Lazer Tag Equipment Modifications

From spcecdt Thu Aug 15 19:14:54 1991
From: (John DuBois)
To: ******
Subject: Re: lasertag, again
Date: Thu, 15 Aug 91 19:14:54 PDT

     I added a "fast-fire" circuit to get around the annoying delay
that prevents you from firing again immediately.  It used the target
LED contact on the trigger switch to reset the pulse generator.  That
way, normally when you fire the sound goes on for its normal duration
(we banned any mod that would turn off the sound or always shorten it).
But, if you immediately pull the trigger again, when the LED contact is
made a pulse is sent to reset the firing pulse generator.  By the time
the secondary (firing) contact is made, the pulse generator has been 
reset and can fire again.
     I upped the power by replacing the entire LED driver circuit with
a bipolar transistor driving the gate of VMOS transistor, and replaced
the output IRED with with one that could handle the higher power (from
Mouser).  The total output power roughly doubled.
     I added a fast-fire circuit to the pistol of anyone who wanted me
to, along with a cheaper & simpler power mod (reducing the current 
limiting resistor to increase power by 50%; about as far as it could
go and still have any kind of regulation).
     We also banned wide-angle mods and autofire pistol mods, since they
seemed to eliminate the need for any sort of skill; the mods we accepted
were intended to reduce the merely annoying characteristics of Lazer Tag.
     For a while we about 50 Lazer Tag players here, of whom about 30
would typically show up at games (usually held once a week).  It was very
intense.  Now we have games a few time a year at which a dozen or two show...

From spcecdt Tue Sep 15 20:14:29 1992
From: (John DuBois)
To: ******
Subject: Re: lasertag
Date: Tue, 15 Sep 92 20:14:29 PDT

     Gee, that was a long time ago.  Let's see.  The modifications I made

     Mod #1: Power increase.
     I reduced the value of the resistor in the emitter driver.  I put a
resitor in parallel with it to reduce the resistance by about 2/3.  That
increased power somewhat, but not enough for me, so I ended up adding
another stage to the emitter driver.  The extra stage used an IRF511 to
drive the emitter.  I fried the emitter while experimenting (it's possible
that that much current would have fried it anyway) so I replaced it with a
high-power emitter I got from Mouser.  It had an integral lens (round
front, like most LEDs) so I had to cut off the front and polish it up
again.  The integral lens magnified the source size and so had the effect
of increasing the projected spot size.  The increased spot size had a
"shotgun" effect, giving an unfair advantage and reduced skill level at
close range and being ineffective at long range.

     Mod #2: Fast-fire.
     This is what I reverse-engineered the gun to work out.  It was easy to
make the gun fire as fast as the the trigger was pulled, but the simple
reset circuit caused the sound to be cut off as soon as the trigger was
released.  I didn't think this was fair, so I designed a circuit that
would reset the gun only when the trigger was pulled again.  This makes
the sound continue until the trigger is pulled again, and then start over.
     I found that the fire circuit needed a brief period of time to reset.
If it was reset at the same time as it was retriggered, it would not fire.
So, I connected my reset circuit to the gunsight contact instead of the
fire contact.  The gunsight contact (which turns on the LED in the
gunsight) is made slightly before the fire contact is made, so that the
fire circuit has reset by the time it's triggered.  I found that if the
trigger was *really* slam down, it would still fail because it does take a
small fraction of a second to reset.  It takes a little discipline to
avoid slamming the trigger down in the heat of combat :-)  But, you don't
have to pull so slowly as to actually make a difference in effectiveness.
     The reset circuit fits on a tiny piece of perfboard and can easily fit
into the empty space next to the power supply bypass capacitor in the
                         ,--+---/\/\/-----O +V
                        /   |                break trace---v    C9
           100K      |/     `------|(-----------------,----X----|(-------
LED  <----/\/\/------|2N2222      0.1uF            ___|___
ILLUM   |            |\                           |  13   |
        |              _\|                        |       |
        |    10K          \                       |  U3   |
        `---/\/\/----------|                      |_______|

The trigger switch and power supply bypass capacitor are arranged like this:

_| ,-> | |
 | |   | |
   |   | |
   |   | |
   O   O O-- Fire
 LED   |
ILLUM  |     +
       |            _|_
       O+V          ///

To install the circuit, connect it to +V, gnd, and LED ILLUM (on the
trigger switch), cut the trace on the PC board that connects U3 pin 13 to
C9, and connect the reset circuit to U3 pin 13.  Note that +V and gnd are
available in the handle (at the leads of the power supply bypass
capacitor), along with LED ILLUM which is right on the trigger switch (the
contact that is actually pressed by the trigger), so if you place the
circuit in the handle the only extra lead that has to run up to the main
circuit board is the one to connect to U3 pin 13.

     Mod #3: "Predator" LED Illuminator.
     Since the emitter is in a plastic block carefully placed at the focal
point of a lens, I thought I'd try making the pistol emit a "targetting
beam" by placing a visible LED next to it.  For symmetry, I ended up
placing three tiny (1/16") LEDs into holes drilled into the emitter
mounting block around the emitter.  I connected them to the LED ILLUM line
along with the gunsight LED.  They can be connected in series to save
power.  They ended up being useless for targetting since they are only
visible in darkness on light surfaces at relatively close range, but the
pattern they make is somewhat striking since it's the same triangle
pattern produced by the alien's weapon in Predator :-)  Of course, the
LEDs are easily easily seen even at long range when looking down the
barrel, which is something of a giveaway but also an effective fear inducer.

    Mod #4: NiCd cells.
    I found that the gun would not work with NiCd cells because of their
lower voltage.  I couldn't find any NiCd cells with the appropriate form
factor to fit the right number into the battery case, so I made the
battery compartment larger.  I removed the incandescent lamp that flashes
when the gun is fired, and extended the battery compartment into the part
of the gun it occupied.  This let me fit eight standard AA cells in, just
barely.  Eight NiCd cells produce 9.6V, which powers the pistol quite well.

     Hope you find this useful.

From spcecdt Wed Sep 16 20:15:42 1992
From: (John DuBois)
To: ******
Subject: Re: lasertag
Date: Wed, 16 Sep 92 20:15:42 PDT

     My NiCds were not new ones, so they were probably about 7.2V when I
put 6 in.  I wasn't worried about the reduced range; the pistol just wouldn't
work with them.  I guess its threshold is somewhere between 7.2V and 7.5V.
Although NiCds have a pretty flat discharge curve, that's a pretty narrow
margin so I wouldn't think even new ones would be useful for a full
     I'm not a hard-core optics type, but I'm amazed that anyone told you
a doubling of range would need a 10-fold increase in power.  Perhaps to get
through mist or something, but under normal atmospheric conditions a
doubling of range requires exactly 4x as much power (due to the inverse
square law) when the image size is much larger than the source size, as it
is with the Starlyte.  I doubled the power of my emitter and got about the
expected 40% increase in range.  I had to replace the driver circuit to get
that; just reducing the current limiting resistor in the stock driver I
was only able to get 1.5x power.
     My estimate of the power output of the stock pistol is 75mW peak,
15mW average (since it has a 20% duty cycle).  I based this on measurement
of the current with my 'scope and typical IR emitter efficiency.
     We banned autofire mods, among other reasons because some people were
playing with unmodified guns (though I modified the guns of anyone who
asked) and autofire was a bit too much for them to go against.

From spcecdt Thu Sep 17 19:43:38 1992
From: (John DuBois)
To: ******
Subject: Re: lasertag
Date: Thu, 17 Sep 92 19:43:38 PDT

     You can still buy old 6032 IR imaging tubes for $30 or so.  They're
kind of a pain because they need a focusing supply in addition to a cathode
supply.  In fact, I have one that I bought ca. 10 years ago that I've never
done anything with because it would be a pain to make a small, efficient
power supply for it.  But it can be done.
     As I recall, the Starlyte puts out a fairly complex waveform.  The
ones I looked were 55KHz, 20% duty cycle, but with that then pulsed at some
other rate.
     A larger diameter lens allows you to produce a narrower, more intense
beam.  The reason is that to produce a more collimated beam you have to
use a longer focal length lens.  But, a longer focal length lens has to be
placed further from the source.  To capture the same amount of the
emitter's light cone, a lens that is further from it must have a larger
     I haven't done much with LazerTag equipment lately.  The people
around here seem to have completely burned out on it; we haven't played a
game for a year or two.  I think that to get them interested again would
take a substantially different game.  I find the most annoying thing about
LazerTag the relative ineffectiveness of the sensors.  They're somewhat
directional, and all someone has to do to protect himself is turn around
and run away.  The head-mounted sensors were not that great either.  The
ideal would be something like the Army MILES gear, which includes a harness
with sensors all over it.  I tried it once and it was quite effective.
Unfortunately, a harness like that is much more complex and expensive.

How to add a fast-fire module to a Lazer Tag pistol
Back to my experience with Lazer Tag
This web page maintained by John DuBois