building a sound sampler for cryptophone application...

My old uncle - a retired electrical engineer - has gone back to
night classes to learn electronics.  His class has to do little
projects that they pick themselves; nothing too advanced yet -
his last one was a musical door-chime...

Anyway, he was asking me for ideas for projects to build, and believe
me I've got dozens :-)  The one that I think is of most value to most
people, if he designs a simple circuit for it that I can publish,
is a cheap sound sampling interface .... which we can happen to
steal for our various cryptophone projects...

Here's how I see the design:  it feeds data into a (probably IBM PC)
parallel port (has to be the bidirectional kind, a plain printer port
clearly won't work), and *it* supplies the timing, ie the PC reads from
the port when the flags say data is ready, and no more data will be
presented to that port until n uSecs later - I foresee it supplying
data at either 8000 bytes/sec or 4000 bytes/sec if the former is too
fast for a PC to handle.

Putting the timing in the sampler frees the PC from a horrendous overhead
in sampling at accurate times, and would make it trivial to feed the
4000Hz samples into code like 'shorten' which would then be shoved down
a v32bis modem quite comfortably.  At a cost *much* less than any
commercial sampler: this thing is built from: a battery; a box; a DAC;
a 7$ microphone; a parallel port driver; a crystal, and a counter.
And that's it.  Dead cheap and easy to build, I hope.

What I'm writing here to ask is where can I get info on what chip to
use to feed data into a PC down the bidirectional parallel port, and
how do you drive the chip and what are the pinouts etc.  I don't expect
anyone to mail me detailed schematics or anything like that, just a
pointer to where to look for them.  (Though if someone *did* have data
sheets, I wouldn't say no to a quick fax :-) )

(fwiw, I used to do electronics as a hobby *years* ago - I once
built a dual-processor micro with dynamic ram, so don't be shy of
mailing me anything grossly technical; I've forgotten most of what
I knew in detail, but I remember enough to steer my uncle in the right
direction, though I won't be doing the actual circuit design myself)

Thanks for your time.  I hope this isn't considered too off-topic... (I
mean, I *could* have posted an incredibly interesting piece about the
Challenger disater instead, eh Eric? ;-))

G
PS Pointers to suitable usenet groups equally appreciated...

>Thanks for your time.  I hope this isn't considered too off-topic... (I
>mean, I *could* have posted an incredibly interesting piece about the
>Challenger disater instead, eh Eric? ;-))

Perfectly on-topic, Graham.

That said, I think that designing custom hardware for sound sampling
is a waste of time, given the abundance of multimedia cards that
already work.

The barrier to entry to solder up even the tiniest, simplest circuit
is enormous for most people.  Cypherpunks is not the Privacy League
for Hackers.  The solutions that we make should be to the greatest
extent available to all without special prerequisites.  That means
that hardware should be freely purchasable, since the resource of
money is more widely available that the resource of hardware skill.
It means that software should not require root for Unix machines, nor,
if possible, knowing how to operate a compiler.

While I applaud your enthusiasm, your effort toward getting usable
secure phones would be much betting spent writing device drivers for
various soundblaster-type cards.

Eric