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 Post subject: Re: Zapper test ROMs
PostPosted: Thu Jun 23, 2016 11:14 am 
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Joined: Sun Sep 19, 2004 11:12 pm
Posts: 20794
Location: NE Indiana, USA (NTSC)
Would it work to modify the TV's LED backlight to flicker at 15.7 kHz?


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 Post subject: Re: Zapper test ROMs
PostPosted: Thu Jun 23, 2016 11:34 am 
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Joined: Sun Apr 13, 2008 11:12 am
Posts: 7730
Location: Seattle
As long as the backlight is flickering at all, and it blocks a higher enough proportion of light where it's "black" instead of bright, I think it should work. I got adequate pickup with my zapper with light frequencies of both 4kHz and 64kHz.

EDIT: I just tried hooking up my zapper to my desktop's soundcard; the trigger works fine but the photodiode sensor can't see the CCFL in my monitors.


Last edited by lidnariq on Thu Jun 23, 2016 12:57 pm, edited 1 time in total.

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 Post subject: Re: Zapper test ROMs
PostPosted: Thu Jun 23, 2016 12:45 pm 
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Joined: Sun Jan 22, 2012 12:03 pm
Posts: 6963
Location: Canada
It seems a lot less practical to mod a TV than a zapper, though, whatever floats your boat, I guess?

In either case, you'd need new software too. There's just no easy way to make Duck Hunt great again. :(


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 Post subject: Re: Zapper test ROMs
PostPosted: Thu Jun 23, 2016 2:33 pm 
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Joined: Tue Nov 23, 2004 9:35 pm
Posts: 707
This might be a dumb question, but what would happen if you modified the zapper to look for a 60Hz signal instead of a 15KHz signal? The CRT draws roughly 15,750 scanlines each second or 262.5 scanlines every frame. The LCD draws the screen instantaneously 60 times per second. Zapper gun games look for black in the first frame followed by bright white in the second frame. Theoretically, it should work. Practically, I would suspect that the 60Hz transition time is too slow for the gun to give an accurate dark/light response.

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 Post subject: Re: Zapper test ROMs
PostPosted: Thu Jun 23, 2016 2:40 pm 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
The demodulator can't be tuned that slow.


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 Post subject: Re: Zapper test ROMs
PostPosted: Thu Jun 23, 2016 3:58 pm 
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Joined: Mon Jul 02, 2012 7:46 am
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Think about it, at 15kHz, you get 15 cycles per ms. You need those cycles to establish a reliable signal that can be distinguished from noise. 15 cycles at 60Hz would take 250ms. And that's just for a single bit. Granted, you could probably use fewer cycles, but essentially, you are talking about a fundamentally different detection and communication protocol. There just isn't any simple way to "just do the same thing at a different clock speed" unless you can live with the 250x slowdown.


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 Post subject: Re: Zapper test ROMs
PostPosted: Sun Sep 16, 2018 1:20 am 
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Joined: Mon Apr 24, 2017 10:23 pm
Posts: 5
I'm testing a hack that implements adjustable delay for light signal detection. So now it works quite fine, especially on HidefNES and RetroUSB AVS (HDMI signal has shorter delay compare to Composite video on LCD). I hope the author will release his hack soon.


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