[Gmecm] Interfacing HEI module to Pertronix pickup assembly

[David Allen]

  Okay. I found 2 circuit diagrams on the net, but they  have some problems.
One, keeps current on the coil all the time thus overheating the module and
coil when the engine is not turning.  The other fires on the FALLING edge of
the square-wave signal.  Not sure what this will do but that is not how the
Pertronix is timed.  Also, both these may or may not fire one random spark
when the ignition is turned on or off.  Not too good either.  Both these
operate by putting an extarnal voltage source on the P and N pickup coil
terminals through resistors and other components.  Supposedly they will work
but I am not happy with the side effects.
  I'm going to try the isolated circuit described below tomorrow.
  I would still like to hear if anyone else has successfully done this?
  Later,
David



>  Hey all.  I have to convert a distributor from points to ECM-controlled
> HEI ignition.  The distributor can not be modified to use a magnetic
> pickup coil.  It can, however be modified to use a Pertronix Ignitor
> pickup.
>  The Pertronix pickup provides a grounded signal suitable to drive an
> ignition coil directly.  I have to use this signal (firing event on rising
> edge of square wave pulses) to operate an HEI module.  What sort of
> interface circuit will work here?  I have a few ideas but I bet this has
> already been done by someone here on this list.
>  The Pertronix circuit, when used with a 100R pull-up resistor, produces a
> square wave that is lowest at 0.75 v and highest at battery voltage. The
> HEI module expects an isolated magnetic pickip coil.  I have an idea of
> using an op-amp comparitor circuit that switches at 1/2 battery voltage,
> driving a small isolation transformer that will give the HEI module it's
> signal on an isolated circuit.
>  I will draw a diagram later and post it.  Thanks for any input!
> Later,
> David