MIDI2CV v1.0

The ACXSynth MIDI2CV is a simple to build DIY MIDI to CV/Gate interface

This module circuit and firmware design was developed by Alain Coupel of ACXSynth. His design and firmware is used here with permission.

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ACXSynth MIDI2CV Features

12bit DACs with Intersil tunable opamps mean great CV accuracy (many commercial MIDI-CVs have only 8bit DACs)

This module has three modes, selectable by the mode select switch. This switch is a THREE position switch (Up, Centre, Down) and its functions are as follows:

Up = Polyphonic 1 Channel
Centre = Polyphonic 4 Channel
Down = Monophonic 1 Channel

In the Poly 1 or Poly 4 states, the 8 lower output jacks function one way, as indicated, and in the monophonic mode, they function another way for full control of one voice. That is, there is one "full" channel of CV (ie: with mod wheel, keyboard velocity and normal CV), a gate and a trigger output.

A special note about operation in Monophonic mode:

The way in which note/gate data is handled is unique for most MIDI converters, and different people like different styles, so, I will do my best to explain exactly how this one works, here.

The module operates in LEGATO operation during monophonic mode. This means that if you slide two notes together, the gates will tie together. In other words, if you want two notes to generate two independent gates, you MUST completely let go of the last note before starting a new one. The "TRIG" output of the module in monophonic mode always sends a trigger pulse whenever a key is hit, so, in this way you can patch it up to get STACCATO style playing be re-triggering your envelopes, if that is your fancy

If you play one note and play another while still holding the first note, it DOES revert to the note played previous.


Sync jack:
This jack outputs an analogue version of the MIDI clock in the digital data stream. It is 24ppqn and can be divided down for use driving sequencers and the like. It can be used alongside the run/stop and reset outputs to control a sequencer while playing in Monophonic mode.

LEDs down the centre of the lower jacks:
Each of these LEDs corresponds to the respective Gate/Trig/digital output.

MIDI In jack:
This is where the user plugs their MIDI cable into.

LED to the left of the MIDI input jack:
This LED is a status indicator for the module. It is lit when the module is first initialised and has yet to detect a MIDI channel. When MIDI clock is being received, it blinks along with the beat.
!!READ THIS!! -- HANGING NOTES:

In Monophonic mode, if you bang a whole bunch of keys at once, the module will sometimes get the GATE output stuck open. 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. :)

You have been warned! I am the full-disclosure type and while 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.
Schematics