Rust Language STM32L412 Ribbon Controller

Features

Three analog outputs

• RIBBON CV: 1volt/per octave scaled control voltage generated by the main ribbon
• GATE: 5 volt gate signal which is high when pressing the main ribbon and low otherwise
• MOD CV: mod-wheel like control voltage generated by the MOD ribbon, in [0v, +5v]

MIDI output

• Note on/off based on finger position on the ribbon
• Pitch-bend message bends the pitch when the ribbon is in between notes
• Mod: mod-wheel message generated by the MOD ribbon

Three pitch modes are available

1. QUANTIZE: notes are forced to be musical half steps, sliding around will zipper to new notes
2. ASSIST: when you first press a new note it is forced to be a musical half step, but continued sliding is smooth
3. SMOOTH: no quantization is performed, offers the greatest degree of pitch freedom but is difficult to play in tune

Glide control

• Adds portamento to the RIBBON CV signal
• This allows you to smooth out the steps when in QUANTIZE mode

Notes about the MIDI output

• This software assumes that the pitch bend range on the receiving instrument is set to +/- 2 semitones (this is typically the default)
  • If the Assist or Smooth modes seem crazy, make sure that the pitch bend range on your instrument is set to +/- 2 semitones
• The MIDI output signal sends note-on, note-off, and pitch bend messages to generate the smooth ribbon action
  • This works best with a mono instrument, and may act differently depending on the MIDI implementation of the receiving device
  • If the receiving instrument has non-retriggering envelopes, it will smoothly slide as expected
  • If the instrument has retriggering envelopes, each time you slide into a new note the envelopes will be triggered
• The MIDI output starts on a fairly low note
  • It works best if the instrument being controlled can be transposed to different octaves

Rear panel IO jacks and controls

• Output jacks for analog signals RIBBON CV, MOD CV, and GATE
• Standard MIDI OUT 5 pin DIN output jack
• MIDI CH channel select rotary switch
  • MIDI output is sent on the channel set here
• 9VDC IN power supply input jack

Calibration

• A trim potentiometer is exposed through a small hole so the device may be calibrated without disassembly
• Measure the RIBBON CV signal with a multimeter
• Set the MODE switch to QUANTIZE
• Adjust the trim potentiometer while playing alternating octaves so that the octaves are as close to 1.000v apart as you can get
• The MOD CV and MIDI output do not require calibration

Power supply

• A common guitar-pedal style center-negative 9 volt DC wall wart powers the device
• The circuit consumes approximately 20mA from the 9 volt DC power supply

Project status

• A prototype has been built and tested
• A handmade wooden body houses the components and provides a comfortable wrist rest while playing

Project goals

• Mostly just for fun and to explore embedded Rust
• Serve as a test bed for the Josh Ox Ribbon Synth
• Build a cute little CV and MIDI source