[sdiy] Proposed DSP board

[Robin Whittle]

A quick look at the 24 bit Motorola board:

http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=SYMP_SOUNDBITE

for USD$150 looks hard to beat for power, ADC and DAC channels, etc.

(Just wait for the USD to devalue . . . but will it devalue faster
than your own?  Every currency will be racing to devalue to prop up
its local industry, and as a natural consequence of every government
printing money for this purpose.)

My interest in dsPICs is in their cheap, 28 pin DIP, with dual audio
DAC models.

If you want to go to surface mount, spend a lot of money, there are
faster DSPs which handle more then 16 bits.  Doing quality audio in
16 bits is pretty tricky.

If you want to do 32 bit floating point audio, I guess there are
bigger DSP demo boards - and also current PCs are damn-fast at this
sort of thing, with Csound, assembly or I guess C.  Quite small
PC-compatible boards are available with four-core CPU chips running
at 3 or 4 GHz - for a few hundred dollars.  I guess that various ADCs
and DACs can be plugged into them via PCI or USB.

But if you want a device for a few dollars which takes up a
postage-stamp's worth of board space, and which can do prodigious
work on 16 bit audio, and have 16 bit audio DACs on board, in a DIP
package for convenience of servicing and small-scale production . . .
I think certain dsPIC models are impossible to beat:

  dsPIC33FJ128GP802

http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=8183&mid=14&lang=en&pageId=75

I have some samples but have not yet tried programming them.

It takes some time to figure out the assembly language programming
and IDE, but it is possible to do a huge amount of work with these
things.  Sampling at 44.1 kHz, you have 907 instructions to play
with.  A single instruction can multiply and accumulate, preparing
operands ready for the next cycle.

I did some development work for a client using a 33MHz dsPIC30
device, and found it very good.  The primary limitation is not having
a lot of RAM for reverb and the like, unless perhaps going to a 100
pin dsPIC and static RAM, which means higher costs, big SMD chips etc.

There are SPI RAM chips now - 256k bit from ON Semiconductor:

  http://www.onsemi.com/PowerSolutions/parametrics.do?id=2207

In principle, this could be used with a 28 pin DIP dsPIC, but when I
looked at the programming briefly, I decided it would be a lot of
mucking around and not very fast.

 - Robin