MCO Driver using an ATtiny 84

I’ve been working on the Mixed Control Oscillator recently, it will be using an ATtiny 84 AVR chip from Atmel in the final form factor (so far it’s been running fine on my dev board using an ATmega644P, which is a bit overkill for such an application).

Here are the final specs:

For the driver itself (the AVR chip):
  • Precise control of the frequency via SPI. It is based on the MIDI note numbers, but with every cent between two semitones being accessible (1 cent precision), allowing frequency sweeps and continuous digital modulation.
  • Analog input for modulations (1V/octave, 5 octaves range).
  • Global detune (from reference A4@440Hz, with 1 cent precision).
  • Portamento (work in progress), with two modes: constant time & constant slope.
  • Hard sync input & output.

For the analog part:
  • Saw, Pulse and Triangle outputs.
  • PWM inputs.
  • Special triangle mode where the slope follows the PWM (work in progress). This would allow smooth transition from saw/ramp to triangle using PWM.

The ATtiny84 on AVRFreaks: