[sdiy] dsPIC33 question..

Seb Francis seb at burnit.co.uk
Wed Nov 12 04:01:44 CET 2008


I'm just starting to look at designing a new digital delay / flanger 
(like my 4xD, but this one will be a 2xD with just 2 channels).

Actually what I really want to make is a generic PCB that can be used 
for lots of difference digital synth modules.

Unlike the 4xD it will have no MIDI, no display and no settings memory.  
Instead it will be fully controlled by lots of CV and on/off (gate) 
inputs.  Either external inputs and/or panel controls can be used as 
necessary ... pots for CVs, switches or buttons for on/off inputs.  So 
this is something that will sit in a modular synth.

Basic components will be:
- dsPIC
- SRAM enough for 1.5s audio
- Stereo CODEC
- VCAs for feedback loops (x2)
- Audio, CV, Gate I/O buffers

So anyway I'm at the stage of deciding which dsPIC to use and looks like 
I'm going to have to go for at least 80 pin package as unfortunately 
anything less shares all (or almost all) of the A/D inputs with the only 
16-bit I/O register which I need for efficient access of the SRAM.

I also want to go for something a bit faster than the 4xD (30MIPS) as 
this was getting pretty near the limit in some circumstances, and this 
was without any CV input processing.  So I reckon I will need something 
that goes at 40MIPS.  And of course it must have a CODEC interface

Without going to 100 pin packages, this narrows it down to either a 
dsPIC33FJ64GP708 or dsPIC33FJ128GP708.

So, now my question .... what is the code compatibility like between 
dsPIC30 series which the 4xD uses (specifically the dsPIC30F6012A), and 
the dsPIC33 series.  I'd like to avoid too much headache porting the 
code over if possible.

I'm also wondering about soldering, as before I used 0.8mm pitch parts, 
and now everything is down to 0.5mm pitch.  But I'm guessing this will 
be manageable as I think the CODEC ICs I used before were 0.65mm and 
these weren't too bad to solder.  Actually I even wondering if the 0.4mm 
parts are doable - anyone have experience soldering this kind of stuff 
with a normal soldering iron?

Anyway, quite excited about making a generic digital module for my 
modular - I've only got a small amount of rack space left and I'd like 
it to be used well.  I'll probably stick an ICSP/ICD socket on the front 
so it can be re-programmed into something else whenever I feel like it!  
I stopped short of thinking about USB for updating the firmware .. don't 
want to cause myself pointless extra work!


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