[sdiy] dsPIC with on-chip audio DACs

[Eric Brombaugh]

Seb Francis wrote:
> These look great.  I feel some digital modules for my modular coming 
> on... super-saw oscillator, cloud oscillator, fancy LFOs, digital noise, 
> etc..  In fact maybe just make a single design with a rotary switch to 
> select which software to load?  - Have to use some fancy colour coded 
> labelling for the socket functions with each software (or a little LCD 
> screen per socket!)

Sounds pretty cool. Surprisingly, even with the limited pin-out on the 
28-pin package there's still plenty of I/O left over after you've used 
the DACs, ADC inputs, crystal oscillator and dedicated power pins. 
Should support a fair number of bells & whistles.

> Shame the ADC isn't quite up to audio spec (max 12-bit resolution).  
> Still fine for CV control (up to 10 CV inputs!), and actually probably 
> useable for the sort of audio one normally gets within a modular.

That is a bit of a problem. You may be able to improve the resolution 
some with dithering and internal filtering though, but I've found the 
12-bit operating mode up to the task of most CV input applications. If 
you _really_ need better accuracy, these parts do include the SPI andDCI 
peripherals, so you could hook to an external ADC or codec. 
Interestingly, since this part includes peripheral pin assignment the 
SPI, DCI and the on-chip DAC can be used simultaneously. 2 channels in, 
4 channels out anyone?

> I noticed they also do the dsPIC33FJ128GP802 with double program memory, 
> if developing something really complex (like a 10-in-1 modular synth 
> module for example)

You could do some fairly complex things with that much memory. The 
little test I've got going right now uses only about 12% of the flash 
and almost none of the SRAM on the 64k part, and that includes 
setup/support code that would be common to any functions you were to 
stuff into it.

Eric