> Don Harris wrote:
>
> Any of you have experience with timeing advance for a gasoline
> engine.  I have a hall affect pickup on the prop hub for a
> model airplane engine, and will us this to trigger the
> appropriate delay for the spark. The pic will accecpt
> the hall affect input and initiate the appropriate delay
> (based on RPM), and then output a pulse to trigger a
> capacitive discharge ignition.  I have designed the CD
> but need help with programming the pic (12cxx 8 pin). I
> am an electronics tech but could probably modifiy code
> to suit my application  if there is an example out there.
> Does not have to be for the 12cxx chip.


Many years ago in my dim and dark past I worked on a
project with two friends to build an endurance RC plane.
We converted a glow engine for spark ignition. The pickup
we used was capacitive. We replaced the back
prop washer with a disk that had a hole filled with
epoxy that gave an abrupt change in the effective capacitance
between the disk and a non contact pickup. The ignition
system was a small CD system. The electronics took the
throttle servo control signal to control the spark
advance.

We spent a lot of time getting the electrical noise down
to reduce radio interference. In the end this was not a
problem so I suspect the processor would not be a problem.

If I had to do it again I think I would decode the throttle
signal with the processor and have the processor drive the
throttle servo. That way the processor can use the throttle
signal as a setpoint in a control system. The processor can
measure RPM, setpoint and control spark advance and throttle
position.

Walter Banks
http://www.bytecraft.com

PS The plane flew a little over 8 and half hours.