textfiles/phreak/BOXES/chrome

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<EFBFBD><EFBFBD>      The Chrome Box        <20><>     A Portable Self-Contained Device
<EFBFBD><EFBFBD>        14-JUN-88           <20><>    /  to Manipulate Traffic Signals \
<EFBFBD><EFBFBD>   Outlaw Telecommandos     <20><>      /     by Remote Control       \
<EFBFBD><EFBFBD>     Modem Free Earth       <20><>           /                 \
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  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 installed 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 emergency 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 emergency).  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 emergency 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, abbreviated 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, abbreviated 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 infrared 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 police 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.

Using the Chrome Box:

 Mounted on your car, the Chrome Box can guarantee you green lights at
major intersections in cities that have OptoComs.
 Handheld 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 per second.
   * *       * *       * *       * *    
   <------ 1 sec ----->