Microcontroller/Arduino CV keyboard/sound source

[Rolbista]

Hi guys. In my work I try to merge circuit bending, upcycling and real synth DIY to construct fully (well not really but more on that later) musically viable instruments out of otherwise useless keyboards, modules and gear. Usually I would just go about it by taking a signal, square it up with a comparator, add some dividers to get suboctaves, some fuzz pre and post filter and I would call it a "synth". And while to most people it sounds synthesizer-ishly enough, such solution does not allow any kind of pitch bend, filter tracking, envelope retrigger or vibrato, not to mention that note range is limited to what the keyboard can deliver. Long story short - at the moment expression with such a machine is limited and I decided to design/put together my first proper synth. It just so happens that I've managed to come across two CEM3391 Curtis voice chips which contain an ADSR, two VCAs and a 24db VCF so most of the synth is already put together in one IC. What remains however is sound and control voltage generation. As the only CV keyboard project I was able to find was MFOS Single Bus keyboard (which looks waaay over my head), and since all this business with tuning analog VCOs kind of scares me and seems messy, I figured it would be both simpler and more elegant to just make a CV keyboard using a diode matrix and a microcontroller that would deliver a stable voltage of easily fixed value. It would also be nice to use the MCU as a waveform generator simultaneously. Now, I should mention that I have no experience in programming and debugging these things (just a few lessons in C++ in college) but something like an Arduino seems to have a big enough community to somehow help me through. I am making this post because my google-fu has not turned up results suitable for my needs and this whole concept seems like it should've been done before by someone so I wouldn't like to reinvent the wheel here. I just need to be pointed in the right direction, I'm not afraid of doing further research. This is going to be my most ambitious project yet.

Aims and restrictions of the project:

- use the CEM3391 IC (24db VCF, ADSR, dual VCAs, all voltage controlled) with the DEV91 Digisound board

- available supply voltages: +12/+5/-5V. Well, anything that can be regulated from 16-15V, the negative 5V will be made using an ICL7660 charge pump

- use an existing diode matrix from a small (toy or mini to midsize keys) salvaged keyboard. Preferably 3-3,5 octaves

- pitch wheel with up to +/-1 octave bend. Looking for ideas for a DIY pitch wheel

- Arduino/uController/whatever IC needed serve as an oscillator/signal source. Preferable waveforms - pulse, ramp, tri/sine (don't mind analog waveshaping if necessary), number - at least 2 OSCs + subosc (optional, can be added easily by analog means), preferably 3 OSC. Detune, sync and pitch bend required, also modulation with an LFO. I was thinking of just building analog VCOs, but +/-5V range limits me here. Or maybe It would be possible? If so, please enlighten me.

- Arduino/uController/whatever IC output CV corresponding to played note with pitch bend taken into consideration. I need this to drive possible additional analog VCOs and for filter 1V/octave tracking. Range will probably have to be 5V but will have to be scaled to -5V/+5 to fully modulate the filter. Octave range switches like on a MIDI keyboard would be nice too.

- output gate (optional, if I have to, I guess it can be derived from signal)

- MIDI input would be nice but is not a priority

- portability. The size of something like a MicroKorg is what I'm aiming at, maybe slightly smaller so I can just pack it into a bag and head to the jam space.
Here is the list of thing I have considered already and why they are not good enough.

- PICsynth chip - scans the keyboard, nice waveforms, almost what I need BUT it doesn't output CV or gate and does not support pitch bend so that leaves the CV keyboard unsolved

- dsp G1 chip - MIDI ready but no CV output, and it would force me to make my keyboard a MIDI one

- Electric Druid Waverider - good too, but still leaves the CV keyboard unsolved

- Make the keyboard a MIDI one, then make a MIDI-CV converter, then drive VCOs and the rest with it - that's what I would like to avoid because it pretty much goes against my minimalist philosophy here, gets complicated

- buy things like Shruthi, Anushri or some other kit - well, too expensive for me, if I had money for a Shruthi I wouldn't bother with building.

- I also just stumbled upon this: Integrated Keyboard Controller (IKC) DIY Project but I don't really need all the features and looks complicated too

I'll be grateful for any contributions, I hope this post makes sense and describes my intentions and needs well. Cheers, Wojtek


*EDIT*
Okay, looks like it was too much to ask. Well, anyway, I guess I'll keep you posted anyway, I have ordered an Arduino and I'll see what I can do with Mozzi library. For now the priority will be getting one oscillator and CV output.