On Mon, 27 Nov 2006, Les Cargill wrote:

Bret Ludwig wrote:
Arny Krueger wrote:

snip

You can find an audio interface that will outperform say a HP 334 for $30.
For $200 you're in the same league as some of the older, but not all that
old AP stuff.


Trying to use a PC as a general purpose bench instrument is like the
old race car guys that I used to hang out with. They would build a new
big block Chevy and a Turbo 400 behind it every couple of seasons. They
put in a dually one ton truck and pulled a trailer that would have been
just about right for an old single axle B Mack around for the season.
They got about five miles to the gallon under load too.

When I got older, I'd ask them why they didn't buy a real truck, you
know, air brakes, Fuller Roadranger, like a used Yellow or Roadway day
truck. Well, license and insurance cost too much and you needed a
"chauffeurs license" to drive it. (Those pre-CDL days!)

Well okay, at least put a diesel and an Allison in the pickup, why
don't you? Because we don't know how to work on them and you can't get
them in the junkyard for a hundred bucks.

Eventually they got tired of building "motors" (sic) for the tow truck
and not the race car and put a 3208 Cat or a turbo 4-53 and an Allison
or a Clark five speed in there. They then got like ten miles to the
galllon and the truck rusted out twenty years later and the engine and
trans still ran.

The PC does okay as a controller or as a dedicated production test box
with a buffered, isolated interface. But it is not like a scope or gen
or analyzer that sits on the bench.


*If* the thing under test is amenable to it, there's little
or no hope of improving on a PC soundcard

Are you talking about any PC _sound_card?

and Matlab as a combo. Might
need a breadboard to adapt the signals, but if it's in range,
it'll outrun just about anything for the money.

A PC _sound_card? Meant for _audio_ frequency ranges? Like single diget Hz
to 20-30 kHz? You think I'd rather have that than a decent DC to RF (X
mHz) oscilloscope 10 v/div down to 1-10 mv/div sensitivity? Time base
seconds/div to microseconds/div or less? And, can measure DC. Maybe if
you want to do some FFT or other DSP on an audio signal you can have the
soundcard. I'll pick the dedicated gear with specs that fit the ap.

You're assuming you can trust the test equipment. Sometimes,
you can't....

You mean you don't need to _assume_ the soundcard is working or you don't
need to worry about sw bugs or invalid process or tollerances or other
spec-dependent limitations? So, if the computer says "X" then it is
absolutely true, valid, straight from the horses mouth? No ands, ifs, or
buts? Do you know what the term "parasitic" means as it applies to chips?


--
Les Cargill