Nintendo NES Zapper

As I just received my FC-Mobile II Portable NES emulation system, I started wondering how the gun, aka the Zapper, was working. Indeed this little piece of plastic has been instrumental in many games such as the amazing “Duck hunt”.

So to keep things short here’s the idea : when you pull the trigger, screen goes blank and then with draw just blank squares at the target position. In the Zapper you have a diode detecting light and a lens focusing the beam.
The computer knows that if the diode detects light as it is drawing a square (or after the screen refreshes) then, that is the target at which the gun is pointed. Essentially, the diode tells the computer whether or not you hit something, and for n objects, the sequence of the drawing of the targets tell the computer which target you hit after 1 + ceil(log2(n)) refreshes (one refresh to determine if any target at all was hit and ceil(log2(n)) to do a binary search for the object that was hit).
And most important, it *can* still work on a HDTV as shown in the following video !