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
<http://www.jbperf.com/dual_VR/__v2_1.html>
<http://www.jbperf.com/dual___VR/v2_1.html
<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.

______________ _____________________________
......................||
......................T__|


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.
............................._______

.............................|   |
__________________|   T_______



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



"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 definitely would require a computer- the occurrence of the turning
on of the coil for charging would be RPM dependent- you couldn't turn it
on at an arbitrary angle before TDC, as we know this will vary from just
before the 22 degrees to as much as 180 degrees depending on RPM. So,
the computer would have to read the RPM and then adjust the charging
point based on calculating the ms before it needs to fire. The system
would always be behind, adjusting the charging cycle based on an RPM
that was read some time before. Since it is impossible to adjust
something to be correct now in a constantly changing system when your
data is based on an event that has already come and gone, the system
would always suffer from either weak spark or overheated coils. It would
only be optimal if the RPM was constant, which is almost an
impossibility. I know that we set a cruise speed and try to keep it
there, but every altitude change up or down changes the RPM a little.

In theory, the computer could read the RPM and send a pulse to a
transistor at the right time that would charge the coil, but as I said
above, that would be like driving by looking out the rear view mirror.
If the pulse was exactly 4ms, then when it would be applied would have
to be the result of an RPM read, then read the CAS for crank angle
position, calculate the moment needed, and fire.

Something is missing- I need to read more.

Kevin Alderman

A peice of cake for a Radio Shack Arduino.
$20 on ebay.
http://www.arduino.cc/


This has been on going problem for years.
The trick is set the trigger pulse early enough to give
the computer time, based on RPM, to turn the coil on and then off
to fire the plug. You will need an RPM input.

Make it stand alone separate from the fuel injection.

You would do us all a big favor if you wrote the software
and published it on here. I am not a fan of Arduino code and
I am trying to focus on the turbo compound.

It would work with LS1 and RX8 coils.

Paul Lamar