MadSci Network: Engineering

Re: How does the Nintendo Zapper gun work?

Date: Fri Jul 23 21:15:37 1999
Posted By: Abtin Spantman, , Electrical Engineering, L. S. Research, Inc.
Area of science: Engineering
ID: 932342468.Eg

I bet you can't use the Nintendo Zapper Gun on a "Lap-Top" computer.
Back in the olden days, when there were real TVs (no not the program), they 
had electron guns and Cathode-Ray-Tubes.  And this is what was inside the 
TV, shooting stuff back at you, and you didn't know it.  
1) Here is how it works: In the older TVs (Non-LCD screens) there is an 
"Electron Gun" that looks like a big light bulb.  The function of this 
electron gun is to use electricity and heat up an element, and boil off 
electrons.  A set of electro-magnetic coils then repel and direct the flow 
of these loose electrons at a very high speed towards the inside of the TV 
screen. This is all happening behind the TV tube glass.  These electrons 
are being generated in the back of the TV tube, and are shot directly out 
towards you.  What stops most of these loose and high speed electrons is 
the front of the tube which is made up of very tiny capsules of phosphorous 
material that momentarily give off light as they are hit by these loose 
high speed electrons.  You can actually see the tiny capsules that look to 
be red, yellow, and blue.  Your monitor is rated at xx dots per inch, which 
means that there are xx of these clusters of red, yellow, and blue capsules 
(called pixels - short for picture elements) in each linear inch of the 
front of your computer monitor. If you look close enough, you can actually 
see these pixels.  
Well, as you guessed it, some of those nasty loose high speed electrons 
make it past the phosphor screen and come straight at you. And you didn't 
believe your mother when she said sit back from the TV screen or you will  
  Inside the Nintendo Zapper Gun or any such device (like a "light pen") is 
a "detector".  That's right.  The Nintendo Zapper Gun does not actually 
shoot anything out, but it actually gets hit by the TV's  bullets that are 
the loose high speed electrons which are generated in the back of the TV 
where it gets really warm. 
2) How does the Zapper Gun know where you aimed?  The electrons are boiled 
off. The magnetic field on the back repels and accelerates the electrons 
towards the front. And  then, there are guide electromagnets on the side 
and the top/bottom of the tube.  With precise timing and monitoring, these 
guide electro-magnets can direct a very fine beam of loose electrons to 
each of the red, yellow, and blue pixels.  The back electro-magnet 
determines how much energy that electron has when it hits the particular 
pixel.  By controlling and mixing the amount of high speed electrons going 
into each of the primary color pixels, different colors can be made.
This beam is controlled to sweep from left to right horizontally, then go 
down one row, then start the horizontal sweep from the left to the right 
again, and so on.  The exact location of the beam at any given time is 
known by the TV circuitry.  When you pull the trigger on the Zapper Gun, 
the Nintendo system, then reads this information from the TV circuitry, and 
checks to see if the gun has been hit by an electron beam or bullet.  If 
the Zapper gun has been hit by the electron beam, that means you were 
aiming at the right spot when the sweep was going through, and you have a 
direct hit.  If the zapper gun is not hit by the electron beam, that means 
that you must be aiming elsewhere on the screen, and it is considered a 
3) The reason it will not work with LCDs: Liquid Crystal Displays, such as 
those used on Lap-Top computers use a different technique to get light out 
of pixels.  They do not shoot high-speed electrons into your face, which is 
what the Zapper Gun needs to function - and so the Nintendo Zapper Gun 
probably will not work on your Lap-Top.

Yes I still sit too close to the TV screen.

Let me know if any questions arise,
Abtin Spantman

Ollie Strickland adds:
Mr. Spantman,  I was cruising through the mad scientist web page, and
saw your response to the kids question regarding how the Nintendo zapper
gun works.  I believe your answer is partially incorrect.  The
explanation of how the CRT works, fine... but then you went on to say
that the NES reads the TV circuitry to get beam information, then checks
a sensor in the zapper for a "bullet" or electron beam.  Well, 1st of
all, the communication between the NES and the TV set is unidirectional,
not bidirectional.  It can only output data to the tv, not "go in" and
get any from any circuitry.  Secondly... there is no correlation between
the gun being pointed at the correct target on the screen (a hit) and an
electron beam being sensed by the zapper.  
So... how does it work???  When the trigger is pulled on the zapper, the
NES tells the tv to momentarily not draw the numerous targets on the
screen, but instead an object of a specific size and color, maybe even
blink at a specific rate.  This all happens very fast, but if you look
in the popular game Duck Hunt, you will see that right when the trigger
is pulled the ducks disappear and white rectangles appear.  This is what
the sensor recognizes. The sensor sends data about what was in it's
field of vision, and the NES looks for that special target data
(flashing box, whatever).  This solves the unidirectional problem
between the TV and NES.

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