I’ve built my MCVI MIDI to CV synth module, the one I breadboarded here.
It handles a range of 88 MIDI notes, corresponding to a standard piano keyboard, using a 12 bit DAC. CV output is 0 V (for MIDI note 21, A0) to +7.25 V (MIDI note 88, C8). Note selection in case of multple keys pressed is governed by a switch selecting lowest note, highest note, or most recent note priority.
Pitch bend CV range is 0 to +1.0 V (0.5 V when centered). Velocity and modulation CV range is 0 to +4 V. Gate, trigger, and clock outputs are +5 V; trigger and clock pulse width is 20 ms.
The module is built around an Arduino Nano. The sketch uses the standard MIDI and SPI libraries.
Surprisingly, it seems to be a little off from 1 V/oct. That’s fairly easy to fix, just change a constant in the code, but it was more accurate on the breadboard. Hm.
Quick test video:
Schematics, Gerbers, and documentation are here.