AVR-VCO: Microcontroller-based VCO (3HP - FR4 panel)
An updated version of this module is now available here - this is likely to be the final run of the 3HP module
HEAR IT HERE: https://soundcloud.com/yorkmodular/avr-vco-demo
SIMPLICITY IS KING.
If you want an all-singing, all-dancing VCO with lots of bells, whistles and foghorns well, there are plenty of them on the market so feel free to go take a look at them. However, if you want something simple and hackable then we've got you covered.
Analogue VCO cores are a pain to build so this is based around a microcontroller instead - cheating? Maybe so, but it's pretty damned versatile and if you have the knowledge to program microcontrollers then you can hack it to your heart's content.As supplied, the module can provide six different output waveforms: sine, triangle, square, sawtooth, something pulse-ish and digital noise - waveform selection is either via the pot _or_ it can be voltage controlled. If you want to get down and dirty with the code then you could easily replace the wavetables with something else.
It'll track 1V/octave pretty well over 5 octaves, this being governed by the fact that microcontrollers tend to get a bit upset if you feed more than 5V to their input pins. There are three inputs, two of which have inline attenuators - by default, these control tuning, output waveform and pitch CV.
In addition, these modules were designed to fit behind 2HP panels however in some cases there's a risk of interference with adjacent modules particularly if these modules have PCBs which are the full width of their panel, so they're supplied with a 3HP panel as standard.
The output waveform is a filtered PWM signal - the output filter has a cutoff frequency of 1.6kHz which gives you a usable range of 5 octaves - it's a lot cheaper than a DAC ... The schematic, source and BOM for the module can be found here, as can panel files: https://bitbucket.org/yorkmodular/avr-vco-diy/src/master/ - all the bits you need, including a pre-programmed firmware chip, are included .
The firmware source has a permissive license, so feel free to hack on it - updates and modifications are most welcome
The module is ~47mm deep, so please bear this in mind if you're using a skiff-style system. The module is finished with Alpha potentiometers and Befaco micro knobs. Power cable and mounting hardware are also provided - the 3HP panel is fabricated from 1.6mm FR4 (aka. PCB material).
If you'd prefer to fab your own panel then you can find the design files in the Bitbucket repo.