MIDI 4+1

A DIY Arduino-powered MIDI to 4x CV/gate interface in 6HP, with both polyphonic and monophonic voice allocation modes.

Arduino code | 3D model | YouTube demo | Muff Wiggler | Lines

Features and limitations

• MIDI DIN input and 4x CV/gate outputs with gate LEDs.
• Button for cycling through four different modes, with coloured mode LED:
  • Poly (red): four-voices polyphony with priority to last, LRU strategy and voice stealing;
  • Poly-first (orange): four-voices polyphony with priority to first and first-available strategy;
  • Split poly+mono (green): split keyboard with three-voices polyphony on the left, and monophony on the right (priority to last);
  • Split mono+poly (yellow): same as above, but flipped.
• Additional gate output that stays high while at least one polyphonic voice is active (logic OR), useful for single-filter setups.
• Voices lock with a long-press of the mode button: all gates of currently held polyphonic voices stay high, ignoring key releases until next reallocation.

The DACs range is 0-4V, so only the 4 center octaves are covered. The get more, it is necessary to add amplifiers on CV outputs, which will probably require a better DACs calibration process. Split modes splits the keyboard on middle C. Both lowest MIDI octave and split octave are easily configurable in code.

Circuit

The following is just a hint for a possible circuit implementation.

Pictures

Thanks

• Emilie Gillet's CVpal (polyphonic voice allocator and monophonic notes stack)
• Befaco MIDI Thing
• François Best's Arduino MIDI Library