Introduction
The ACXsynth MIDI2CV is a DIY (“do it yourself”) MIDI to CV/Gate converter for analogue modular
synthesis. This project was born out of the need for an accurate and readily available eurorack DIY
MIDI-CV project. As a user of modulars myself, I struggled during my DIY modular system’s infancy
to find a MIDI-CV interface I could build myself. The only solutions were too expensive, did not fit my
needs or were out of reach at the time.
Rather than develop and code a module from scratch myself to solve the problem, I knew about Alain
Coupel of ACXsynth’s great PIC microcontroller projects for synthDIY hosted on his site ( acxsynth.
com ), so, I asked him if I have his good graces to make a eurorack-centric DIY module out of his
great design. His designs are presented in a mostly open-source 5U format design philosophy, so,
unfortunately the design did not fit into eurorack without a redesign of the hardware.
When I first began this project in January 2013 or so, I did not expect for it to take shape the way it
did. A number of bugs in the firmware were unearthed by people on the forums in which the project’s
development were publicised. Me and Alain communicated through many weeks of long-distance
email tag and worked through much bug-fixing before finally arriving at the v4.0 firmware which you
now see present in this hardware design.
This new firmware adds a number of features and tweaks not present in the older open-source
version on Alain’s site. Do not try to layout your own panel from the panels on his site (or
Re:Synthesis’ for that matter.) The aforementioned panels are for older versions of the firmware and
will not work with this hardware design.
Please use the 8HP eurorack and eventually 4U dotNET format panel renders present on the
hexinverter.net project page as reference when laying out your own panel for this project!
While Alain and myself strived for perfection with the firmware and eradicating all of the code
bugs,
one bug remains which much problem solving on Alain’s part could not rid of. We have ruled
it out as a shortcoming of the rather modestly specced microcontroller used in the design.
If you
are considering this module I urge you to read about this bug and determine if it’s a problem for you
before purchasing:
In Monophonic mode (only), if you bang a whole bunch of keys at once, the module will sometimes
get the GATE output stuck open for a few keystrokes. Seeing as how this occasional error is
Monophonic mode, this shouldn’t be a problem for most users since you play one or two keys at
once only in Monophonic operation, but, if it is a problem for you I strongly encourage you to abstain
from building one of these as it is a problem that cannot be solved without deleting other features
(to free up processing power).
The beta testers agreed that it is not a huge issue, but you may feel differently, which is why I am
telling you. With regular playstyles, it should not be an issue. I can only get it to happen when I’m
trying to make it happen. The beta testers and myself could not replicate the issue during normal
play.
I wish that the firmware was 100% perfect in every way, sadly the little PIC microcontroller isn’t
quite up to doing everything it does do in Monophonic mode with absolute perfection.
