Andrew Warren wrote:

> If you DO decide to do this project, though, I can offer a bit of
> advice:  Do all your testing on the bench, with a function generator
> replacing the car's distributor.  Spark timing that's bad enough to
> cause detonation will kill an engine fast, and timing that's GROSSLY
> wrong will kill an engine REAL fast.

Good advice.

Many a night, 'the shed' lit up due to carby and exhaust 'explosions'.
Couldn't believe the PIC survived all the crap it had to put up with.
Still got it somewhere.

Keep naked working spark plugs away from the PIC too. It will start
executing it's code upside down and backwards at the same time. Same
goes for old copper cored spark leads. Very frustrating to find bugs if
you are unaware of this.

Avoid ground loops through the PIC PCB. If the coil (or other) suddenly
decides to return it's current back through the PCB's ground due to a
faulty connection, the PCB will light up "Eat at Joe's" for a split
second then spit the dummy. I've seen it happen twice now.

Make your circuit robust enough for a brown out situation, such as
cranking with a half flat battery, and things such as load dumps etc.
Sometimes the PIC can fire up or run in an erratic manner.

One good thing about using a distributor with a 'home made' ignition
system is that you can bypass the PIC circuit and connect the coil back
up to the points to get home if something fails.

The 8 bit timers in the PIC are not really set up for high revving
accuracy. I think Motorola (are you allowed to say that here), have
purpose built processors for ignition control, whether or not you can
get them is another matter.

I did some rough math awhile ago, and on older slow revving motors,
using the distributor for a timing reference doesn't matter too much. Hi
performance, Hi RPM is a totally different ball game though. Best left
to the experts.

I think one of the trickiest things is getting control of the engine
just when you are starting to crank it. And then
there's...and...and...and..

As Andy said, "a project like this is harder than it first appears".

--
Best regards

Tony

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