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Laser Vector Display

EricBall

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Earlier this month the family and I spent a week camping at (nee Six Flags) Darien Lake - riding roller coasters & other rides plus roasting marshmallows & drinking beer. Every night DL has a laser & fireworks show set to music. (Unfortunately the same one every night.) The laser show part of the show in particular was particularly impressive and would have made Pink Floyd (from 40 years ago) green with envy - complex animated scenes in full color. (Probably restricted more by the creation tools and software capabilities than the actual hardware.)

But seeing what a modern laser projector is capable of got me to thinking - could one be used as a replacement for a vector monitor (e.g. Asteroids and Tempest)?

But then I suspect was others probably had had the same thought - and there's probably a big reason why I've never heard of a laser version of Tempest. Of course, last week's insurmountable problem might be this week's trivial solution. So I started with a little investigation.

To make a long story short, the limiting factor is moving the beam. A vector monitor uses electromagnets, while a laser display uses mirrors - typically using a variation of a "mirror galvanometer" or galvo. People have made their own galvos using the voice coil actuator from a hard disk (which is what moves the heads across the disk). But electromagnets can change the position of the beam from one side of the monitor to the other in 100-300 microseconds, whereas it requires 10-20 milliseconds to move the head across the entire disk. That's 100 times slower and a bigger challenge than I think can be easily overcome.



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It looks like they have a lot of flicker, so aren't simply driving the laser with the raw vector outputs.

 

Yep http://web.archive.org/web/20040401223651/http://games.lasers.org/pressrelease.shtml

 

 

Because of the fundamental differences between a cathode-ray tube’s high-speed drive yokes (which trace the electron beam across the phosphors of the monitor) and relatively low-speed mechanical laser scanners (used to move two small, millimeter-sized mirrors which deflect the laser beam’s direction), the native CRT signals generated by traditional game hardware are completely unusable for laser projection.

Part of the fundamental problem of game display in laser is simply inherent in the speed at which the vectors are output by the game. An electron beam, having no real mass, can sweep at (comparatively) an almost ‘infinite’ speed, whereas mechanical scanners need to deal with the physical aspects of mass, inertia, and acceleration. These three factors greatly limit the speed and accuracy at which the mirror can move. Where a vector monitor can handle simply the first and last points on a straight line, a mechanical scanner needs a trail of points along the straight line in order to faithfully and accurately reproduce that line. Where a vector monitor can change direction instantaneously (again, because the electron beam has no real mass to speak of) a mechanical scanner must brake, stop, and take off into a new direction to reproduce the angle-change correctly. These are only a few of the conversions and optimizations performed in real-time by LaserMAME™, all of which are necessary for successful image conversion.

 

Not to dismiss what they did - the display looks good. But the galvos are definitely the limiting factor.

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Cost aside, wonder how well it would work if they could divvy the output amongst multiple lasers.

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Cost aside, wonder how well it would work if they could divvy the output amongst multiple lasers.

 

How much time, money & effort are you willing to spend? The first step would be to somehow divide up the display into vector sequences. Both the Vectrex and Atari games after Asteroids (Deluxe) use analog vector generators. So each vector sequence would start with a "return to center" which could be used as a starting point. (The vector sequence is then drawn as a series of slope + speed over time at intensity or off.) The vector sequence would need to be slowed down for the laser projector, tweaked to account for momentum and the output buffered.

 

Then you'd need a bunch of laser projectors. You'd want to make them as physically small as possible so they can be placed close together rather than trying to create some kind of "multi angle beam combiner". As long as the distance between the outputs is small relative to the final display the parallax shouldn't be too noticeable.

 

However, to make any significant difference you'd need a lot of laser projectors (tens at least). And hopefully each vector sequence could be drawn quickly enough to match the game's internal refresh rate.

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I'm not willing, just speculating on a way to speed up output.

 

Physically small and close together aren't needed - my Mitsubishi HDTV uses three 7" CRT tubes with quite a bit of space between each one (probably so the magnetic fields for the tubes don't interfere with each other).

Say you used 9 laser projectors lined up like this:

1  2  3
4  5  6
7  8  9

just use an offset for center:

1 = (1,1)

2 = (0,1)

3 = (-1,1)

4 = (1,0)

5 = (0,0)

6 = (-1,0)

7 = (1,-1)

8 = (0,-1)

9 = (-1,-1)

 

Would need a way to calibrate the offset, but that shouldn't be too difficult - have laser 5 draw the corners of a box, have laser 1 draw the sides of the box, adjust the values for laser 1. Repeat for 2-4 then 6-9.

 

If that wasn't enough then do something like the advanced convergence my Mitsubishi HDTV has. Looks just like guy's set, though my menus to get to the convergence screen look different.

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A couple more videos about using lasers to emulate vector displays:

 

Custom code to duplicate Asteroids - points out that galvos are slower and how momentum makes corners round unless the code includes the proper de-acceleration

 

On a commercial laser projector, which now includes homages to various vector games

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