April 16, 2014
Now that I had a couple voices working, it was time to nail down the CV/gate controller and audio output. Up to now I'd been using an Arduino Nano and DAC8568 based circuit implemented on a temporary bread board for the CV/gate control, and the output of each voice went directly to a channel on my audio mixer. The control obviously needed to be implemented on a PCB and I wanted to have all the voice outputs combined with an on-board stereo pan/mix, providing the outputs on stereo pair of jacks similar to the Oberheim OB-X.
The design I came up with still uses the same ATmega368P microcontroller that the Aurdino Nano is based on, as well as the same DAC8568 and midi input circuit that I was already using, so I was able to continue using the Arduino code that I had already written for the bread board implementation. I didn't implement the USB interface that is included with the Arduino Nano, so for programming the microcontroller I switched to using an AVR ISP (In-circuit Serial Programmer). I also added a portamento circuit and fine tune adjustment for each CV output. The output section has a pan adjustment for each voice and a final output volume control.
As you can see, so far I've just built up 2 channels for the two voice boards I've built, and everything seems to be functioning well. Next up: Build the rest of the voices and get everything mounted in something.