[sdiy] dsPIC33 question..

[Seb Francis]

Tom Wiltshire wrote:
>
> 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?
>

Well should definitely be universal - that's the plan.  Since I'll be 
using as much SMT as possible I should have plenty of space to include 
lots of input buffers which can then be soldered in as required.  The 80 
pin dsPICs have 69 I/O pins which breaks down something like this:

SRAM for 1.5s delay - 27 pins
Stereo CODEC - 4 pins
ICSP/ICD - 2 pins
2x Clip LEDs - 2 pins

Leaving 34 pins for control inputs, up to 24 of which can be CV inputs!

Is it worth having some as buffered outputs, for operating more LEDs, etc??
Or maybe just unbuffered direct access to some of the I/O pins would be 
more generally useful.  Particularly the SPI pins, so multiple boards 
could be hooked together with communication (albeit relatively slow) 
between them.  Also with SPI one could drive external serial DAC(s) 
which could then output DC-coupled CVs if desired.

I'm wondering about MIDI input as well .. I wasn't planning to use it 
myself as I like the immediacy of the unit responding exactly to where 
the knobs and switches are set and to what external voltages are coming 
in.  But the dsPICs have UART built in and it wouldn't take much board 
space to add an opto-isolator and a couple of resistors (although not 
sure opto-isolators come in tiny packages... might have to be DIP).

So what's the thoughts out there?  Is a MIDI input option worth having?

Any other wish-list ideas for I/O capability??

> 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.

Good that the code is identical :)

The DMA sounds interesting.  I'm hoping this will shave a few CPU cycles 
off here and there.


>
> 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.

Yeah, and plus the normal PCB headers have a relatively low number of 
connects and disconnects before the contacts stop being so springy.  Not 
sure about RJ11 though as I haven't seen any panel mount sockets and I 
don't want to tie the PCB to a particular panel layout by using PCB 
mount panel components.

It actually only needs 5 pins for a ICSP/ICD so maybe a normal 5-pin DIN 
socket would be fine .. or perhaps one with the pins in different places 
to stop people plugging MIDI leads into it!

Seb