Cecil has explained how the old lightguns work but how do the lastest lightguns work? I find it hard to believe that the arcade guns and the ‘pixel perfect’ targeting of the playstation guns are using the same method.
Welcome to the SDMB, and thank you for posting your comment.
Please include a link to Cecil’s column if it’s on the straight dope web site. To include a link, it can be as simple as including the web page location in your post (make sure there is a space before and after the text of the URL).
Cecil’s column can be found on-line at this link:
In Nintendo’s “Duck Hunt,” how does the TV know when you’ve hit a duck? (11-May-2001)
moderator, «Comments on Cecil’s Columns»
I know that the Super Scope 6 for the Super Nintendo uses an infrared receiver to work. The receiver plugs into the system and is placed on top of the TV. The only downside to this setup was that you had to calibrate the gun with the receiver before you play the game and you have stay in the same place in the room for accruate shots. If you move around, you had to calibrate the gun and receiver again. Also it was in a shape of a bazooka and you had to hold it on your shoulder, which made for very bad cramps for your shoulder and arm.
Cecil goofed this one. The device is known as a “Light Pen” and is familiar to computer hardware hackers from the '60s and '70s. I built one myself from $2 of parts and the barrel of an empty magic marker. The gun is just like a light pen except that you don’t touch the screen with it (actually, you could use the gun as a pen, it would work fine if you held the tip of the gun right against the screen). The photocel in the light pen/gun barrel just senses when the raster passes underneath it, there are a variety of ways to use techniques like this to sense the point where the pen/gun is pointed.
The only reason Nintendo (or whoever) has a patent on this device is because of the unique application of the sensor in a gun body, for games. Nothing unique about it really except the form factor.
While a light pen works the way you describe, I find it difficult to believe that a light gun made for a home videogame could work in the same way – not to mention that in the game described, the screen does visibly blink to provide a targetting image. To use a conventional light-pen system as a game gun would require, in effect, autofocusing telescope optics.
No john, the light pen approach would merely need a narrower field of view for the sensor. Like deep in the end of the barrel of the toy gun, instead of at the tip of a pen. The gun isn’t really that accurate, it can only sense large areas on the screen, maybe detect 1/8ths or 1/16ths of the screen, not pixel by pixel like a light pen in close contact with the screen.
The early light pen programs DID work by flashing the screen, there were a variety of approaches to sensing the position and that was the simplest. I know because I wrote a similar routine in BASIC on an 8080A microcomputer in about 1976. The processors in a nintendo aren’t very powerful and would have required the simplest algorithms.
As a side note, my brother, being both an electronics and gun enthusiast, thought it would be neat if the Nintendo gun was full auto. He took it apart, rewired it, and voila! A remorseless killing machine.
Louie, I always thought the calibration on the Super Scope was due to it being infrared. But I also own Lethal Enforcers for the SNES which uses a corded light gun, and it requires me to calibrate before starting and again if I change position. Like Cecil’s second description of how a light gun may function, the game computes where I shoot on the screen (not just I’ve hit a target) and displays a bullethole (well, it Nintendo’s more censored days, a green mark) at the location. Is it this function that requires it to be calibrated, not the cordless feature?
Hail Ants, doesn’t Duck Hunt only afford you 3 bullets – wouldn’t your brother’s auto light gun still require pretty amazing accuracy? 
“Early”, forsooth? The IBM 3277 alphameric terminal had light pens in 1971, the 2250 graphic workstaton in 1965, and others were available years before that.