ComposerMIDICV

Composer MIDICV

A four-channel MIDI-to-CV/Gate Eurorack module, built around the RP2354A.

Composer connects a DAW or MIDI instrument to analog synthesizers through USB MIDI or a 3.5 mm TRS MIDI input. Four CV outputs and four Gate outputs provide pitch, velocity, modulation, random voltages and clock signals across six hardware-selected modes.

USER_MANUAL · Firmware guide · ManufacturingGuide

Features

• USB MIDI input and TRS MIDI input
• Four unipolar CV outputs, with a firmware range of 0–8 V
• Four nominal 0/5 V Gate outputs
• Mono, dual-voice and four-voice MIDI modes, plus three dual-voice clock/transport modes.
• RGB note feedback, out-of-range indication and mode-change feedback.

Specifications

Modes

Modes are selected by the two panel switches, not by changing the MIDI channel. MIDI channels select voices within the active mode.

In the dual-voice modes, MIDI channels 1–8 control Voice 1 and 9–16 control Voice 2. In midi3, the channel groups are 1–4, 5–8, 9–12 and 13–16. Each group controls one voice; playing a chord on a single channel does not automatically distribute it across four outputs.

Pitch conversion uses MIDI note 36 = 0 V, with one octave per volt and a fixed pitch-bend range of approximately ±2 semitones. Velocity and CC1 map linearly from 0–127 to 0–8 V. The manual includes complete routing tables and patch examples.

Quick start

1. With the rack powered off, connect the module's 10-pin power header in the correct orientation. v1.0 uses the rack's +12 V rail; USB-C provides the data connection and does not replace the module power supply.
2. Power the module and connect USB-C to a computer using a data cable, or connect a MIDI source to the TRS Type A input.
3. Select midi1. In your DAW, choose Composer MIDICV / MIDICV MIDI as the MIDI output destination; the exact displayed name depends on the host.
4. Patch CV1 to a VCO's 1 V/oct input and Gate1 to an envelope gate input. Send notes on MIDI channel 1, starting at note 36 or higher.
5. For modes 4–6, enable MIDI Clock and Start/Continue/Stop output to the module as well as MIDI notes.

See the user manual for power pin assignments, the mode selector, dual/four-voice patches, clock routing, flashing, calibration and troubleshooting.

Design

The firmware is written in C, using Raspberry Pi Pico SDK 2.2.0 and TinyUSB. USB packets and the UART MIDI stream are decoded into a common event format, then dispatched to the selected mode. The mode engine updates a shared output state; a 1 ms service loop handles switches, triggers, LEDs and output updates.

Two MCP4822 dual-channel 12-bit DACs provide four CV channels through SPI frames generated by GPIO. An OPA4991 analog stage scales the DAC outputs, while a 74AHCT244 buffer drives the DAC interface and Gate signals. The TRS input uses a TLP2361 optocoupler. The mainboard and front panel are maintained as KiCad 10 projects.

The firmware separates hardware drivers, MIDI parsing/routing, musical modes, pitch/calibration and UI feedback. The six default modes are defined in mode_config.c.

Build and flash

Install CMake 3.22+, Ninja, Python 3 and an Arm GNU embedded toolchain with newlib and nosys.specs. The local build uses Arm GNU 14.2.Rel1. Put arm-none-eabi-gcc and the accompanying tools on PATH.

From the project root, initialize the SDK dependency:

git submodule update --init --recursive third_party/pico-sdk

macOS / Linux:

export PICO_SDK_PATH="$PWD/third_party/pico-sdk"
cmake -S firmware -B firmware/build-arm -G Ninja \
  -DPICO_PLATFORM=rp2350-arm-s -DPICO_BOARD=pico2 \
  -DCMAKE_BUILD_TYPE=Release
cmake --build firmware/build-arm --parallel

Windows PowerShell:

$env:PICO_SDK_PATH = Join-Path $PWD "third_party/pico-sdk"
cmake -S firmware -B firmware/build-arm -G Ninja -DPICO_PLATFORM=rp2350-arm-s -DPICO_BOARD=pico2 -DCMAKE_BUILD_TYPE=Release
cmake --build firmware/build-arm --parallel

The build produces firmware/build-arm/composer_midicv.uf2 and copies it to firmware/dist/composer_midicv.uf2. pico2 supplies the SDK build configuration for the custom RP2354A board; the module's pin mapping is defined in the firmware.

With module power available, enter USB boot mode by holding BOOTSEL while resetting the board with RUN. Connect USB and copy the UF2 to the mounted RP2350 boot drive, then allow the board to reboot. See the flashing instructions for the full sequence.

Hardware and manufacturing files

Use the v1.0 mainboard files together with the current panel files:

Use the v1.0 production BOM linked above for the current revision. Some BOM entries require separate sourcing, including the jacks and RP2354A; the L3 supplier field contains a manufacturer part number rather than an LCSC C... identifier.

The symbols and custom footprints used in v1.0 are included as project-local snapshots. Install the standard KiCad 10 libraries; optional 3D models still use external library variables. See the manufacturing guide for file selection and library details.

License

The author's original source and design files use AGPL-3.0-only; see LICENSE. Third-party material retains its own licence; see THIRD_PARTY_NOTICES.md.

Contact

Email: tg3299182383@gmail.com