I have about decided to do a single chip solution to
   the dwell ignition problem  because  potentially it is the
   cheapest way to do a stand alone ignition for use with a carb.
   The knowledge gained can then be used to do a variety of simple
   things including a trim table adjustment to the 555 fuel injection
   system using spread sheet data as suggested by Henry Nee.

   I will focus on assembly language as these are time critical jobs
   and with assembly language you always know how long
   it takes to do anything. If you keep the job  short and
   simple the software size will be manageable from many aspects.

   Further more I have considerable experience with assembly
   language much of which can be applied to the AVR instruction
   set.

   I realize that most of you will not be interested so you
   can delete the messages on the subject.

   Those that wish to follow along can make a folder and move
   the stuff over to that.

   Tom Walter, I think, was the first to mention the
   Arduino board as a good low cost and small AVR trainer that will
   do a variety of jobs. The advantage is it is wired
   for USB and there is programming software that runs
   on both Windows and Linux.

   There are a lot of people using this board around the world so there
   should eventually be a lot of asm code examples.

   The Arduino Mega 2560 is a small microcontroller board based on
the   ATmega2560.   It has 54 digital input/output pins (of which 14
can be used as   PWM outputs), 16 analog inputs, 4 UARTs (hardware
serial ports), a 16 MHz   crystal oscillator, a USB connection, a
power jack, an ICSP header, and a   reset button. It contains
everything needed to support the   microcontroller;   simply connect
it to a computer with a USB cable.

   We will be using only a very few of these capabilities but the
cost   and size is so low it does not matter.

   AVRA is an assembler for Atmel AVR microcontrollers, and it is almost
   compatible with Atmel's own assembler AVRASM32.

   The initial version of AVRA was written by John Anders Haugum in
1999. He   released all versions until v0.7. All later versions were
released by   Tobias   Weber. And version 1.3.0 is released by Jerry
Jacobs.

   Paul Lamar

   Runs on a Mac too.  This is the board we are using in the Mechatronics
   courses at the University of Utah.  Mostly for automated robots
with lots   of sensors.

   Chris Cosman

  Paul,

  The AT90USB Demo-Kit sells for 31.00 on Digikey and I think
provides  similar resources, plus has some external flash storage
that might help for  storing tables.  Check it out, as it could be a
cheaper alternative.

  Thanks,
  Brannon

  That is a bargain. I had to call and confirm it was completely assembled.
  That beats the Arduino for our purposes. Thanks for finding that Brannon.
  I ordered one.

  Paul Lamar

Paul,

No problem, happy to help.  Let me know if you would like any help coding
this up or if you'd like someone to review your code.  I've done several
designs on these processors and one on this board in particular.

One note, you might want to consider writing the majority in C, as
you will be able to use the Atmel supplied libraries for USB
communication, etc, and coding your time critical procedures in
assembly.  Most compilers have statements that allow you to write in-
line assembly.  Also, you can always generate the .lst file on
compile and see what assembly is being generated for any code you do
write in C.

Thanks,
Brannon

Great Brannon!

Good to hear it. Here is the problem.
At 7500 RPM the engine makes one rev in 8 ms.

The RX8 coil delays a fixed  2 ms after the crank sensor tells
it to fire. This is called dwell.  In effect what this does is retard
or reduce the advance near 90 degrees. That causes the spark to fire
about 70 degrees AFTDC!!!!!! Of course losing power in the bargain
and hurting the BSFC. (fuel burn).

My suggestion is to measure the period of a given RPM and anticipate
the advance required up to 2 ms at 7500 RPM for the next revolution.
As you go through the rev range of course the adjustment changes. No
adjustment at idle and a lot
(2ms) at 7500 RPM.

Any ideas? Do you have a scope you can test it with?

CD's don't do this but they are a lot of bucks compared
to the LS1 or RX8 coils with built in solid state switches.

Paul Lamar


Automotive computer ignitions use the previous CAS signal to fire the plug
you want. It is easy to delay the firing event, but anticipate it? What could
be used is the adjustable pick-up mounting and a timing light to find where it
needs the pick-ups to be to get the advance required. Once the position is
determined for the set-up, the rest should be close with a small adjustment
like setting timing on the distributor.

Dale Davies

Well if you measure the time it took to rev the engine once
and subtracted 2 ms when you  fired on the next rev I think that would
work.


Paul Lamar