Re: Poll preliminary results...

On Fri, 21 Aug 1998 15:43:40 -0700, Clay Cowgill <ClayC@diamondmm.com> wrote:

>> Only if you switch the voltage on a capacitor or something (similar to
>> the
>> Cinematronics design), if you try to draw the lines one step at a time
>> you run
>> into the same speed issues that have been discussed earlier.
>>
>Maybe. I don't need to do anything but draw pre-determined pictures of
>limited complexity though. I know Eric Smith had a limited function
>PIC->Vector tester working a couple years back. There's probably not
>enough time to bit-bang serial DAC data though...
>
>> I did figure out at one time that you could do a 1024 x 1024 vector
>> generator
>> using one of the 50mhz scenix(sp?) PIC clones if you used external
>> counters and
>> parallel DACs. I think you had something like 15 instructions to do
>> the main
>> draw loop.
>>
>For a full DDA probably. This would more likely be a series of loops
>that execute sequentially to draw the test patterns only... pseudo code
>time:
>
>(draw from upper left corner, to lower left corner, then to lower right
>corner...)
>
> counter <- +256
> y_count <- +128
> x_count <- -127
>left_side:
> y_count <- y_count -1
> output x_count, y_count
> counter <- counter -1
> if counter >0 goto left_side
>
> count <- +256
> x_count <- -127
> y_count <- -127
>bottom:
> x_count <- x_count +1
> counter <- counter -1
> if counter >0 goto bottom
>
>etc... Maybe have some nop's for timing. The drawing might not be
>exactly linear either, but enough to draw some test patterns.

This is what I was talking about with the capacitor thing. You can do the big
jumps (256 x 256) instead of the smaller ones (1024x1024) if you have some type
of lowpass filter to give the beam enough time to display a line between points.

This filter can be a R/C on the output of the op amp, it can be the slew rate of
the op-amp itself, maybe the speed of the yoke will keep you from being able to
jump to a new spot instantaneously, allowing the drawing of a line between the
two points.

It should be easy to hang a capacitor somewhere, or make a tweak here or there
to make a predetermined pattern look nice.

But if your going to do that, why even have DAC's? Just point to the four
corners in the right order and let the trace "charged" to the next position

I'll bet the X/Y testers are even simpler than the PIC thing you're talking
about.

With just a few shift registers and an R/C network you could probably create a
real simple pattern generator by simple turning off and on a resistor attached
to a capacitor and using the voltage on the capacitor to drive the X (or Y)
axis, as long as you timed everything right.

It would be even easier if you replaced the shift registers with a PIC, but
either way, chances are you won't need the DAC's, just good timing routines.

Didn't someone do something similar to this just using a Sound Card? I'll bet
if you setup the sample rate properly (which would set the lowpass filter
accordingly) you could write some simple software to test an X/Y monitor.
>
>> Since the Cine->WG board would basically be a full vector generator, a
>> nice way
>> to come up with a vector tester would be simply to drive the digital
>> inputs of
>> this board with a PIC processor.
>>
>True. I've got that ISA-Vector Video Card thingy too. (Neil pledged
>driver support. ;-)
>
>> >Think it needs three outputs for color? (or just one that
>> >you could switch from gun-to-gun? hard to do convergence that way
>> >though).
>>
>> Or three switches that allowed you to control each gun separately...
>>
>Yeah, I was just seeing if I could weasel out of the extra transistors
>and discretes. Actually, with surface mount 2n390x's it doesn't really
>take up much room to have full color...

Actually when I said switches, I meant "Switches" those toggle things ;^). I
was talking about the tester constantly generating a pattern for all three guns
(one B&W signal driving all three guns), and then having switch to turn off each
gun separately.

-Zonn

<><><><><><><><><><><><><><><><><><><><><><><><><><><><

 ------ ___ Member of A.A.C.S.:
 |---- | ( ) Association for Artistically
    / / ( () ) Challenged Signatures
   / / //\\ // (__)
  / ---/ // \\ //\\ // zonn @ zonn . com
 -------| // \\/
Received on Fri Aug 21 18:32:04 1998