as exFAT and will not work until reformatted; a native FAT32 SDHC card avoids that friction. Speed class is not the bottleneck for this workflow.

For a standalone SoundGraph bank, the card contains:

/start.bin             boots at power-on
/index.axb             lists bank entries
/<patch-name>/patch.bin
/<patch-name>/b0.raw  optional sample or speech data

Program Change 0 selects the first bank entry. Out-of-range program numbers fall back to /start.bin. Power the board off before inserting or removing the card.

05 · Programming

What “program the board” means.

1. 1GraphSave the SoundGraph patch as JSON.
2. 2ResolveSoundGraph expands modules, checks the graph, and fixes execution order.
3. 3Generatesgaxo turns supported nodes into Axoloti C++.
4. 4CompileThe ARM toolchain links a patch binary against stock firmware symbols.
5. 5InstallUpload over micro-USB for development, or copy a baked bank to microSD.
6. 6RunThe firmware starts the binary; the card can boot it without a computer.

Prepare the developer tools

From a SoundGraph source checkout, first build the graph validator. Then prepare the Axoloti SDK and Python environment. The package-install line below is for macOS with Homebrew; use equivalent packages on Linux.

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --target sg-validate

cd embedded/axoloti
brew install libusb arm-none-eabi-gcc arm-none-eabi-binutils
python3 -m venv .venv
.venv/bin/pip install -r requirements.txt
tools/fetch-sdk.sh

Compile one graph

.venv/bin/python sgaxo/codegen.py ../../examples/patches/first-synth.json

The compiled files land in embedded/axoloti/sgaxo/build/. This command proves the patch compiles; the current repository’s hardware-in-the-loop tools perform tethered USB upload and start.

Bake a standalone card

.venv/bin/python tools/bake-bank.py ./card \
  ../../examples/patches/first-synth.json \
  ../../examples/patches/plucked-string.json

Copy the contents of ./card to the root of a blank FAT32 microSD card. A card reader is fastest. Advanced users can add --board to write through a connected Core, but USB card writes are much slower.

Open the current Axoloti backend and test notes ↗

06 · Legacy software

Two patchers, one important firmware choice.

07 · Expansion pinout

The labeled edge pads.

Axoloti names expansion pins by STM32 port: PA0 means MCU port A, pin 0. The board exposes the groups below. Use the labels printed on the PCB and the official schematic for physical placement; this responsive table describes electrical function, not left-to-right pad position.

The board also exposes SWD test points and separate MIDI test points; those are service and hardware-development connections, not ordinary user I/O. See sheet 6 of the schematic for the expansion pads and sheet 7 for MIDI.

Open the Axoloti Core v1.0 schematic ↗

08 · MIDI controllers

Remap by moving the control you mean.

Bind a hardware CC to a face knob

1. Connect the controller before opening SoundGraph. The desktop editor opens the operating system’s MIDI inputs automatically.
2. Open the patch’s Rack view. The target knob must already be exposed on the patch’s Face.
3. Hold Ctrl and click the SoundGraph knob you want to control.
4. When the status message says MIDI Learn is armed, move the desired hardware knob, fader, or pedal.
5. The next MIDI Control Change message replaces that control’s prior binding. Save the patch to keep the mapping.

Press Escape before moving a controller to cancel Learn. Incoming CC values use the SoundGraph control’s own range and scaling, so a logarithmic frequency control still feels logarithmic.

Use a MIDI CC as a graph signal

Add a MIDI CC node when the controller should become a cableable modulation source instead of directly turning a face knob. Press Learn on that node, then move the desired hardware control. The node stores:

CC

The controller number. CC 1 is normally the modulation wheel; set this field to 128 manually when you want pitch bend.

Low / high

The output range produced by MIDI values 0–127.

Resting

The value used before that controller has sent anything.

Glide

Smoothing that removes abrupt steps from knob movement.

09 · Design files

The attached mechanical references.

These files help with enclosure fit, cutting, and CAD. They do not define power requirements or signal pinouts; use the schematic for electrical work.

10 · Troubleshooting

Start with the boring causes.