[sdiy] dsPIC33 question..

Tom Wiltshire tom at electricdruid.net
Wed Nov 12 13:50:22 CET 2008


It sounds like a great box.

Please try and keep the hardware as universal as you can, 'cos people  
round here have been talking about a universal digital module  
platform for some time, and it sounds a bit like you're designing  
one. Audio in and out, plus a load of CV and digital inputs for  
control, with a decently powerful processor and some external RAM -  
sounds pretty universal, right?

I've used the dsPIC 33FJ128GP802 recently for the DWGS dual  
oscillator project that I'm working on. It's one of the new 28-pin  
chips with a DAC onboard, so it's great for what I need.
I've found the 33F chips very easy to use, and no different from the  
30F series, except in details (and power consumption). The 33F chips  
have DMA channels for example, which is something new to learn.  
Certainly the code is identical.

Definitely stick a ICSP socket on it. My programmer uses RJ11 plugs  
to connect between the programmer and various ZIF sockets for  
different uPs. Consequently, I've started putting RJ11 programming  
sockets on my projects. The plugs cost more than a simple 6-pin  
header, but it's much easier to plug in and out.
I agree with you about USB too - for now, it's too much to learn.  
I've wondered about getting stuck into it and trying to do USB MIDI  
like a lot of modern synths have, but frankly I have enough else to  
learn already!

Keep up the good work, Seb!


On 12 Nov 2008, at 03:01, Seb Francis wrote:

> Hi,
> 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!
> Seb
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