The NEW Build Your Own Arcade Controls

Main => Lightguns => Topic started by: vetteguy112233 on June 23, 2008, 10:18:03 am

Title: Is it true I can't use a lightgun since my monitor doesn't have V and H sync?
Post by: vetteguy112233 on June 23, 2008, 10:18:03 am

I had to twist the cables together for my V and H sync and thought I read somewhere that a lightgun, like ACT-LABS will not work without individual wires for the V and H sync.

Title: Re: Is it true I can't use a lightgun since my monitor doesn't have V and H sync?
Post by: northerngames on June 23, 2008, 06:46:27 pm

the new usb is supposedly able too but not the older versions "ray gun style"

the lcd topgun will also work.

Title: Re: Is it true I can't use a lightgun since my monitor doesn't have V and H sync?
Post by: vetteguy112233 on June 26, 2008, 11:10:17 pm

I finally received an email from ACT-LABS, here is what they said:

The PC USB light guns require the H and V sync signals from the VGA connection.  This is how the light gun tracks where it is pointing with the use of these signals.
If the light gun can intercept these two separate signals then it will work, if it doesn't receive these signals then it will not work for you application.

So apparently if you don't have both wires, then you cannot use the guns from ACT-LABS.

Title: Re: Is it true I can't use a lightgun since my monitor doesn't have V and H sync
Post by: MonMotha on June 27, 2008, 12:37:39 am

This whole "twist the wires" together thing is somewhat bogus to begin with.  It only works due to an academic curisity (N-channels tend to be stronger than P-channels on the same process, that or some sync outputs are open-drain to being with) anyway.  The proper way to make composite sync is to XOR the two sync signals together, minding polarity.  If you take active low ("negative") horizontal sync and XOR it with active high ("positive") vertical sync, you get negative composite sync.  Hooking two CMOS outputs together is actually a kinda bad thing to do and tends to eventually result in dead output drivers (though in practice that seems to take a rather long time).

Why did I bring all that up?  Well, if you do it "the right way" using a 7486 (or similar: 74LS86, 74HCT86, 74F86, 74S86), you'll have both composite sync (at the output) and separate sync (at the inputs) available.  This way, you can feed your monitor and light gun what they want.