Just to muddy the waters,
The system Trevor is describing is a reluctor system,
where the coil picks up the field transision ( notice the
metal wheel with the little nubs sticking out that go
by the coil). A Hall effect system uses a Hall Effect
transistor to detect the magnetic field reversals, not a
coil. The Hall effect transistor has a highly doped gate
that controls the emitter/collect currect based on the
strength of the magnetic field in the gate area ( it
directly senses the field). Dr. Hall of course is the one
who discoved the effect while working on transistor
development. Kind of the same princple, just a different
senseing device.
Harlan.
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