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chrome.txt
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1998-07-29
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6KB
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143 lines
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CHROME BOX
----------
------------
Introduction
------------
Emergency vehicles in many cities are now using devices called
OptoComs. OptoComs are a system of sensors on traffic lights
that detect a pattern of flashes from vehicle-mounted strobe
lights.
This flash pattern varies from city to city depending on the
manufacturer of the equipment used. Often the sensors are in-
stalled only at major intersections. Nevertheless, the Chrome
Box, which simulates these strobe patterns can often be used to
give your car the same priority as an ambulance, paramedic van,
firetruck or police car.
Because of the varying patterns on different systems this phile
will outline a general procedure for making the Chrome Box.
-----------------------
Decoding Flash Patterns
-----------------------
First, you need to observe an emergency vehicle in action. You
can wait until you encounter one by chance, running out to see
when you hear a siren, or when you pull over in your car to let
one pass by. You might wait near a fire station for the next em-
ergency to occur. Or, if you are very impatient, you can summon
one by calling in a false alarm (not recommended in areas with
limited services - that could divert attention from a real emer-
gency). If the OptoComs in your area are the kind with a pattern
of single flashes at a steady rhythm, you have merely to buy a
strobe light at Radio Shack & adjust the flash rate until you can
induce a traffic light to change.
If the flash pattern is more complex, you can videotape the emer-
gency vehicle & then play back the tape in single-frame mode,
counting the number of frames between each flash. Each video
frame is 1/30 of a second, using this you can calculate the time
between flashes in the pattern. Another way is to count the
number of flashes (or flash-groups) in one minute and use that to
compute the rate. Counting video frames will give you a good idea
of the spacing of the flashes in a complex pattern. For really
accurate information, call the fire station & ask them, or write
to the manufacturer for a service manual, which will include a
schematic diagram that you can use to build one. A good cover
story for this is that you are a consultant & one of your clients
asked you to evaluate Optocom systems, or you could pose as a
free-lance journalist writing an article.
--------------------------
Modifying the Strobe Light
--------------------------
You may not have to modify the strobe at all. But if you need a
faster flash rate than your strobe allows, open it up & find the
large capacitor inside. Capacitors are marked in microfarads, ab-
breviated as mf,mfd or ufd. By replacing the capacitor with one
of the same voltage-rating (usually 250 volts or more) and a
SMALLER value in microfarads, you can increase the flash rate.
Halving the microfarads doubles the rate.
The other component that can be changed is the potentiometer (the
speed control device with the knob on it). Using a smaller value
(measured in ohms or Kilohms, abbrevaited with the greek letter
'omega' or the letter K) will speed up the strobe. There may also
be a resistor (small cylinder with several colored stripes on it,
and wires coming out of each end). Replacing this resistor with
one of smaller value will also speed up the strobe.
To generate a complex pattern, you will either have to design and
build a triggering circuit using IC chips, or rig up a mechanical
device with a multiple-contact rotary switch and a motor. It HAS
been done.
To modify the strobe for mobile operation the simplest thing is
to get a 110-volt inverter that will run off of a car battery by
plugging into the cigarette lighter & run the strobe from that.
Or, you can figure out (or find in a hobby electronics magazine)
a strobe circuit that will run from batteries.
Battery-powered strobes may also be availble, either assembled or
as kits.
------------------
Stealth Technology
------------------
Most light sensors and photocells are more sensitive in the in-
frared area of the light spectrum. Infrared (IR) is invisible to
the human eye. Putting an infrared filter over the strobe light
may allow the Chrome Box to operate in traffic undetected by pol-
ice or other observers. IR filters can be obtained from military
surplus sniperscope illuminators, or from optical supply houses
like Dow-Corning or Edmunds Scientific Co.
-----
Usage
-----
Mounted on your car, the Chrome Box can guarantee you green
lights at major intersections in cities that have OptoComs. Han-
dheld Chrome Boxes may be used to create gridlock by interfering
with the normal flow of traffic. If you have access to a window
overlooking a traffic light, you can play pranks by switching the
signals at inappropriate moments, or you can plug the strobe into
an exposed outlet at a laundromat or gas station.
---------------------
Some Decoded Patterns
---------------------
Torrance, California
Standard large Radio Shack strobe lights are used.
Moderately fast rate.
* * * * * * * *
Manhattan Beach,CA
Flash-pairs in a 4:1 ratio, at a rate of 2 flash-pairs p/sec
* * * * * * * *
<------ 1 sec ----->
+++EOF