I've got the task of repairing our 36 year old Foucault pendulum
display. A few years ago the campus electronic systems repair guys
ripped out the (completely functional) vacuum tube circuit to replace it
with a solid state circuit. They destroyed and discarded the old
circuit. Then the guy retired and said we give up, it's all yours. Sigh.
Thus, I no longer have any real clue as to the original sensing system
or power requirements for the big electromagnet ring.
All I really know is that the original sensors were a set of three
lever style contact switches that touched the cable when it swung.
I've started to design my own system using LEDs and photodiodes with a
simple logic circuit to trigger a timer to drive a power MOSFET to turn
on the magnet. When I built it on the bench it worked great. When I
installed it and connected it to the actual electromagnet it no longer
worked correctly (gets very unstable). I guessing that the larger amount
of inductance in the coil is feeding back into my circuit. (It is a real
effort to work with the actual system since it is up in a very tight
spot in the attic rafters and is hard to access comfortably. With
significant effort I've now yanked the ring out and have it on my bench
to test with the next circuit. The rest of the pendulum is welded
together in place and won't fit through the opening. It will have to be
worked on in the rafters.)
I'd rather not reinvent the wheel. I didn't have much luck with web
searches for circuits. Does anyone have a circuit they can share?
Thanks, John
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John E. Sohl, Ph.D.
Professor of Physics
Weber State University
2508 University Circle
Ogden, UT 84408-2508