Emiuet

Emiuet (EUB-04)

Fretboard-style MIDI instrument for guitarists.

What Emiuet is

Emiuet is a 6 × 13 fretboard MIDI controller built around the way guitarists think: strings, fret positions, chord shapes, voicings, and controlled expressive gestures. It is not intended to become a general-purpose pad controller or a piano-style keyboard.

The thirteen positions preserve familiar guitar-derived voicings without forcing octave shifts or omissions. Expressive controls are deliberately constrained so that performance remains predictable: Pitch Bend is upward-only, and the optional MPE-style mode separates strings by MIDI channel rather than attempting a fully general per-note control system.

Emiuet is part of Emnyeca's Utility Build Series (EUB). The project prioritizes musical intent, reliability, and a clear physical mental model over feature breadth.

Playing surface and controls

• 6 strings × 13 positions: 78 low-profile keys
• Three sliders: Velocity, CC#1 Modulation, and upward-only Pitch Bend
• Constrained stringwise MPE-style performance mode
• Minimal OLED feedback designed to avoid distracting from performance
• USB MIDI, Type-A TRS MIDI OUT/IN, and BLE capability
• Auxiliary USB HID Keyboard mode (TYPE)
• One RGB LED under each key for fretboard visualization

TYPE is a desk-convenience feature for short text, navigation, and shortcuts. It reuses the physical matrix but does not change Emiuet's identity as a musical instrument. See USB HID Keyboard Mode for the complete layout and Fn layer.

Rev.B hardware summary

Rev.B simplifies Emiuet into a USB-powered Device/UFP:

• ESP32-S3-MINI-1 using native USB
• One USB-C port for 5 V power, USB MIDI, USB HID, and firmware flashing
• Persistent USB MIDI + HID Keyboard composite device
• USB-C CC pull-downs with a comparator that tracks the Source current advertisement
• No USB Host, DRP, Host VBUS sourcing, internal battery, charger, or PowerPath
• SK6812 MINI-E ×78 on one data chain with a 3.3 V-to-5 V buffer
• Firmware-limited LED brightness/current based on conservative USB power budgets

Mobile use is supported with an external USB power bank. A 3 A Source advertisement does not raise Emiuet's internal design ceiling above approximately 5 V / 1.5 A.

MIDI and RGB behavior

Performance logic remains independent of individual transports. MIDI generation must not block on USB, TRS, or BLE output. Incoming USB or TRS Note On/Off messages can drive fretboard visualization through a transport-independent LED state layer.

The external protocol for device-level LED settings such as global brightness is not defined yet. Standard musical Control Change messages are not repurposed for device configuration; a future explicit protocol may use SysEx.

Hardware and firmware sources

• Current Rev.B schematic draft: hardware/kicad/Emiuet.kicad_sch
• Historical Rev.A schematic: hardware/kicad/Emiuet_RevA.kicad_sch
• Rev.B GPIO allocation: docs/pinout-v3.md
• Current design decisions: docs/decisions.md
• Firmware: ESP-IDF 5.3.4 + FreeRTOS; OLED rendering uses u8g2

The checked-in PCB layout is historical Rev.A data and was not updated with the Rev.B schematic. Rev.B placement and routing require a separate PCB redesign.

Project status

The Rev.B schematic is an early architecture draft, not a fabrication-ready release. USB-C current detection, reset/boot, the RGB buffer, and the OLED connector are drawn; power and MIDI circuits are incomplete, and the matrix, sliders, buttons, and protection circuits still need implementation. Component selection, footprints, PCB layout, and physical validation remain open engineering work.

License

To be determined. An open-source-friendly license is planned after prototype validation.