
 
 
  \ \ \ \ \ \ \ \ \ \ \ \ \ \ 
 \[____________________________[_    \                                /
 \[      the chrome box        [_     a portable self-contained device
 \[        14-jun-88           [_    /  to manipulate traffic signals 
 \[   outlaw telecommandos     [_      /     by remote control       
 \[     modem free earth       [_           /                 
 \[\\\\\\\\\\\\\\[_                 -=p*p=-
   _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
 
   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, 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, ou 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.  orl 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.
 
  ome 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 ----->
 
 ******************************************************************
 * please add any new patterns or info you discover to this phile *
 ******************************************************************
 
 thanks to those who posted observations on the south bay wwiv's.
 
 
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