IVP wrote:
> The only thing that makes some difference is the
> orientation of the board wrt the spark plug. A metal case helps a
> little but it still happens occassionally
>
> I'm wondering if the noise is so great from the spark plug that it
> actually gets into the body (DIP8)

Far more likely is that the EMP caused by the spark is causing voltage
offsets acrross the board.  This is a case where careful consideration of
ground layout, ground currents, and other loop currents is very important.
Fortunately the same things you do to design for low emission work to make
the system less susceptible to received radiation.

Show the layout.  That's where the problem will be.


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