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Optical Guns question

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mairsil:

--- Quote from: u_rebelscum on August 24, 2004, 02:55:41 am ---Pluses:
tracks real time
riffle or shotgun
HD TV

Minuses:
Xbox, not PC
glowing green

neutrales:
seems to want a screen flash


I wonder how this one (and other xbox guns) works (the timing issues, ect)?

--- End quote ---

I actually have both the MadCatz gun and the Pelican rifle, along with the only two Xbox gun games (House of the Dead 3 & Silent Scope Complete). The MadCatz works just like you would expect a lightgun to work complete with screen flashes to get positioning. It is not bad, but feels a little lagged at times.

The Pelican rifle is by far the better of the two guns. Since it is able to work with HDTV's, it has a much tighter accuracy than the MadCatz gun. The rifle functions differently depending on which game you are playing. In HotD3, the gun uses the standard screen flash. In SSC, it does have realtime tracking, but because of how the game designers implemented it, it requires the TV brightness to be so high that the game gets washed out. Even with the TV and game brightness at max (nearly pure white), the game still cannot track the gun very well. This is the complaint that most people have.


--- Quote ---Does the calibration correct for the photodiode alignment -- depending on the angle it could get pretty far away from the right place.
--- End quote ---

For the Happs guns, I am not sure if the calibration has any correction for a misaligned photodiode. From my experience using pretty beat up guns in the acrades (like Dave & Buster's where they are more likely to replace a game with a new one than fix a broken one), you can get some really off shots. The design of the gun helps to compensate for this some. If you look at the exploded view for the Happs gun, you will see that the photodiode is set back a couple of inches from the end of the barrel (it appears to be roughly above the trigger and I am not going to take one of mine apart to find out). Also, the actual barrel opening is only 5/8" in diameter. This really helps to limit the amount of screen that the gun can see at any one time, but is not absolute if the photodiode is far out of alignment.

u_rebelscum:

--- Quote from: shadowdrak on August 24, 2004, 02:47:06 am ---I don't quite understand why calibration is necessary.  Forgive me if this sounds dumb.

My brain tells me this:

If the control pcb can read the VGA signal it has horizontal and vertical sync, resolution, etc.

So why wouldn't it be enough to know such things. you can count the lines down, by dividing the time by the horizontal retrace interval, correct?
the pixel on that line would be: (time to pulse)mod(retrace interval)*(horizontal resolution)/(retrace  interval)

I guess you could replace the mod part with (time to pulse)-(horizontal lines)*(retrace interval) as it might save time (i dunno really)

as long as you sync the timer to the beginning of the frame, it should have no problem finding the pixel as long as you know the resolution and the proper refresh rates.
--- End quote ---

Your calculation misses some things:

Time to move beam from bottom of sceen to top of screen; this time is usually equivalent to ~30-50 lines.  Also different video cards (and sometimes different video card drivers) set a different number of those "blank lines" at the begining the new screen or at the end of a screen.

Time to move the beam back to the begining of a new line.  This usually is a little less than the time needed to draw the actual visible line, but there is also the time the beam spends "straightening out" before the image starts and after the image ends.

Latency between sensor and chip. Very important, as this can be many lines, but even half a line (call it ~1/100000 of a sec) is bad.


--- Quote ---Act labs doesn't say why you need to calibrate, only that you do.  I also found nothing on google(maybe I am a sucky searcher).
--- End quote ---

To account for any and all of the above variences.  The calibration done in the original arcade games also does this.

Note that the actlab calibration method does not account for bent sensors, letterbox or other black bars, or overscans.  But the original arcade calibration does.  Anyone want to guess? (ask and I'll try to make sense tomorrow, it's past my bedtime)

shadowdrak:
I hadn't considered the vertical retrace.  My brain tells me calibration in this case would have to be hardware driven (other wise it might screw up the timing.  I have no experience with VGA stuff, but might it be possible to "intelligently detect" the amount of blank lines before the frame? The number of blank lines probably changes depending on the refresh rate too I would suppose so an ad-hoc adjustment for your hardware probably wouldn't work.  I guess a simple solution to deal with sensor latency would be to have some sort of tuning device (maybe a pot with some logic associated with it) to adjust the timing offset.  I think the most I will do is probably try to hack the actlabs gun to fit into a guncon style case.  I am having too much trouble tracking down a suitable timer IC(most specs I see are way too slow to be of much use).  I figure for the timer to differentiate between pixels, it would have to operate at the horizontal frequency times the horizontal resolution AT LEAST.  this means I need to count at like 30-60mhz depending on the resolution.  I'll look into it a bit more, but I think I may be out of my league when it comes to the amount of time, effort, and money this will take.

MoonDog:

--- Quote from: shadowdrak on August 23, 2004, 03:43:44 pm ---If I had defined specs, I could probably design a circuit for it, but that seems like it might be impossible unless we could convince someone to "take one for the team" and buy one to analyze it.  That would be a lot to ask of relative strangers.  Any takers though?
--- End quote ---

what about taking a collection?  you might be able to get enough people who are willing to pitch in.

Generic Eric:

--- Quote from: MoonDog on September 12, 2004, 01:12:34 am ---
--- Quote from: shadowdrak on August 23, 2004, 03:43:44 pm ---If I had defined specs, I could probably design a circuit for it, but that seems like it might be impossible unless we could convince someone to "take one for the team" and buy one to analyze it.  That would be a lot to ask of relative strangers.  Any takers though?
--- End quote ---

what about taking a collection?  you might be able to get enough people who are willing to pitch in.

--- End quote ---
.50 to a paypal?  I bet there would be enough intrest within the whole community (make post on mameworld.net and here of course of your intentions.) From that wide range of a community, I bet you could raise enough scratch to raise at least part of the money.

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