[sdiy] FracRak digital module?

[Barry Klein]

Dave Jones on the AmpHour podcast brought up a very good point:
Why aren't there fpga's with a small pin count?

Barry

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Scott Gravenhorst
Sent: Friday, April 22, 2011 7:57 AM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] FracRak digital module?

David Betz <dbetz at xlisper.com> wrote:
>I'm thinking of building a FracRak format modular synthesizer and 
>would like to find a module in that format that has some analog 
>inputs and outputs and a microcontroller or DSP with open source 
>firmware that can be loaded with custom code. Actually, something 
>with an FPGA would be even nicer. Does anyone know of something 
>like that that would fit into a modular system? A few years ago 
>there was a module called PSIM-1 that had a PIC chip but it is no 
>longer being made. 

If you're interested in PIC processors, I'd look at the Microchip dsPIC
device which is 16 bit and can have nice audio capable devices right
inside the chip such as ADC, DAC and UARTs.  These have some true DSP
capacity with a degree of parallelism allowing for such things as
single cycle per tap FIR filters.  They are even available in DIP.  I
understand there is a useful free C compiler available as well.  Not
sure about "open source firmware", but I would think/hope there is
public domain code out there that could be used directly or modified to
your special purposes.  (Please note that I'm an assembly language guy)

Since you mentioned FPGA (as even nicer) I would consider using an FPGA
development board behind the panel.  They can be very economical
because they are subsidized by the FPGA mfr.  These boards can have
some nice peripherals already available (such as DRAM, DAC, ADC).  As
you may know from my previous postings, I use FPGA development boards
to implement monophonic and polyphonic synthesizers.  It's been a while
since I've looked at that market, but when I bought mine, the
bang-for-buck factor was quite high (IMO).  I use Xilinx, but I'd bet
there are similar offerings for Altera.  As for "open source", not sure
what you would mean in an FPGA world, but at least for Xilinx, the
"compiler" can be free (or paid for to get somewhat more advanced
features).  In fact, the software I've used to generate my designs is
all $0.00 stuff and does the job quite well.  The boards I have all
incorporate a Flash bit-file loader that can be user programmed to
allow the device to assume functionality when powered on.  The downside
of the boards I have is that the FGPAs are all BGA package and not
easily soldered by human hands, but they have the advantage of being
potentially internally large.

Alternatively, if you are interested in making your own PCB, there are
some FPGAs available in TQFP that are still large enough to make a
reasonably powerful polysynth (16 voices...).

-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- FPGA MIDI Synthesizer Information: home1.gte.net/res0658s/FPGA_synth/
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- When the going gets tough, the tough use the command line.

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy