good oscilloscope for vector rescanning?

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johnnywoods
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good oscilloscope for vector rescanning?

Post by johnnywoods » Mon Feb 21, 2011 12:09 pm

inspired by Lars vector rescanning tests, I've started looking for a good oscilloscope for this purpose. The perfect one, as far as I know, would have a large bright screen, x, y, and z inputs, and a removable grid (or one that could be scratched off).
Anyone have suggestions for models that would fit the bill?

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Post by daverj » Mon Feb 21, 2011 3:05 pm

I built a raster manipulation device (my version of a Rutt-Etra) in the 80s using a Hameg oscilloscope. But that was back at a time when it was common to get scopes without the graticule etched right into the glass. These days I doubt if you can find a new scope without the etched glass. You might have to look for a 25-30 year old one.

Alternately you could modify a TV set to make something like the "Wobbulator" at the Experimental TV Center. It won't look the same as what Lars posted, but it does give some fun distorted raster shapes. Just not the deflection using video brightness that is characteristic of the Rutt-Etra look, and what Lars did on a scope.

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Post by lizlarsen » Mon Feb 21, 2011 11:32 pm

Yeah, Dave is correct -- I'm not sure if mine has the grid etched or not, but it probably does -- it's a Leader model. On the other hand,an XYZ scope isn't that hard to come by I don't think, and vector rescanning under a grid is better than no vector rescanning! :hihi:

There are arcade monitors out there sometimes... there's some schematics/parts numbers here:
http://www.mikesarcade.com/arcade/manuals.html

The Voltage Interface II module I'm working on is for scaling outgoing voltages and should be able to condition Visionary voltages for the right amplitudes to drive an arcade monitor. There's some specs on that for the VectorVGA here:
http://www.vectorvga.com/specifications.html

Dave, maybe you know, do you think there may be any luck to be had with the "Vector/Waveform" monitors typically used for broadcast test gear? Or do they not have Z inputs typically?

Vector rescanning is simply too useful/amazing/cool to give up on... I definitely look forward to doing some frame buffer type vector rescan programs, but its not going to be the same as a real display. In the modular environment it's just so powerful too, since you can have your colorizer and animation oscillators and matrix mixing all in the same environment. It would be quite a project, but I'd love to try to get some new vector monitors manufactured someday.

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Post by lizlarsen » Mon Feb 21, 2011 11:36 pm

Dave, maybe you also know this -- is it possible to replace the glass with something readily available, in the case of an etched plate? Or is there some sort of phosphor coating directly on it? I don't know enough about TVs/scopes, construction-wise.

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Post by daverj » Tue Feb 22, 2011 11:10 am

creatorlars wrote:Dave, maybe you know, do you think there may be any luck to be had with the "Vector/Waveform" monitors typically used for broadcast test gear? Or do they not have Z inputs typically?
A vectorscope and waveform monitor are specialized displays. They not only don't have a Z input, they don't have an X/Y mode. The vectorscope might look like it does, but that is somewhere internally. They are a color demodulator with the two demodulated outputs driving the X and Y. The Waveform monitor is a specialized oscilloscope with preset timebases.
creatorlars wrote:... is it possible to replace the glass with something readily available, in the case of an etched plate? Or is there some sort of phosphor coating directly on it? I don't know enough about TVs/scopes, construction-wise.
The problem is that they now etch the grid right onto the outside surface of the CRT tube itself. So there's no way to remove it. The older scopes had a piece of plastic laying on top of the tube with the grid on it. You simply took the face plate off and removed the plastic sheet from in front of the tube.

Some of the newer flat screen scopes don't have the grid etched on, but that doesn't gain you anything since those aren't true analog displays. They're just TV screens with digitized signals. They won't be any better than a digital vector to raster converter on a normal video monitor, which won't have the subtleties of a true analog vector CRT or scope tube.

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Post by lizlarsen » Tue Feb 22, 2011 12:01 pm

Cool, thanks for the notes!

I found a page with lots of replacement tubes (some with no lined graticule) here: http://www.sphere.bc.ca/test/crts.html

Of course fully redesigned driving circuitry would be time consuming for a one-off project!

Hmm, there has to be a manufacturer of OEM scope tubes still out there somewhere. Or a NOS lot.

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Old Tektronix

Post by offbyone » Tue Feb 22, 2011 2:26 pm

You might find an old Tektronix T-922 at a Ham fest or online.
They have a nice z-Axis input and the grat. comes off.

Here is a company that provides lots of info and does refurbs:
http://www.logwell.com/tech/oscilloscop ... T922R.html

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Post by smrl » Fri Feb 25, 2011 9:07 pm

I have an old heathkit scope IO-30 which has a removable graticule. No Z-axis in. I wonder if you could use an OTA in-line with the intensity control to hack together that functionality. Gotta dig for schematics now...

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Post by lizlarsen » Fri Feb 25, 2011 9:11 pm

I had a Heathkit scope with a removable graticule for a while too, but it went up in smoke! Let us know how your experiments go.

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Post by smrl » Fri Feb 25, 2011 9:17 pm

OO! there's a Z-axis in already behind a panel on the back.

I will definitely let you know how I get on with it.

Perhaps it's worth looking at how that was implemented on the heathkit to mod a different scope. Looks pretty simple.

http://www.eserviceinfo.com/download.php?fileid=39753

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Post by lizlarsen » Fri Feb 25, 2011 10:14 pm

I found a very simple circuit for generating H & V ramps -- this circuit definitely doesn't look ideal, but would get the job done if you don't have a video synth or the right gear to generate ramps...

http://www.electronixandmore.com/project/14.html

You can use a regular audio mixer's Left & Right busses to feed in X & Y, if you want to mix in various modulation with the ramp signals (still limited by bandwidth there of course.)

Here's another clip I recorded, this time colorizing the camera footage in a second pass. It got a little sloppy, but mainly I was trying to see if I could get the really bright spots to glow and bleed at a slightly different tint than the rest of the shot, and that worked nicely.
[video][/video]

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Post by BugBrand » Sat Feb 26, 2011 3:39 am

Lovely stuff!
And that simple circuit looks do-able to me - good for me to have a play with.

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Post by lizlarsen » Sat Feb 26, 2011 12:04 pm

You could also just do the LM1881 portion and use the output to sync two triangle oscillators if the sync circuit is stable enough. With triangle out you just need to set frequency to half a cycle, or ~7.5KHz for linerate, and some audio oscillators can sync that fast.

edit: Tom, your oscillator is XR2206 based right? That should work okay -- We were experimenting with those at first, they can be glitchy while being FM'ed but sync was pretty okay when running at a set frequency.

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Post by lionelfischer » Sun Apr 17, 2011 10:15 am

still learning: do you need three inputs, x y and z, for vector rescanning effects like this, what happens when you dont have the z axis, does the effect simply not work.

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Post by lizlarsen » Sun Apr 17, 2011 10:39 am

Hi Lionel. To do this style of rescanning, you need the Z input -- you'll just see a bright field with no image, since the Z-input is where the image is inserted. You can still create video art, lissajous figures, etc with an oscilloscope though, with only X & Y inputs.

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Post by daverj » Sun Apr 17, 2011 1:11 pm

You can create some great shapes without the Z axis. If you mix the video signal into the X and/or Y inputs, with the ramps, then you get the shape deflection that is shaped like the video signal and you get intensity changes as the scan lines spread or overlap.

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Post by lizlarsen » Sun Apr 17, 2011 11:30 pm

Yes, Dave's right. You can definitely still do some cool stuff with the video signal and ramps without a Z axis scope. It's just not going to represent as much of the original picture information as it would with the video controlling the brightness of the beam.

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Post by johnnywoods » Sun May 08, 2011 8:53 am

well, I took a chance on a wavetek 1901c X/Y Display Oscilloscope. It seemed perfect: big screen, X/Y/Z input, removable graticule, etc... It works fine when displaying typical waveforms, but when I tried vector rescanning, a few weird things happened. Hoping someone on here might know about this:

1) it only works if I swap the H and V ramps (so the image looks normal when I place the monitor on its side). When I patch the ramps in correctly, I get two skinny sine waves and that's it :despair:

2) With the H and V swapped, I get a recognizable image, but the horizontal access is doubled over itself. It's as if the video were folded in half lengthwise. No matter how I try to adjust the horizontal ramp, this is always the case. At best, I can get only one half of the image to appear cleanly.

3) The only control on the monitor other than typical X + Y offset/ gain controls is something called "vertical marker"... anyone know what that might be? I have a suspicion that might be the culprit.

It would be awesome to get this guy up and running properly. It could be the perfect display!

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Post by daverj » Sun May 08, 2011 1:05 pm

I can't find any technical info about the 1901C, such as bandwidth or sweep rates or input impedances.

It sounds like the horizontal ramp is being turned into a sine wave, which is why the scan folds over on itself. The sharp edge of the ramp should make the scope trace suddenly jump back to the start of the screen. But it sounds like the scope is either limited in frequency or the input is expecting a different impedance signal.

That "vertical marker" is something that is often used when using a marker sweep generator. It is a second input mixed with the vertical (Y) input. Normally it is fed a signal with a series of very thin spikes which show up as markers on the screen when doing a frequency sweep. It shouldn't be causing any issues with using it as an X/Y display.

A marker sweep generator is a piece of test equipment that puts out a high frequency oscillation that sweeps from a low frequency to a high one. At the same time it puts out a ramp wave (usually around 60Hz) in sync with the change in frequency. They often also put out a marker (or "PIP") signal which is a series of spikes at specific frequencies during the sweep. The oscillation is fed into a circuit being tested and the output of the circuit goes to the vertical deflection of the scope. If the circuit passes all frequencies then you see a flat, even shaded band on the scope. If the frequency falls off then the band gets thinner at that frequency. It's a way to see a wide range of frequencies all at once for a reasonable price at a time when spectrum analyzers cost $20k-$60k and most places couldn't afford them for production line testing.

So, if that's what this display is intended for, it's not surprising that the horizontal sweep is limited to low frequencies. The vertical axis though will be limited by whatever the target bandwidth of this deice is, which could be slow if designed for audio, or fast if designed for RF sweeps.

So it would be good to find specs for the device.

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Post by johnnywoods » Sun May 08, 2011 1:39 pm

Here's the only document I could find.
Thanks for the explanation! Very helpful :tu:
http://intranet.ntecusa.com/docs/WAV_10 ... 5_data.pdf

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Post by daverj » Sun May 08, 2011 3:31 pm

Yeah, I saw that too. But it's specs are mostly about the over all system and it's not clear what those devices are doing to create the actual scope signals.

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Post by Veqtor » Mon May 16, 2011 1:30 pm

My oscilloscope seems far too slow to do anything interesting... :waah:

Just going to have to wait for the lzx vector>raster module...

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Post by lizlarsen » Mon May 16, 2011 2:56 pm

My oscilloscope seems far too slow to do anything interesting...
Do you mind telling a bit more about your setup/technique and the device you're using? :) Maybe we can help you get it working. What scope is it?

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Post by Veqtor » Tue May 17, 2011 8:02 am

I'm just doing quite complex shapes using X, Y and Z inputs, what makes the scope go nuts is when I have these really fast saw-waves superimposed on the general shape to create kind of "block" or thick portions of the shape, at low frequencies they work great but then I get his flickering, if I go into higher frequencies all the details disappear.

I'm just using monophonic rca to minijack cables that go into rca bnc connectors, perhaps I need some kind of resistor to change the impedance?

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Post by Veqtor » Tue May 17, 2011 9:57 am

Wow, I retried it with a lot more luck, this time I got some crazy old school gfx by having an afg generate the field and z3000 the lines and then I crossmodulated the two w. a doepfer a-189-1 vc bit modifier.

I think digital effects could be really useful in video processing!

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