> Michael Rigby-Jones wrote:

> The trouble with the
> software only approach is that you have to complete all calculations
> and keep a pretty accurate counter in between firing cycles.

Not neccessarily.

The last software I wrote precalculated a set of variables and these are
used at run time - virtually no math while running. The data is then
available exactly when needed. As I mentioned earlier, I can keep track
of RPM, pos or neg advance, vac adv, dwell and rev limit in about 50
instructions. That is about 25uS @ 8MHz, but it still becomes an issue
at high RPM.

To test the software, I had two signal generators running. One at 500RPM
and another about 6000RPM simulating the timing for a V8. I used a
switch to change signals and as far as I could see the PIC coped OK. I
didn't have a storage CRO to see the changeover glitch though. On the
test bench the PIC could run a single 4 stroke upto 35,000 RPM.

The system has been quite popular with old car enthusiasts because of
hard to find distributor parts, and with people running engines on gas
because 2 data sets can be stored and changed over even when the engine
is running.

I have had ideas on doing another one with more features, but the time
it takes for development to cover a reasonable spectrum of
engines.....oooh the pain. The last time I was 'playing' with this idea
I was using a 16C74 and I could change the timing parameters even while
the engine was running.

There are four basic things needed to make a system work.

  Good programmer
  Electronics wiz
  Someone who knows engines inside and out.
  Time, time and more time.

Even so, it was probably one of the most interesting projects I have
done. Not too bad when you consider the whole shebang used only 1021
words of ROM.

--
Best regards

Tony

http://www.picnpoke.com
mailto:sales@picnpoke.com