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The Wavetable VCO is a digital oscillator for modular synthetizers, based on an ATMEGA1284P microcontroller. There are 2 different versions of this module, the 8-bit one and the 16-bit one. The 8-bit version has 500 waveforms stored on the microcontroller internal flash, the 16-bit version has 250.

Pitch - It's pitch is controlled with the standard 1 v/oct with 5 octave range. A potentiometer in the front panel controls the offset voltage giving another 5 octaves in pitch range.

Modulations - It has four digital modulations. Each of them can be controlled with a voltage source and/or a potentiometer and can be selected by a push button.

Waveforms - The 250 waveforms in the 16 bit version and 500 in the 8-bit one, can also be selected by a potentiometer and/or a voltage source. Another pair of CV/potentiometer controls a blend between waveforms.

Sync - It can be hard-synced with any other oscillator.

The module will be compatible with Doepfer's Eurorack system. More information here. It needs the +5V rail on the power supply.

Effects

Bit Depth: reduces the vertical resolution of the waveform. The CV/potentiometer controls the number of bits taken.

Sample Rate: reduces the horizontal resolution of the waveform. The CV/potentiometer controls the output sample frequency.

Sample Kill: makes 0 the value of the output waveform at a certain rate. The CV/potentiometer controls the rate of the modulation.

Sample Polarity: inverts the output waveform at a certain rate. The CV/potentiometer controls the rate of the modulation.

Project Status

The project is currently in prototyping phase. The last prototype has all the features mentioned above except the 1 v/oct control for the pitch and it has only a few waveforms. The next stage will be building a robust module in order to fine tune the controls and add all the waveforms.

The PCB has already been designed and it will look something like this: PCB Preview

This is the 16-bit version with an AD669 digital-to-analog converter. All parts except the AD669 are through hole.

Digital-to-Analog Converter

The AD669 is a very good precision DAC but is expensive and not so easy to get. That's why I'm making the 8-bit version with a DAC0800, wich is a "jelly bean" DAC that has been around for decades and it's probably the most common DAC on vintage digital audio equipment.

Links

tabulaRasa (some ideas and code taken from here, thanks to Greg Surges for the inspiration)