Mike Montalvo wrote:
>
> There is a lot of ringing on the line.  There are also a lot of transients.
> I strongly suggest you use an opto-isolator. I have used them in the past
> for the same purpose with great success.  Get one with a Schmidt trigger
> output.

It sounds like the first ringing pulse that doubles the
frequency. He could use a debounce time slightly shorter
than the minimum firing time (highest revs) to take it out.

Some real protection on that pin will also be useful...

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