If you look at post #24 circuit that the OP is using, I am not satisfied with some of the component values/timings also the description on how the circuit works.
I originally tried in another posting, to utilize the fact that
the coil produces voltage when induced, but nobody could
direct me how to integrate that into making the servo move.
I happened to series it into the circuit, and believe it or not,
with a few weeks of refinement, it actually does work. I can
pick up cars driving by in the parking lot, and neighbors when
they walk across the floor in adjacent apartments. This is SO
much more than I managed to get by attempting amplification
of the coil's voltage. I just know it does work, and it is VERY
sensitive (it actually moves when the A/C runs and I don't
have the pendulum/magnet/coil enclosed, simply due to airflow).
This part of the circuit is done. I don't actually work for the
USGS anyways, so having the stylus draw a 1/4" line when a
car drives by or a neighbor walks around on my floor, is more
than acceptable (considering the last quake we had here moved
pictures on the walls!). I simply wish to get a heads up (via the
meter), when activity is about to begin...
https://www.electro-tech-online.com/threads/control-a-servo-by-a-small-voltage-signal.99716/