Re: Anybody with an oscilloscope as an Apple II display?

[Charlie Springer <RAM@regnirps.com>]

On Wed, 26 Mar 2008 16:58:09 -0700, Michael J. Mahon wrote
(in article 
<bf9c4e5d-9c84-447d-aa73-f97f9db0769d@8g2000hse.googlegroups.com>):

> On Mar 25, 9:51�am, heuser.mar...@freenet.de wrote:
>> Something on the line of this 
>> here:http://www.youtube.com/watch?v=s1eNjUgaB-g
>> 
>> Maybe not as detailed but is it feasible at all?
> 
> You need dual D/A's to generate such a display.  The speed with which
> the outputs
> can be changed--which soon becomes the speed with which the outputs
> can be
> computed, is what limits the complexity of the display.
> 
> Although it is possible (with appropriate analog post-processing) to
> generate
> a straight line segment by sending just the new end point (a vector
> display),
> in practice one would send several intermediate points so that simple
> low-
> pass filtering would produce the desired trajectory.
> 
> It's actually an older form of computer graphical output, since it
> preceded
> raster graphics by a decade or more.
> 
> -michael

Some scopes have TV inputs and use a built in vertical and horizontal ramp 
generator with the video driving the Z axis, usually a 20 volt signal.

In the late 70's I tried a couple dozen circuits to make a good analog vector 
display using D/A from an AIM-65 (same speed and processor as A II) and an 
X-Y scope. I couldn't handle very many vectors in real-time and would need 8 
an MHz Zip or the like to make it worthwhile. memory isn't a problem for a 
vector display since any line is defined by two (x,y) pairs. If you use 8 bit 
converters (256x256 display) you can go pretty fast. I used 12 bits and had 
to do twice as many LDA STA pairs per vector.

The images on the scopes could be simpler than raster. The words were made 
wavy by riding a sine wave and if you use (X,Y,Z) lists where Z is an on/off 
bit, and sort them -- well, the scope is probably fast enough that sorting 
won't matter -- just cycle though the list turning the dots on and off as 
fast as you can. You obviously don't need enough memory for the full raster.

Oh, the old analog stuff used integrators to get nice straight lines and an 
analog multiplier to calculate the brightness, depending on the speed each 
vector was drawn across the screen. I was looking for an integrator circuit 
with what I called automatic endpoint matching to make a better display for 
the Battlezone arcade machine, which approximated the vectors with the first 
part of a cap charging IIRC. Raster displays overtook the effort. I still 
prefer the look of a vector display for some applications. See the navigation 
displays in 2001 A Space Odessey.

-- Charlie Springer