Maybe un-useful, but one I have thought of often.  Here's my thinking:
Forget trying to get high speed analog signals into your PC.  Have an
external box that captures the waveform, scales it, isolates it from your
precious PC's ground and power supply, and also scales it in the time
dinemsion, and wraps a nice ground plane around it..  Jam a bitstream into
whatever port is easy - RS232, parrallel, or USB (if it were a commercial
product USB would be the way to go) and use the PC's megabytes of memory for
the digital storage, use the PC's powqerful graphics for the display, and
use the brain for things like displaying the RMS value as a digital
voltmeter, counting the frequency, counting the pulse width, all the things
that take a lot of squinting or guessing on an old analog scope.  At least 4
channels, plus a few logic channels like an HP mixed signal scope.

Now if we are going to measure signals in the megahertz range, we are out of
the PIC's league.  How do TEK and the other big boys achieve A/D conversion
in a 100 mHz scope?

keep in mind this is just an interesting mental excercise - I'm not planning
on building this anytime soon.  Besides, they already make them.

--Lawrence


> Probably un-useful thought - a modern PC would make an interesting high
> speed scope using eg a Sigma Delta A2D if you could burrow under the
> operating system and timers etc. You might be able to get many 10's of MHz
> of analog bandwidth using a now entry level Celeron/AMD/xxx 850/1000 MHz
cpu
> and a parallel port.
>
>
>
>
>         Russell McMahon
>

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