MIDI to CV Converter

This MIDI to CV converter is the perfect interface between your computer or iPad and an analog synthesizer (e.g., see https://www.thingiverse.com/thing:2704888). It can independently drive up to three oscillators with 1V/octave CV inputs. (Connection to an iPad requires the USB camera adapter but is well worth it given the wide variety of great MIDI sequencer apps.)

This device has the following features:

• USB MIDI Interface
• Three channel Note CV output (88 keys, 1V/octave, MIDI channels 1-3) using a 12-bit DAC
• Configurable note priority for each channel (Top Note, Bottom Note, or Last Note Priority)
• Note scale factor calibration configurable in software
• 5V Gate/Trigger outputs, where each channel can be independently configured to either output a gate (output high for entire length of time that note is on) or trigger (20 msec pulse each time a new note is initiated)
• Velocity CV output (0 to 4V) for each channel
• Pitch Bend CV output (0.5 +/- 0.5V), which can be configured for channel 1, 2, or 3
• Control Change CV output (0 to 4V), which can be configured for channel 1, 2, or 3
• OLED user interface, used for setting parameters and saving to EEPROM

This device uses the Teensy 2.0 USB development board. The schematics and assembly instructions can be found at: https://github.com/elkayem/usbMIDI2CV_MC.

The 3D printed panel must be printed with supports for the OLED screen mount. There is a recessed area on the back side of the panel that fits the screen mounting shape. I recommend picking up the screen by DIYMall, as the hole pattern was designed for that screen. Others may fit as well. Supports are not required for the case.

The panel includes raised text, and so must be printed with two colors. Most slicers include a "pause at height" plugin, which will move the hot end out of the way and allow you to switch filaments. The panels are 3mm thick, and the letters are 0.45mm thick. I printed with 0.15mm layer thickness, allowing the letters to be printed in three layers. Add the command to pause after you finish printing the 3mm layer, so you can change the filament color. (One tip: If you find that your printer is disabling the stepper motors after pausing, you may need to insert M84 S0 at the start of the G-Code. I did.)