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From: GiveMeL on 10 Jun 2010 17:57
I was wondering if anybody has tried using a cheap video capture card
as a (cheap) scope?

Any pointers?

TIA!

P.


From: hamilton on 10 Jun 2010 18:01
On 6/10/2010 3:57 PM, GiveMeL wrote:
> I was wondering if anybody has tried using a cheap video capture card
> as a (cheap) scope?
>
> Any pointers?
>
> TIA!
>
> P.
>
>
A video card looks for vertical and horizontal sync pulses to sync the
capture memory.

Sound like cheap is out the window.

hamilton

From: GiveMeL on 10 Jun 2010 18:14
There is no way to bypass (part of the) input circuitry and feed a
voltage directly to the adc?



From: Jan Panteltje on 10 Jun 2010 19:02
On a sunny day (Thu, 10 Jun 2010 14:57:16 -0700 (PDT)) it happened GiveMeL
<pete.berglund(a)gmail.com> wrote in
<207a80e1-b025-4cc0-ac5d-96236fac178d(a)k39g2000yqb.googlegroups.com>:

>I was wondering if anybody has tried using a cheap video capture card
>as a (cheap) scope?

Not wit ha video card, but many years ago (> 35 I think),
I devised a very clever circuit to use normal video display as a scope,
so that should also work via your frame grabber, worked fine for me.
I will try to explain how to do that:

Some who are familiar with old trick effect generator may quickly see this.

Anyways, start with generating a white dot on the screen.

You create a H frequency ramp, and a V frequency ramp, and a composite sync pulse first.

Now you take 2 window comparators, (window comparators are circuits that give a logical 1 if the signal is in a given range,
you can make one out of two normal comparators and an AND gate), anyways you feed
the H ramp into one widow comparator and the V ramp into the other.
On the other input of the first window comparators you put your vertical scope input,
and on the other input of the other one your horizontal timebase.
Then you AND the output of the 2 window comparators together and sum that with the
composite sync to make a white pulse.
With all signals in midrange you get a horizontal white line.
The spot diameter is set by the window aperture.
It works only slowly.
Nice for a heart monitor or such.
IIRC I could drop the horizontal timebase and use one window comparator,
then it would scan at H rate, I had a 560 kHz signal displayed on a normal color set
that way, used fast transistors to make the comparators and diode AND gates.
Was for sure 5 MHz bandwidth :-)
From: hamilton on 10 Jun 2010 19:24
On 6/10/2010 4:14 PM, GiveMeL wrote:
> There is no way to bypass (part of the) input circuitry and feed a
> voltage directly to the adc?
>
>
>

By this statement you have no idea of what can or can not be done.

good luck

hamilton
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