Re: vectorbeam hardware

Look at this board's detailed (not general) specs, etc... It should settle
fine for what you are doing

http://www.computerboards.com/cbicatalog/cbiproduct.asp?dept%5Fid=231&pf%5Fi
d=666

2 channels of D-A and 48 bits of digital output which, with some resistors,
and an op amp can do the beams.
Or, you can take the easy way out and use an 8 output D-A board for $$
It's getting expensive.

James

----- Original Message -----
From: Adam Wiggins <adam@angel.com>
To: <vectorlist@lists.cc.utexas.edu>
Sent: Friday, November 26, 1999 6:02 AM
Subject: Re: vectorbeam hardware

> On Thu, 25 Nov 1999, Rodger Boots wrote:
> > The Vectorbeam/Cinimatronics used the DACs to charge a capacitor to the
> > starting point and then had the DACs charge the capacitor to a finishing
> > point that (through a resistor) that was WAY past where they wanted to
go.
> > Then they only used a small part of the charging of the capacitor as
their
> > line. This gave them a relatively linear line out of an exponential
> > charging curve. A timer determined how long to generate the line.
>
> Ah ha! This is the information I was looking for.
>
> > Doing it your way you'll need a software version of a rate multiplier.
> > Initialize the DACs to the starting point. For example, let's say you
then
> > want to draw a line that's moving to a finishing point 50 steps in the X
> > direction and 30 steps in the Y direction, take the larger number (50)
and
> > make a for-next loop that changes X from the starting to the ending
value.
> > Inside that loop you will change X by 1 for each iteration and Y by
30/50
> > (.6). This will create your smooth line. Just don't go faster than the
> > monitor can move and you'll be OK. NONE of this needs to be floating
> > point math.
>
> In other words, draw a line the exact same way that you would on a raster
> monitor. :)
>
> Yes, that was the first thing I thought of, and I think I mentioned that
> in my first post (that Zonn replied to). My problem is that I get a
series
> of very close together bright points, which of course is not what I want.
> Since I refuse to believe that a 450mHz processor is not able to compute
> a few thousand points per second, I determined that the slowdown is
happening
> at the level of my analog output card. Checking the documentation, it
lists
> 70 microseconds as the settling time of each DAC channel. Glancing at the
> specs for the AM6012 used in Atari vector games, it reports a latency of
> 250 *nano*seconds. Quite a difference. So I must assume that the board
> I'm using is too slow.
>
> So that leads me to a whole new question: what's the best way to get an
> analog output from a PC that is fast enough to control a vector monitor
> beam accurately? Is it the ISA bus of the PC that is not fast enough?
> Would a PCI board do the trick? (The best I've seen in premade analog
output
> boards is 2us, which is still larger than 250ns.) I'd really like to be
> able to just buy a couple of speedy 16 bit DACs and slap them onto the
back
> of my PC, but of course there's no convenient high-speed output. Serial
> and parallel are probably too slow, and USB is probably too complicated
for
> me to wire up.
>
> Any thoughts? Right offhand it seems that the best option would be to
> build a PCI board that just has a couple of DACs on it, but my knowledge
> of electronics and the PCI bus are both minimal enough that I'm not even
> sure how complicated of an endevour this would be, or even if I could
> achieve speeds fast enough to draw nice smooth vector lines.
>
> Thanks again!
> Adam
>
>
Received on Fri Nov 26 07:27:18 1999