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 give 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