Light Guns and Speccy

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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retro_collector
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Light Guns and Speccy

Post by retro_collector »

I am thinking of getting a light gun for the spectrum.

So these questions:

Any SPectrums with Composite or do I need to do the mod?

Which spectrum is the best for composite and light gun?

Are there enough light gun games to make it worth while?

Please let me know your opinions

Thanks

Bill
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ZXDunny
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Re: Light Guns and Speccy

Post by ZXDunny »

You absolutely, definitely need an old CRT TV to play on. LCD will not work. I'm not sure if composite will affect it; I suspect not.
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1024MAK
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Re: Light Guns and Speccy

Post by 1024MAK »

UHF / Composite Video / RGB Video - does not matter. But results may be better if using composite or RGB.

The 16K/48K/+ only have UHF TV outputs as standard, but can be modified to output composite video (may not work with all TVs).

128K toastrack: RGB (TTL level) and composite video both available from the RGB/video/monitor socket.

+2 (grey): RGB (TTL level) and composite video both available from the RGB/video/monitor socket (assuming the default configuration is wired up on the PCB). But some units require a modification to correct a manufacturing problem.

+2A, +2B, +3: Only RGB (TTL level) is available from the RGB/video/monitor socket. Composite video is not available. It can be added, but requires extra circuitry.

Note: the video output using any of the above connections may not work with all TVs, as there are limitations between the output signals and the signals that modern TVs expect. Older CRT TVs, being analogue are much more forgiving in this respect.

No ZX Spectrum model has any specific hardware support for a light gun or light pen. Because of this, performance is nowhere near as good as computers where there is built-in hardware support and a CRT display is used.

Some light guns were produced for the 128K models, they connect to the RS232 or Aux port (sorry, can’t remember which).

Before then, light guns either used a bespoke interface, or connected to a compatible joystick interface (with the 9 way D-connector wired to the Atari standard).

Mark
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retro_collector
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Re: Light Guns and Speccy

Post by retro_collector »

Thanks Mark and ZXdunny,

I have 2 CRTS, one is VGA and the other accepts Composite or Svideo.

I have my eye on Cheetah Defender Light Gun. I have a +3 speccy but as we all know there is no composite.

How many games are there for this light gun?

Thanks
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Re: Light Guns and Speccy

Post by Alessandro »

retro_collector wrote: Mon Sep 16, 2019 3:43 pm How many games are there for this light gun?
This is a compilation which came with the Cheetah light gun: https://spectrumcomputing.co.uk/index.p ... 6&id=11242

You could also try the compilation which was bundled with models sold with the Sinclair light gun: https://spectrumcomputing.co.uk/index.p ... 6&id=11353

With the Magnum Light Phaser was included a special edition of The Living Daylights, plus two bonus mini-games; maybe they will work: https://spectrumcomputing.co.uk/index.p ... 6&id=11292

These games were designed for the Spanish Gun Stick, you might try them as well: https://spectrumcomputing.co.uk/index.p ... up_id=1006
retro_collector
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Re: Light Guns and Speccy

Post by retro_collector »

Gratzie Alessandro!

I will try those.

Nowe I just need a Spectrum that works with the light gun and my CRT :)
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Joefish
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Re: Light Guns and Speccy

Post by Joefish »

Didn't those early light-guns with interfaces just detect one moving bright spot on a dark background, like the old 70s TV game units, rather than try and measure the exact raster position like a lightpen?
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1024MAK
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Re: Light Guns and Speccy

Post by 1024MAK »

Because the hardware does not support light guns/light pens, it’s not very practical to get an exact raster position... :-(

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Re: Light Guns and Speccy

Post by Guesser »

1024MAK wrote: Mon Sep 16, 2019 9:52 am +2A, +2B, +3: Only RGB (TTL level) is available from the RGB/video/monitor socket. Composite video is not available. It can be added, but requires extra circuitry.
You mean analogue surely.
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1024MAK
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Re: Light Guns and Speccy

Post by 1024MAK »

Guesser wrote: Mon Sep 16, 2019 9:42 pm
1024MAK wrote: Mon Sep 16, 2019 9:52 am +2A, +2B, +3: Only RGB (TTL level) is available from the RGB/video/monitor socket. Composite video is not available. It can be added, but requires extra circuitry.
You mean analogue surely.
Well, it’s not any known standard... It’s not normal analogue video level signals. And it’s not simple true TTL either...

Mark
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Joefish
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Re: Light Guns and Speccy

Post by Joefish »

Joefish wrote: Mon Sep 16, 2019 6:55 pm Didn't those early light-guns with interfaces just detect one moving bright spot on a dark background, like the old 70s TV game units, rather than try and measure the exact raster position like a lightpen?
What I mean is, something like that could still work with an LCD TV.
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Re: Light Guns and Speccy

Post by Guesser »

I think Amstrad just weren't very good at Ohm's law ;)
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Re: Light Guns and Speccy

Post by Guesser »

Joefish wrote: Tue Sep 17, 2019 8:37 am What I mean is, something like that could still work with an LCD TV.
Does an LCD produce bright enough light at a wavelength the gun is sensitive to though. I suspect not.
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Re: Light Guns and Speccy

Post by zxbruno »

There was a topic about this on WOS years ago. We were told we'd need something similar to wired motion sensors, like the ones used on the Nintendo Wii and Xbox, to get light guns to work on modern TVs and monitors. We'd probably have to develop new light guns as well.

But for those who still have older CRTs, you can play the old light gun games or do crazy stuff like this:

https://www.youtube.com/watch?v=NsRhU-54Ues

I would've used monochrome graphics instead, but it was an interesting proof of concept.
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Re: Light Guns and Speccy

Post by AndyC »

Guesser wrote: Tue Sep 17, 2019 10:38 am
Joefish wrote: Tue Sep 17, 2019 8:37 am What I mean is, something like that could still work with an LCD TV.
Does an LCD produce bright enough light at a wavelength the gun is sensitive to though. I suspect not.
Another problem is the enormous lag on LCD displays, the chances of knowing which frame is being displayed when you actually detect a white spot is fairly slim.
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Joefish
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Re: Light Guns and Speccy

Post by Joefish »

AndyC wrote: Tue Sep 17, 2019 3:03 pmAnother problem is the enormous lag on LCD displays, the chances of knowing which frame is being displayed when you actually detect a white spot is fairly slim.
I really wasn't expecting even that level of sophistication! My Grandstand TV game was literally just a white square dot, bouncing around like the ball in Pong, on a plain green screen background. Nothing else - not even the score digits were visible (until the end of a round) so as not to confuse the gun. You simply had to set the TV contrast and brightness so it could tell white from green. It wasn't even about the colour wavelength as the green background would trigger a 'hit' every time if the screen was too bright.

NES Duck Hunt worked by flushing the normal graphics screen to black with a white patch for the target for one frame. It wasn't trying to count raster lines, just a hit yes or no during that frame. For multiple targets it would flash them up white one by one on a black background, taking a bit longer.

The Speccy equivalent to the Grandstand would be a single bright yellow duck sprite on a black background. Either the gun is pointing at the bright object or it isn't. There wouldn't need to be any frame-flashing for a single target, so raster or frame timing wouldn't come into it. I actually did it years ago by drawing a graphic target sprite on the Speccy screen, and having the Grandstand switched on next to it, and the console would beep if you shot the target on the Speccy's display with the lightgun plugged into the Grandstand.

Although you could probably calibrate whole-frame timing with the gun beforehand, to then handle two or three flashable targets like Duck Hunt. It should at least be consistent for one mode of the TV. You might have to use two frames of blackout to get round any frame-to-frame smearing, although modern LCD TVs shouldn't have too much of that (particularly now they all use LED backlighting). The timing you'd need to calibrate for is the throughput lag of the analogue-to-digital image processing, which may be two or three frames behind the feed.
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Re: Light Guns and Speccy

Post by ZXDunny »

The lightguns of the day for the Speccy worked by watching the raster beam. They didn't see a "picture" at all, just a moving dot of light as the picture was built up.
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Re: Light Guns and Speccy

Post by 1024MAK »

Light guns / light pen just see light. ANY suitable light. Most have circuitry to ignore ambient light levels and only to respond to rapid changes in light level. So a flashing LED torch may activate them...

All the clever stuff is done in hardware and software. If there is hardware support in the video circuitry (so not applicable to ZX Spectrums) this can provide the position of the raster at the time of triggering by way of storing the relevant video system counter values in special readable registers.

If there is no hardware support, all the processing must be done by the game software. If the software can track the appropriate position of the raster, then it can compare when the trigger was activated with the appropriate position of the raster. Hence determining if the target was ‘hit’.

Both the above need a 15625Hz horizontal frequency, 50Hz vertical CRT display.

Otherwise the software can only use a much cruder technique of flashing a bright target on screen and seeing if the trigger was pressed during the time the target was displayed. And ignoring the trigger at any other time.

Mark
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“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
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