Xva1-ui

XVA1 User Interface

A hardware user interface for the XVA1 virtual analog synthesizer, inspired by the Hydrasynth's layout. The XVA1 (and its FM sibling the XFM2) is built on an Artix-7 FPGA but has no built-in UI — this project adds one.

Overview

The UI board provides:

• 1 main rotary encoder — patch selection and menu navigation
• 8 parameter rotary encoders — control up to 8 synth parameters at once
• 4 OLED displays (128×64) — show parameter names and values for each encoder pair
• 1 TFT display (240×240) — main display showing patch name, section, and subsection
• 8 shortcut buttons with LEDs — jump directly to parameter sections (Oscillators, Filters, Envelopes, LFOs, etc.). Hold SHIFT + buttons 1–4 to access sections 9–12
• Up/Down buttons with LEDs — scroll through parameter pages within a section

The design goal was minimal menu-diving: select a section with one button press, then tweak up to eight parameters directly with the encoders.

Hardware

• MCU: Seeed XIAO ESP32-S3 (240 MHz, dual-core)
• IO expansion: 2× MCP23017 (the 8 parameter encoders connect via I2C)
• Display mux: TCA9548A I2C multiplexer for the 4 OLED displays
• Synth connection: UART at 500,000 baud (D6 TX, D7 RX)
• PCB size: 285 mm × 130 mm
• Buttons: PB86-B1 (with LED) / PB86-B0 (without LED), available from AliExpress

KiCad schematics are in the Hardware/ directory.

Build History

The project started in early 2021 on a breadboard with a Seeeduino XIAO (SAMD21), then moved to an ESP32 devboard when memory became a bottleneck, and eventually settled on the Seeed XIAO ESP32-S3 as a drop-in replacement with the same footprint. The first PCB prototype was ordered from JLCPCB and had a few minor errors (MIDI DIN pin swap, resistor silkscreen mix-up) that were corrected in subsequent revisions.

Software

UI Board Firmware

Firmware source is in Software/XVA1UserInterface/ and built with PlatformIO.

# Run from Software/XVA1UserInterface/
platformio run                  # compile
platformio run -t upload        # compile and flash
platformio run -t monitor       # open serial monitor (115200 baud)
./upload_and_monitor.sh         # flash then monitor

See AGENTS.md for a full architecture breakdown and development notes.

Use in Neovim

In order to use this project in Neovim, you will have to create the file compile_commands.json file by running the following command:

pio run -t compiledb

Synth Management

To manage the XVA1 (or XFM/XFM2) synthesizer's own firmware and programs, use xload-macos — a macOS tool for managing flash memory on XFM/XFM2/XVA1 synthesizers.

Project Structure

Hardware/       KiCad schematics and datasheets
Docs/           Photos of front and back of the board
Software/
  XVA1UserInterface/   PlatformIO project (all firmware lives here)

Status

Working prototype. Most parameters are implemented and editable. Patch saving is not yet implemented. The PCB design has gone through two revisions; the current version uses the XIAO ESP32-S3.

License

See LICENSE.md.