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light gun compatibility

 
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moonub




Joined: 13 Mar 2021
Posts: 1
Location: Redwood City, California


PostLink    Posted: Tue Mar 16, 2021 4:00 pm    Post subject: light gun compatibility Reply with quote


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Hello everyone

I'm currently obsessed with trying to play some old gun light gun video games using a CRT projector. I was hoping the collective here could advise me on a model that might work? I've been running all over this site, and a lot of other internet forums on CRT TVs and retro gaming. I think I have a good idea what I need but will definitely benefit from an expert's opinion here.

I don't know if you are familiar with this tech at all, but the original technology for these light gun video games was entirely dependent on CRTs. As TVs have switched over to LCD and Plasma, totally different technology was needed to make these games play (e.g. mostly using infrared emitters and receivers).

In case you are not familiar with how this tech works, here is a brief description copied from https://electronics.howstuffworks.com/question273.htm

"Lots of home video games and arcade games use some sort of gun as an input device. You point the gun at the screen and pull the trigger, and if you hit the target on the screen, the target explodes.

To create this effect, the gun contains a photodiode (or a phototransistor) in the barrel. The photodiode is able to sense light coming from the screen. The gun also contains a trigger switch. The output of the photodiode and the switch are fed to the computer controlling the game.

At the same time, the computer is getting signals from the screen driver electronics. The screen driver electronics send pulses to the computer at the start of the horizontal and vertical retrace signals, so the computer knows where on the screen the electron beam is located during each frame.

When the user pulls the trigger, the computer blanks the screen and then paints the entire screen white. It takes time for the electron beam to trace the entire screen while painting it white. By comparing the signal coming from the photodiode with the horizontal and vertical retrace signals, the computer can detect where the electron beam is on the screen when the photodiode first senses its light. The computer counts the number of microseconds that pass between the time the horizontal and vertical retrace signals start and the time the photodiode first senses light. The number of microseconds tells the computer exactly where on the screen the gun is pointing. If the calculated position and the position of the target match, the computer scores a hit."

It's actually a pretty amazing method.

I've been researching using a CRT projector with these light gun games, and it is possible. Here's someone demonstrating on YouTube https://www.youtube.com/watch?v=CxbrxXPBigk&ab_channel=beaumotplage
And from 5 minutes, 14 seconds in this video: https://www.youtube.com/watch?v=faLsQ1DnRX8&ab_channel=beaumotplage

From what I understand, not all projectors will work. The light guns include a diode that struggles to keep up with fast refresh rates. 100Mhz CRT TVs won't work. So it's possible that projectors running 100MHz will have the same problem.

It also seems that HD CRT TVs are no-go. At higher resolutions (720p, 1080i, 1080p) the scanlines become hard to differentiate and these guns struggle.

There's a lot less guidance on internet forums about using CRT projectors with these guns, but it sounds like CRT projectors which are very high resolution, or which include line doublers or anything which upscales the signal can stop the guns from working. I think the underlying cause in these cases is either that the guns are unable to read the scanlines on the screen, or there is some lag introduced between the computer and the on screen image which prevents the program lining everything up. Lastly, these guns work by using a light receiving diode in each gun, so the brighter the screen the more likely they are to function properly.

I know there's a lot in my post here. Perhaps you are already familiar with all this, and if not, I hope you are intrigued!

Based on my research, I think I'm looking for a projector that has no upscaling / line doubling, nothing that introduces lag in the circuit, opportunity to run it at lower frequencies, and ability to run in lower resolutions (640x480i). But ideally also very bright. And in a perfect world some easy connections to link to "recent" video input formats: composite, component, or HDMI (though I am expecting I'll be adding a bunch of adapters, mostly likely).

Again, hope I have you intrigued and that you might have some good ideas that might fit the bill.

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Currently obsessed with light guns and retro gaming, and making it all possible on big screens.
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garyfritz




Joined: 08 Apr 2006
Posts: 12024
Location: Fort Collins, CO


PostLink    Posted: Tue Mar 16, 2021 4:48 pm    Post subject: Reply with quote

Maybe Jeremy (AnalogRocks) or Zebra can help you:

http://www.curtpalme.com/forum/viewtopic.php?p=494187&highlight=light+gun#494187
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wanderer




Joined: 11 Jan 2015
Posts: 63



PostLink    Posted: Tue Mar 16, 2021 5:29 pm    Post subject: Reply with quote

You should be able to upscale something 480i to 480p and feed that to basically any CRT projector and it will likely work with a light gun. Speed of the i to p processing is important, but here is a good video showing the old NES doing 480i > 480p and onto a Cine9 playing duck hunt: https://youtu.be/hcFlXATEiS8

I used to run House of the Dead 2 from my Dreamcast using the VGA output adapter at native 480p and played that with dual light guns on an NEC 9pg Xtra projecting onto the wall with about a 90" image. This was back in 2001 though, although I still have the Dreamcast so this might be a retro project in the future. It was pretty cool to do back then!
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kal
Forum Administrator



Joined: 06 Mar 2006
Posts: 17850
Location: Ottawa, Canada

TV/Projector: JVC DLA-NZ7


PostLink    Posted: Wed Mar 17, 2021 12:37 pm    Post subject: Re: light gun compatibility Reply with quote

Welcome to the forum!

I'm certainly no light gun expert, but used to own one of the earliest pong-type game systems back in the 1980s that included a light gun. Wink I've owned many CRT projectors and understand the electronics/functionality behind CRT projectors.

moonub wrote:
From what I understand, not all projectors will work. The light guns include a diode that struggles to keep up with fast refresh rates. 100Mhz CRT TVs won't work. So it's possible that projectors running 100MHz will have the same problem.

100Mhz is the projector's bandwidth I would presume. Nothing directly to do with refresh rate which will usually be around 60Hz (or 59.94 to be exact). A 100Mhz bandwidth CRT projector can display a 480i signal as can a 10Mhz bandwidth CRT projector. Check out this page I put together years ago that explains terminology: http://www.curtpalme.com/Projector_Rankings.shtm

moonub wrote:
It also seems that HD CRT TVs are no-go. At higher resolutions (720p, 1080i, 1080p) the scanlines become hard to differentiate and these guns struggle.

The light gun just reads light from what I understand. It doesn't care and can't know what resolution the square on the screen is. I really doubt a light gun has to try and 'see' scanlines. That doesn't make any sense to me. If the gun has a simple light receiving diode it has no concept or understanding of what the picture is that is producing the light. It's just reading light level. Otherwise a CRT display that is not perfectly focused or slightly off in the corners where scanlines touch/blur wouldn't work at all. A light gun only measures light. For a light gun to "see" scan lines it would require some sort of image capture device, like a camera, with multiple sensors in order to "paint" the picture to see scanlines or similar. Maybe later more advanced light guns did were like that (basically digital cameras behind a zoom lens or similar) but I doubt it.

moonub wrote:
There's a lot less guidance on internet forums about using CRT projectors with these guns, but it sounds like CRT projectors which are very high resolution, or which include line doublers or anything which upscales the signal can stop the guns from working.

The earliest CRT displays (and CRT projectors) were 480i. Later models could scan and lock on to higher frequencies. Again, how well you saw scan lines (or not) was dependant on the type of CRT technology used (EM vs ES focus, tube size, etc). CRT displays have no native resolution. Very few CRT displays had built in doublers or similar. A few did, but they basically sucked. Everyone used external scalers or HTPCs.

Quote:
Based on my research, I think I'm looking for a projector that has no upscaling / line doubling, nothing that introduces lag in the circuit, opportunity to run it at lower frequencies, and ability to run in lower resolutions (640x480i).

That's pretty much any CRT projector that's ever been built.

Quote:
But ideally also very bright.

That's all relative. The bigger the tubes, the smaller the screen, the brighter it will be. A higher gain screen will also increase the reflected light.

Good luck!

Kal

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jbltecnicspro




Joined: 23 Apr 2016
Posts: 512



PostLink    Posted: Tue Mar 23, 2021 4:41 pm    Post subject: Re: light gun compatibility Reply with quote

kal wrote:
Welcome to the forum!
100Mhz is the projector's bandwidth I would presume. Nothing directly to do with refresh rate which will usually be around 60Hz (or 59.94 to be exact). A 100Mhz bandwidth CRT projector can display a 480i signal as can a 10Mhz bandwidth CRT projector. Check out this page I put together years ago that explains terminology: http://www.curtpalme.com/Projector_Rankings.shtm


I think he misspoke and what he means is 100hz refresh TV's. I presume from Europe. And he would be correct. 100hz TV's are incompatible with light guns for the reasons below.

kal wrote:

The light gun just reads light from what I understand. It doesn't care and can't know what resolution the square on the screen is. I really doubt a light gun has to try and 'see' scanlines. That doesn't make any sense to me. If the gun has a simple light receiving diode it has no concept or understanding of what the picture is that is producing the light. It's just reading light level. Otherwise a CRT display that is not perfectly focused or slightly off in the corners where scanlines touch/blur wouldn't work at all. A light gun only measures light. For a light gun to "see" scan lines it would require some sort of image capture device, like a camera, with multiple sensors in order to "paint" the picture to see scanlines or similar. Maybe later more advanced light guns did were like that (basically digital cameras behind a zoom lens or similar) but I doubt it.
Kal


Most light guns look for a light square displayed by the device to know whether or not you hit the target. The problem with HD sets is that most are not natively running 480i/240p and thus introduce lag in scaling up to their native resolution. That few milliseconds matters to a light gun which is precisely looking for the square at a precise time. So you're right. It's just that the light gun cannot see the light because it's not looking long enough, if that makes sense. By the time it looks for the spot on the TV and registers whether or not it's been hit, the TV hasn't yet displayed the square.

So for light guns, I'd say any CRT projector that natively handles 480i/240p without scaling (like you said, pretty much all of the ones you can find) should work just fine.
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