Nintendo Entertainment System / Duck Hunt

Today is the 25th birthday of the NES, the Nintendo Entertainment System. That's 25 years of gaming-at-home Nintendo fun (as long as you don't count its sister model, the Family Computer, which was the Japanese version of the NES that debuted two years before its American counterpart.) In honor of the venerable NES, today I'll be discussing one of its most iconic games and how it worked.

Duck Hunt, a game instantly recognizable by gamers and non-gamers alike for its light-sensitive gun, was one of the original NES games. It came pre-packaged with the system and after a few years was even included on the same cartridge as Super Mario Bros. for the now-famous Super Mario Bros./Duck Hunt combo cartridge. What made the game so special was its innovative Zapper gun. The Zapper was a hand-held "gun" that plugged into the TV and worked just like the real thing. Point it at a duck on the screen, pull the trigger and poof! Dead duck. While current socio-political sensitivities might suggest that a hunting game complete with a model gun is a poor choice of game to pre-package with something ultimately aimed at children, there's no denying that the game itself was fun and different.

The Zapper gun and all of its incarnations were the only reason Duck Hunt hit it big. The game itself got mixed reviews, but most agreed that it was rather repetitive and only enjoyable for short amounts of time. So, how did this Zapper gun work and what made it so iconic?

The first thing you need to know is that the Zapper gun is a passive device. That means that it emits nothing (no light, no radar, or anything else) to do its job. Instead, it passively gathers information (in the form of light) through a lens in the barrel of the gun. A light sensor inside the hilt of the Zapper reads the light coming in from the barrel and sends it to the NES to make sense of it. If the Zapper gun were an active device, it would constantly be shooting the television (or whatever else you aim it at) with some sort of beam. Because this isn't the case, though, the TV is actually shooting at the Zapper.

As the NES processes the game, it sends a video signal of its output to the television. The output it sends consists of an exact amount of on-screen pixels and a finite number of colors. Intuition might tell a person that plays the game that the gun is simply reading the colors off of the screen and making sense of where it's pointing, but the truth is actually much simpler (and much more sneaky) than that.

What happens as a gamer points the Zapper at the screen is absolutely nothing. the NES is just chugging along sending out its video signal, and the gun isn't interacting with the NES at all. That is, it doesn't interact until the player pulls the trigger on the Zapper to shoot a duck.

What happens then is both interesting and limiting for the game. As the player pulls the trigger, it activates the sensor and sends a signal to the NES at the same time. As the NES receives this signal it changes the display on the television for a split-second to almost total blackness before reverting instantly to the correct colors. What it does in that short time is cue the Zapper gun in on the exact location of the duck by showing a small white box on the screen amidst the blackness. If the gun detects the proper amount of white light hitting the sensor at the moment the trigger is pulled, it sends the NES another signal telling it that the player hit the target. If not, then it sends back a negative.

This method of target-detection lead many players to completely bypass the game's mechanics by simply pointing their gun at a white computer screen or a light bulb and pulling the trigger over and over again, each time getting points as the Zapper gun thought it was pointed at the small white box on the TV.

Another issue was that the lenses in the guns could get bumped out of place and forever after doom the gun to shoot sideways and be impossible to use without cheating.

By comparison, today's Wii remotes are far more accurate and advanced. For on-screen cursors and selections, they actively fire two infrared beams in the general direction of the TV. A sensor above or below the TV catches the beams with two "eyes" and uses that information to figure out exactly where the remote is pointing, similar to how the human eyes work together to perceive depth. This is not only more accurate and adaptable, but it happens in real time and allows a cursor (or cross-hairs in the case of the new Duck Hunt) to always be visible on-screen. No more broken lenses, no more cheating. and much less guess work.

Duck Hunt as packaged with Super Mario Bros. (1985, repackaged 1988)

A current Duck Hunt analog on the Nintendo Wii (2006)

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Adams, C. (2006). In Nintendo's "Duck Hunt," how does the TV know when you've hit a duck? Retrieved October 18, 2010 from The Straight Dope, TheStraightDope.com: http://www.straightdope.com/​columns/​read/​2304/​in-nintendos-duck-hunt-how-does-the-tv-know-when-youve-hit-a-duck.

How does the light gun for a video game work? (2010). Retrieved October 18, 2010 from How Stuff Works, HowStuffWorks.com: http://how does the light gun for a video game work?.