Bringing vector graphics displays back to life - Page 2

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it

I think a 68000 is overkill. I've seen the kind of thing you describe
implemented in discrete logic with EPROMs, an address counter, and
R-2R ladders as the DACs. The R-2Rs are on the EPROM data buses, the
address counter is on their address buses, there is a single timebase
(a 555 rigged as astable multivibrator) clocking the address counter.
The X-Y inputs of the scope are connected to the R-2R outputs. The
intensity control isn't necessary (for a simple circuit); you just
trace out the shape you want repeatedly (as long as you can live with
everything being joined up).

In fact, the circuit I saw is part of a funny story: It was built by
two physics students in first year at the University of Melbourne
(Australia) in 1990. They were radio hams, and generally electronics
mavens, and first year "introduction to the oscilloscope" physics lab
was a waste of time for them. So they built this circuit and concealed
it in a hollowed-out pineapple. They ran the X-Y and GND wires up the
undersides of the pineapple leaves, and reassembled the fruit. They
clipped the scope probes to the leaves (carefully concealing the wires
underneath) and called the teacher over to say "Look sir, this
pineapple is doing strange things".

I forget exactly what the pineapple was "thinking" but I recall the
first screen had a vector image of a pineapple with a thought bubble
coming out of it. The next few had text, something like "THEY DO NOT
SUSPECT", "WE WILL SOON TAKE OVER", etc.

Note that their circuit was a *TAD* more complex than I've described.
Each "frame" was refreshed at the full timebase rate from the LS bits
of the counter, then there was a gap in the counter->address line
mapping, so that each frame would stay onscreen for [n] clocks.

Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it
or
could
8051

I think a 68000 is not overkill if it has to dynamically build a vector list
from character input which is coming from serial port.  This was the next
'step' in my idea.

Quoted text here. Click to load it



Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it

Hrmf... Actually, no, this doesn't change my statement any. I still
think it's overkill. The horsepower required to transmute "64,64" to
0x00000040, 0x00000040 is negligible. The speed bottleneck in this
system is likely to be the serial interface (if by "serial" you mean
"RS232"). I'd say this is all well within the capabilities of a
reasonably frisky 8-bit microcontroller.

BTW, why 68000? It's relatively complex to interface with, and (IMHO)
a moribund architecture. Why not a cheap ARM like Philips LPC21xx? It
has all the ROM and RAM you need on-chip, and it's in a handy QFP
package that's easy to prototype.

Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it
list
next

It is a simple matter of availability and of knowledge.  My school has an
army of 68k SBC's ready to go and complete with digital I/O ports and a
sub-board for inserting external IC's.  Contrary to zero LPC's.  Besides I
learned to program assembly and C on these machines.  But if some
architecture is *far* more suitable for the task I originally posted, I am
willing to adopt it.



Re: Bringing vector graphics displays back to life
Is this what you talking about?

http://www.cathodecorner.com /

scroll down a little bit...



Seems like the guy pulled it off with a microcontroller and a few fast
DACs.  It's a project that's cool enought that I would try to
duplicate it if I had the time.

-Jim


Quoted text here. Click to load it

Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it

Cool! An another cool thing is that the tube looks very much like
the one I recently bought. It was (is?) for sale as a 'decorative
paperweight' from Conrad (dutch/german mailorder). Cost only a few
(7?) euros and turned out to be a new CRT in box.

Pitty the page does not give more info on how the tube is controlled,
any info on that anywhere?


--
Stef

"In order to make an apple pie from scratch, you must first create the
We've slightly trimmed the long signature. Click to see the full one.
Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it

Sounds extremely dangerous to the ignorant.  What if that
'paperweight' falls off the table and implodes?  It would be quite
easy to lose your eyesight.

--
Chuck F ( snipped-for-privacy@yahoo.com) ( snipped-for-privacy@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
We've slightly trimmed the long signature. Click to see the full one.
Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it
Never thought about that. And I personally would not leave it out
of it's foam-packed box until I actually use it (as CRT), but
someone could.

Just checked to be sure: It has not been made useless, so vacuum
must still be intact. It is a 3", 7" long, tube. No labels
'danger' or 'fragile'.

Conrad is an electronics mail order company so it is not very likely
that 'normal' people will order there. It was advertized in a
special with old stock items, not in the normal catalog. Not sure
if you can still order it though.

Why it was labled 'paperweight', I don't know. Thinking about it,
the words 'paperweight' and 'fragile' do not go together very well.


--
Stef

"In order to make an apple pie from scratch, you must first create the
We've slightly trimmed the long signature. Click to see the full one.
Re: Bringing vector graphics displays back to life
U snipped-for-privacy@umassd.edu (Mood) writes:
Quoted text here. Click to load it

I've built one.  His design does not need fast DACs.

Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it

For small strokes, based on an xy location, one needs two
integrators and mixers to combine the x, xdelta, and y, ydelta
positions.  You also want z axis (blanking) control.  It is then
easy to create a 7 segment display (which needs eight, one of
which is alway blanked) which returns to the point of origin.  I
have done this to write numbers etc. on CRT displays.  More
complex patterns can be generated with no more hardware.

By mixing the ydelta into the x display, you can create the degree
of slant required.  One more resistor.

Operation is a matter of:

   Select x,y in the main registers (d to a or any other way)
   launch a fixed pattern on the xdelta, ydelta lines.  The x and
y deltas may be plus, zero, or minus a standard voltage.
   Simultaneously launch a digital pattern on the z line, which
describes the segments of the pattern unblanked.

Repeat as desired.

Having the stroke generators return to the point of origin is
necessary to avoid accumulating errors in the integrators.

--
Chuck F ( snipped-for-privacy@yahoo.com) ( snipped-for-privacy@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
We've slightly trimmed the long signature. Click to see the full one.
Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it

Yeha, that was admittedly a guess.  That would be my solution, being a
software puke and all.

On closer inspection of his equipment, I noticed an abundance of small
IC's (I assume op-amps) and trim pots labeled 'SIN' 'COS' 'XPOS'
'YPOS'.  Maybe alot of the shape generation is analog, while
postioning of shapes is handled by a small micro?

I'd like to buy a kit, but the price is steep, though I defintily
think it's a fair price considering the work put into designing
something like that.

-Jim

Re: Bringing vector graphics displays back to life
Quoted text here. Click to load it
snip

snip
 >

have a look at this:
http://www.analog.com/Analog_Root/static/library/dspManuals/pdf/Volume1/Chapter_9.pdf

it's for a DSP but it should give an idea on how it could be done...

-Lasse


Re: Bringing vector graphics displays back to life

Quoted text here. Click to load it
[snip]
Quoted text here. Click to load it
can
I
most
[snip]
Quoted text here. Click to load it

How about taking the stereo outputs of a sound card and using the left
channel for X and the right channel for Y? The left channel then becomes
a list of X coordinates and the right channel a list of matching Y
coordinates.
Create a wav file, then use your PC to play it over and over. That should
work for static images.

If you want to do something more complicated, you'll have to use a double
buffering scheme -- while the sound card "plays" one image, build the next,
then switch buffers. The nice thing about this is that you can let sound
card
display the image via DMA from memory while your CPU is generating
the next image.

I'm not sure what you would do about intensity except to suggest maybe
using a second sound card or one with more outputs. Good luck.

Scot Allen




Site Timeline