I was surprised at the size of the capacitors
  so that added a bit of square inches to the
  PC board. Back in the old days (60's) we used
  large metal can capacitors that were oil filled
  for our CD systems and vac tubes of course.

  Those caps store the spark energy instead of
  being stored in the coils. CD coils
  run cool as they are simply used as pulse
  transformers.

  Boards cost about 65 cents per square inch
  Plus a fixed cost of $55 for tooling.

  The caps are the 4 big boxes in the center of the PC
  Board. I'll use my favorite heat sink and
  TV connector for the output to the coil.
  This is for one spark plug on one rotor.
  The trailing plug does not need it and
  and any back up ignition can be used on the
  trailing rotor.

  This requires 4 Hall Effect devices
  per plug to trigger every 10 degrees for
  40 degrees after 22 degrees BTDC.
  In other words 20 BTDC, 10 BTDC, TDC and
  10 degrees after TDC with no RPM limit
  such as MSD's have problems with.
  One cap for each spark.

  The whole idea here is to see if it will
  cut the fuel burn.

  I'll see if I can get Mazdatrix to test it on
  the dyno. I'll loan it to them for use on
  what ever engine they are fooling with at
  the moment.

  It uses one 400 watt 220 Volt AC off the shelf 12 V power
  supply for up to 6 PC boards if you want to implement
  that many on a 3 rotor.

  Paul Lamar

 It would appear that isolation devices are needed between the four 2mfd
 caps and the coil.  When trigger is low, there is a low impedance to
 ground thru the lower FET of the half-bridge, essentially putting the
 caps of the untriggered drivers in parallel with the coil.

  Victor Roberts,

 Yes I see what you are saying. It is helpful I have
 other engineers looking over my shoulder.

 I need some more switches in there.
 Thanks Victor. Do you have any suggested circuits?

 Paul Lamar


I would use two diodes for each circuit. Insert a diode between each cap
and the coil, and a diode from the junction of the cap and diode to
ground.  See the attached .pdf.  Each cap gets a pair of diodes.  Sorry
about the puny sketch but I;m having to remote control the software over
a slow connection while on vacation, and my grandsons are nagging me to
go outside with them.

Victor. That looks like it will work.

Thanks Victor. I'll try it.

Paul Lamar