Paul,

   I have tested this already- if you have the stock (old style) coils
   with ignitors here is what you need to make spark:

   1.The VR boards that we emailed back and forth about earlier-
   http://www.jbperf.com/dual_VR/v2_1.html. One board is good for 2 CAS
   pickups- you would need 2.
   2. A board with 2 7805 voltage regulator chips and 3 FET transistors.
   The stock CAS generates the rising/falling signal to the VR board,
   the VR board takes the 5v input signal and pipes a single 5v pulse
   to the transistor, which turns on and allows the 5v signal to
   trigger the coils. The 5v signal from the VR board should trigger
   the coil to fire, but I would offload any current and possible
   flyback to a separate board, and maybe add a flyback diode in there
   just in case something goes wrong :).

   If you have newer coils, just trigger the coils off of the FETs, and
   leave the other the same. The VR board comes in an external
   regulated and internally regulated version- the internally regulated
   version has the regulator built in and will work off of the 12v system.

   If you have the coils, the boards are around $30.00.

   KevinA


   Kevin, do the VR boards send a narrow negative pulse to the smart coils?
   If so the smart coils are conducting current all the time except for
   the pulse width.
   The LS1 and RX8 coils have both overheated and failed.

   In the old days that's how distributors worked. The coils were on
   most of the time.
   When the points opened the coil fired. If you turned on the ign with
   out starting the
   car the coils some times would get hot enough to burn your fingers
   but they were
   in a steel can filled with oil. That assumes the points where closed.

   One of the things you can do is use a 4 ms wide 555 one shot
   negative pulse. That way
   the coil is only on 50% of the time at 8000 RPM (roughly) and 75% of
   the time
   at 4000 RPM  and 87.5% at 2000 RPM idle.

   Paul Lamar


   The Variable Reluctance boards take the (rising I think) signal from
   the CAS and use it to trigger a short 5v pulse out. This pulse out
   can either turn on a transistor i.e. PNP and drive the coil, or sink
   the coil signal to ground i.e. NPN.  The board only has a single
   simple function- take the variable voltage/capacitance (reluctance)
   rising/ falling peak signal from the CAS and convert it to a single
   5v pulse. The coils that I have are the built in ignitor ones, that
   are connected to 12v, with a 5v trigger. I tested the coils with the
   VR boards and the CAS up to 3000 engine RPM (1500 rpm drill) and
   with a board simulating 7500 RPM. The coils fired throughout the
   range flawlessly. My only issue now with the coils is my discussion
   with Fred about the coil unit not being able to reliably fire 2
   plugs at once since one side is wasted spark and shouldn't be firing.

   The web page for JB Performance tells which part of the signal it
   uses to produce the ignition signal. I wouldn't think it would be
   important other than it would change the timing a slight amount from
   one to the other.

   My interest in these boards came from 1. reading the Megasquirt
   boards and seeing the problems that a VR CAS causes in the
   computers, 2. talking with Fred with FREEems about the same issue,
   and 3. wanting a reliable way to fire the coils in the event of
   complete ECU failure. This simple little board does that. You could
   also build the board using an LM1815 chip, but this chip is a
   through hole, and makes the unit way bigger. This thing is about as
   big as a nickel.

   My testing indicates that with the timing set at 22 deg BTDC, and
   using these chips and the transistors, I can reliably fire the coils
   on minimal power. Add in a mechanical/ manual fuel source and you
   have a mechanical backup that will get you home, or at least to a
   better landing area. I will do more testing as I get this second
   plane done and get back to my first one with the 13b.


   KA

   Well then the coils are subject to over heat as it must be a
   negative going pulse to trigger.
   Unless there is a one shot in there the pulse width will be less
   than one ms. Probably only
   a few microseconds. Do you have a O scope? This is worse than a
   distributor with points.
   The "T" indicates a plug fire.

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   If it was a positive going pulse it would have to be longer than 4
   ms to give the coils time to
   charge or it would not work. That also involves a 555 chip.
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   Tracy went through a bunch of LS1 coils. He wound up with the the
   truck version with heat sinks and
     elaborate enclosed cooling system. I built a heat sink for the
   RX8. All this is the sledge hammer approach
   to the problem. The best thing is turn them on for 4 ms and turn
   them off to fire. The max on
   time is then 50% at 8000 RPM and  25% at 4000 RPM and much less at
   idle. Way less current at cruise.

   This reduces the current drain and gives you more time in case of a
   alt charging failure.

   Paul Lamar

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