"Steve Lusardi" fired this volley in
:

Tom,
Switches are a non-starter. You will never get the cycle rates you are
looking for. I suggest you keep it simple and stick to hall effect
sensors, amplifier and a solid state switch.

I'd like to suggest an alternative. Hall Effect sensors work reliably,
but they're difficult to use in a mechanism requiring as tight an off-to-
on angle of rotation as he requires. They're better for things like
sensing rotation speed, or locating a position that's not so critical as
Tom requires.

The alternative, and one that works well in millions (yes millions) of
consumer machines, that works in hostile, hot, dirty environments; that
can sense angles as small as 1/10th degree easily, and can easily be made
to have adjustable dwell is: A controlled-reluctance sensor.

Pole width determines positional accuracy. Dwell can be established by
distance to the sensed cam or by electronic means.

The cost is a bit more than Hall Effect types, because you'll require
more electronics to sense and condition the signal. But it's minimal
compared to the advantages they offer.

Just because you have a dirty environment doesn't rule out the use of
optical choppers. Proper positioning can keep them clean in most
applications. And they're the simplest of all types, providing all the
features Tom wants without any complex 'tronix.

LLoyd