LaserTag Technical Overview
by Simon Russell
This information relates only to the
Worlds Of Wonder Laser-Tag system, which is the system that all UK Laser-Tag
clubs use as the general combat system.
The waveforms that make up a W.O.W.
compatible signal are shown below:
The tag waveform is made of two signals,
a 57.6kHz signal:
which is modulated by an
1800Hz signal:
to give the tag signal:
This tag waveform is transmitted for approximately 100ms.
The Gun (Emitter)
There are many ways to produce this
waveform:
The cheapest & most simple is to make
up two oscillators using 555 timer chips, with the output of the chip producing
1800Hz output tied to the reset of the chip producing the 57.6kHz signal.
Connecting a third 555 to the reset of the chip producing the 1800Hz signal can
control shot length & auto-fire capabilities. Connect resulting signal to a
high speed power transistor & an infra-red led, you’ve got a primitive tag
gun! This arrangement does work, but is susceptible to frequency drift over time
& will need to periodically be readjusted.
555 Circuit:
A much better alternative is to make the
circuit crystal based. Using a 1.8432MHz crystal, divided down by a factor of 32
to produce 57.6kHz, then divided by 32 again to produce 1800Hz by a 4060 chip,
gives the two frequency outputs required. These can be fed into an AND gate to
give the tag waveform, if a three input AND gate is used, a 555 chip can again
control shot length and auto-fire capabilities. This gives a stable gun circuit,
which will last many years of tagging. The first gun I built used such a circuit
and is still going strong after 8 years of fairly hard use.
Crystal Circuit:
With both of the above circuit ideas,
muzzle flash, sound effect and ammo counter/lockouts have to be added to comply
with the UK inter-club rules.
A third method uses a PIC to do all the
hard work of producing the tag waveform, single/auto shot, ammo counters etc,
all on one chip. It can also control a sound storage device such as the ISD2532
for sound effects, so, with the addition of a few components, a PIC based gun
board is really the option to go for. The PIC usually chosed by tag equipment
producers in the UK is Microchip Technology’s PIC16LC84, which is both cheap
& easily programmed.
For details of emitters available from
us, see the emitters section of this site.
Details on basic gun construction and
circuit details of a very good crystal based gun circuit can be found in the
"DIY construction guide & FAQ" section of Dave Bodger’s web site
at http://www.compulink.co.uk/~lasertag/lasertag.htm or
http://www.cix.co.uk/~lasertag/
The Sensor
The sensor is far more complex than the
gun:
Not only does it have to correctly sense
shots with the correct waveform, it also has to detect these signals through all
the interference put out by the sun, electric lights etc.
First of all it must reject all slowly
moving IR signals, such as the sun, then ignore all signals without a carrier
frequency of 57.6kHz, then filter out all signals that maybe oscillating at
57.6kHz but have no 1800Hz component. Once a signal has got through all that, it
is tested for pulse train length, that is counted by the sensor as a
"hit". This makes the sensor flash and beep and counts off a life,
once all lives are counted off, the sensor informs you that you’re dead or
unconscious.
