What kind of RPM are you looking at?  Model aero engines generaly ren much
higher than car engines.  Tony Nixons software at http://www.picnpoke.com
shows the general idea and is very cleverly written.  However, if your
engine revs susbstantially higher than the few thousand RPM this software
can deal with, I think you are going to have a hard time getting reasonable
resolution just through software timing loops.  Using a PIC with
capture/compare hardware (which the 16F84 does not have) would ease timing
constraints on the software.

Hmm maybe the recent overclocking thread could be usefull here!


Mike Rigby-Jones
mrjones@nortelnetworks.com


> ----------
> From:         Andrew Schenk[SMTP:ASchenk@ATI.STLAWRENCEC.ON.CA]
> Sent:         10 February 1999 22:19
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Using PICs to control Spark Ignition
>
> Has anybody ever tried using a PIC to control a spark ignition system.
> Than
> plan is to sense the propeller RPM on a 2 stroke gasoline engine from a
> radio controlled modelairplane. Depending on the RPM, the spark will be
> advanced. for a prototype, the 16F84 will be used. The input will probably
> be an optical sensor as engine weight is a concern. A magnet in the fly
> wheel would add to the weight. What I am not sure about is the conversion
> from a radian numerical value to a delay time for the spark.
>
> Thanks
> Andrew
> Student of Instrumentation Technology
> St. Lawrence College
> Kingston, ON CANADA
>