Board

3D Renders

Schematic & PCB

Interactive BOM

Audio Processing

• Raspberry Pi Compute Module 4 or Compute Module 5
  • Flexible memory options for cost optimisation
  • Optional WiFi
  • Very low latency (~2ms with ELK Audio OS)
• Pedalboard Soundcard — two channel differential I/O
• or HiFiBerry DAC+ ADC PRO — high quality stereo I/O
• USB-A host + Mini USB device mode (firmware update)

MIDI and Control Surface

• Raspberry RP-2040 with custom firmware (USB or WLAN update)
• 6 foot buttons (push, release, long/short press)
• 2 rotary encoders with push button
• 2 expression pedal inputs
• 8 RGB LED rings around each foot button
• 2 RGB status LEDs
• STEMMA I2C connector for 2 OLED displays
• I2C EEPROM for config storage
• Flexible MIDI I/O: DIN 5, 3.5mm TRS, header pins, USB MIDI

Power Supply

• 6–28V DC input (standard pedalboard PSU) with 3A buck converter
• USB powered option for MIDI module
• ORing support between onboard PSU and USB power

Design Decisions

• USB 2.0 only — 480 Mbps is more than sufficient for audio (stereo 24-bit/192kHz ≈ 9 Mbps) and MIDI. USB 3.0 would add cost, routing complexity, and require a 4-layer PCB — with no practical benefit for this use case.
• 2-layer PCB — keeps manufacturing cost low and the project accessible to makers. USB 2.0 signal integrity is manageable on 2 layers with careful routing and short trace lengths.
• Dual-processor architecture — the RP2040 handles MIDI control with instant startup, while the CM4/CM5 runs ELK Audio OS for audio processing. This separation ensures the control surface is always responsive, independent of the audio OS boot state.
• Modular design — the board works as a standalone MIDI controller without a CM4 installed, or as a full audio processing platform with CM4/CM5 + soundcard. Common components and existing modules (HiFiBerry, CM4) keep the BOM accessible.