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HTG Explains: How the Nintendo NES Zapper Worked and Why It Doesn’t Work On New TVs

Just because your old Nintendo Entertainment System is alive and well doesn’t mean it can play nice with modern technology. Today we explore why the classic light gun accessory for the NES didn’t make the jump to the 21st century.

Dear How-To Geek,

This probably isn’t going to be the most serious question you get today, but I am looking for a serious geeky answer: why the heck won’t my Nintendo zapper work on my HDTV? I pulled my old NES out of storage to play some classics and decided to start with the very first cartridge, the combo Super Mario Bros./Duck Hunt one. Super Mario Bros. works fine (although man do the graphics look blocky and strange on a big HDTV) but Duck Hunt doesn’t work at all. The game loads, you can start it, but you can’t shoot any ducks. Not a single one.

I was convinced the zapper was broken but then I plugged the NES and zapper into an old 1990s-era tube television out in my garage and, behold, the zapper works! From my little test I know enough to say that the issue seems to be a CRT vs. HDTV issue, but I have no idea why. What’s the story? Why won’t the zapper work on newer TVs?

Sincerely,

Retro Gaming

While we have fun answering just about every question that comes across our desk (you don’t end up at How-To Geek if you don’t love how stuff works, after all), we really love questions like this: geeky inquiry for the sake of geeky inquiry.

First, let’s reframe the question slightly so we’re using more precise terms. The issue you’ve uncovered isn’t about the difference between CRT and HDTVs (because there were, in the early days, consumer HDTVs built around CRT technology). It isn’t about resolution, it’s about how the display is rendered. To frame it more accurately would be to say that it’s about the difference between CRT/analog video and LCD/digital video.

Before we look at the core of the issue, however, let’s look at how the Zapper functions and interacts with the NES and television. A lot of people, and certainly most of the kids that played the NES back in the day, were under the impression that the Zapper actually shot something towards the television, much like a TV remote sending a signal to a television set. The Zapper does nothing of the sort (and what, exactly, on the television would be able to receive the signal and send it to the NES?). The only connection between the Zapper and the NES is the cord, and for good reason. The Zapper isn’t as much a gun as it is a sensor, a very simple light sensor. The Zapper doesn’t shoot anything, it detects patterns of light on the screen in front of it. This was true of all light-gun accessories for all video game systems of the era (and preceding it). They were all just simple light sensors housed in deceptively gun-like cases.

Does that mean the Zapper was actively tracking all those ducks on the screen with surgical precision? Hardly. Nintendo designers came up with a very clever way to ensure the simple sensor in the Zapper could keep up. Every time a player pulled the trigger on the Zapper, the screen would (for just a fraction of a second) blink black with a large white targeting box drawn over everything on the screen that was a valid target (such as the ducks). It repeated the process, all within that fraction of a second, for every available target on the screen.

While the player saw a screen like this the whole time:

The zapper, during each trigger press, saw something like this:

In that brief flash, which was invisible the user, the gun would determine if one or more of the targets was centered in the Zapper’s hit zone. If the box was centered enough, it counted as a hit. If the target box was outside of the center zone, it was a miss. It was a very clever way to deal with the limitations of the hardware and provide a fluid user experience.

Unfortunately, despite being clever, it was very hardware dependent. Much like early PC video game designers used hardware quirks to help build their games (like knowing the clock speed of the platform they were working on was fixed and could be used to time in-game events), Nintendo and other early game companies relied heavily on the quirks of CRT displays and their respective display standards. Specifically, in the case of the Zapper, the mechanism is completely dependent on the characteristics of CRT display.

First, it requires extremely precise timing between the trigger pull on the Zapper and the response on the screen. Even the slightest difference (and we’re talking milliseconds here) between the signal sent to the NES and the signal displayed on the screen can throw it off. The original timing sequence was based on the very dependable response time of a CRT hooked up to the analog NES signal. Whether the old tube TV was big, small, cutting edge or 10 years old, the speed of the signal via the CRT display standard was reliable. By contrast, the latency in modern digital sets is not reliable and is not the same as the old consistent delay in the CRT system. Now, this doesn’t matter in most situations. If you have your old VCR hooked up to the coax jack on your new LCD display, it doesn’t matter one bit if the audio and video are delayed by 800 milliseconds because you’d never know (the audio and video would play in sync and you’d have absolutely no way of knowing that the entire process was lagging by a fraction of a second). However, this latency completely destroys communication between the Zapper, the NES, and the events on the screen.

This extremely precise timing was possible (and consistent) because Nintendo designers could count on the refresh rate of the CRT being consistent. CRT displays use an electron gun to activate phosphors in screen hidden behind the display glass. This gun sweeps across the screen from the top to the bottom at a very dependable frequency. Even though it happens faster than the human eye can detect, every single frame of every single video game or television broadcast is displayed as if some hyperactive robot is drawing it line by line from the top to the bottom.

By contrast, modern digital displays make all the changes simultaneously. This isn’t to say that modern televisions don’t have progressive and interlaced video (because they most certainly do), but the lines aren’t rendered one at a time (however quickly). They are displayed all at once in their respective standards. As for why this matters to the Zapper, the software driving the Zapper’s detection algorithm¬†needs that line-by-line refresh to pull off the timing tricks which make it possible to have 5 ducks on the screen and successful hit detection all within 500 milliseconds or so.

Without the very specific and hard-coded timing provided by the CRT display, Duck Hunt (or any other Zapper-based game of the era) simply won’t work.

While that’s disappointing, we know, there is an upside. The premium tube sets of yesteryear, those high-end Sony sets for example, that cost $$$$ can now be found sitting on curbs during electronic recycling days and gathering dust at the back of second hand shops. If you’re serious about retro gaming, you can pick up a premium standard definition CRT for pennies on the dollar.


Have a pressing tech question, big or small? Shoot us an email at ask@howtogeek.com and we’ll do our best to answer it.

Jason Fitzpatrick is warranty-voiding DIYer and all around geek. When he's not documenting mods and hacks he's doing his best to make sure a generation of college students graduate knowing they should put their pants on one leg at a time and go on to greatness, just like Bruce Dickinson. You can follow him on if you'd like.

  • Published 02/3/14

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