I have thought about it and thought about it and I have come to the conclusion the
   best way to do it is in hardware. The MC68HC908 does not have the additional timer
   needed to do it in software.

   This uses a CMOS 555 pulse width generator to generate a pules width that will delay
   a 3 ms one shot to fire LS1 coils and RX8 coils. These coils will overheat and fail
   if the dwell is much longer than 4 or 5 ms. I have tested all these circuits and the
   CMOS 555 pulse width generator works extremely well. Much better than my wildest
   expectations. It works the same way the 555 EFI system works.

   The RPM parameter is in the form of an analog voltage. In other word an analog tach.
   It is a simple circuit that generates a DC voltages when fed with a constant pulse
   width depending on the RPM. Basically a resister and capacitor.  High RPM more
   voltage low RPM less voltage.

   This is fed into the CMOS 555 to generate a varying pulse width delay. Low RPM long
   delay. High RPM short delay. Therefor the signal is reversed by an inverting op amp.
   The whole rig is triggered about 50 degrees BTDC.

   Here is the preliminary circuit.

   I'll do a bunch of tiny PC boards and sell them. You can buy the parts from digikey.

   Paul Lamar



 On 07/27/2012 08:00 AM, DIYAutoTune.com Sales (Matt) wrote:
   If you want to do something like this, you're on your own - I don't see it having any
   advantage over using the MS2/Extra dedicated spark control features. I don't really
   understand why you're doing this, and if you want my advice in the matter, I would
   recommend just going with the MS2/Extra rotary settings.

   Thanks,

   Matt Cramer

 MS2extra is way overkill for our purposes, way too complicated, with way too many add
 on/plug in cards and way too expensive. The MS 1 version 2.2 is perfect for our
 purposes except for the lack of ignition. Besides that the MS2 Extra is programed in
 C. C is not my cup of tea. I like to know exactly what the program is doing,
 precisely what it is doing and exactly how long the program takes to do it.
 I also takes a lot of time doing software and it is never bug free.

 This cheap circuit (less than $50 including the PCB) also works with carbs and LS1 or
 RX8 coils. It has adjustable dwell times and advance rate with out rewriting the
 software program.

 The attached pdf is the first documented embedded use of a single chip computer as
 far as I can find. If anybody can come up with one that was done and documented
 earlier I would like to know about it. I am not talking about home computer toys
 with keyboards and crt displays.

 BTW I have been on my own ever since I was 15 years old  in 1950 :)

 Paul Lamar

Pretty sweet Paul.  Based on a sweet little 6502 MPU.  I like it.

 Mark LaPierre

6502's were widely used to control NC mills among many other things,
I have one in my hangar. It was called a Bandit controller.

Paul Lamar
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