[sdiy] Old Computers

[Batz Goodfortune]

Y-ellow Scott 'n' all.
         I was probably the originator of that thread way back when. And 
while I've achieved sod-all in this direction I have a few hints.

The parallel port is only 8 bits so you'd need to hand-shake it. Meaning, 
whatever throughput you get will be halved.

2 A simple D-A such as this would have no anti-aliasing filters. More to 
the point, it would be rather difficult to do unless you could guarantee a 
sample rate. Which is going to be a bit difficult in it self because the 
printer port is async.

3 Forget creative crap. Look for el-cheapo Crystal reference cards on eBay. 
I've never paid more than $5.00 for one. All of everything is known about 
these cards since you can (or could) download the complete design and specs 
from their web site. Having that NFO should make life a lot easier.

Armed with the above, not only do you have a system you can deal with at 
the bit-level, but you also have all the nice, funky bits. Like 
anti-aliasing, over-sampling, and interpolation. Depending on the card, you 
might get a whole pile of cool stuff with it. Like an effects engine or 
even a synth in it's own right. You'll almost certainly get a built in OPL3 
type FM synth. And you don't even have to worry about tricky board layout 
to avoid grounding problems and stuff like that.

Most of these crystal Semi cards were made as reference designs for their 
development and marketing. However they were marketed as cheap ISA sound 
cards presumably to get production costs down. There are lots of them and 
they're dirt cheap. In fact you'll probably find most of them in garbage 
mountains these days. Which IMHO is a damn shame.

The irony is that they're a pain in the ass to use in a cheap-old computer 
system runing BOSH or Linux but as a development system to hack and work 
with they're brilliant. For that matter, why not hook one to an AVR?

Be absolutely Icebox.


At 11:01 AM 5/29/05 -0700, Scott Gravenhorst wrote:
>With the introduction of AVRSYN, I remember a post not that long ago by
>someone asking if anyone had attempted to use an old PC to make some kind
>of synth.  I have several of these myself, 486-66 and AMD 5x86-133.  I did
>a little bit of research and found a website where someone had done a DSP
>using a soundcard and a special 16 bit DAC ISA card that he designed (this
>is because, according to his information, a Creative SoundBlaster does not
>allow a program to directly send values to it's 16 bit DAC and there are
>only one 8 bit and one 16 bit DMA channels, but 16 bits was required for
>both input and output).  My sound cards are all Creative devices and I'd
>prefer the simplicity of being able to directly manipulate the DAC.
>
>So I looked at Jarek's site and I see he uses a homemade 16 bit DAC, driven
>by 2 CMOS latches.  I wondered why we can't do the same with a printer
>port.  That totally removes the need for a soundcard altogether and the
>"dongle" would be extremely simple and trivial to program.  PCs have a
>built in programmable interrupt timer that can be set to interrupt
>regularly and an interrupt service routine could then calculate the next
>DAC value and present it.
>
>Has anyone approached this at all?
>
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