I was disassembling a defective half height  hard drive over the weekend
and had an interesting idea.  I was removing the platters and was down
to the magnet, coil and arm.  I thought, the only thing missing here to
make a seismometer is a weight at the end of that arm.  I put a car
wheel weight (about 100 gm) and sure enough, looking at a sound card
input, it is about the same sensitivity as my big vertical-at least from
1 hz to 40 hz.  It could just as easily be a vertical with a different
mounting and the addition of a spring.  The flexible circuit board that
connects to the VC on the boom arm is too stiff for good sensitivity but
it could be replaced by fine wire.  This may prove to be an interesting
project, I think it may be at least as sensitive as a geophone.  I still
need to do some work on the amplifier section, it's only half done.
Incidentally, I'm using LTC1063 digital 5 pole low pass filters for
filtration-anybody else ever use these?=20
=20
John Nelson





I was =
disassembling=20
a defective half height  hard drive over the weekend and had an =
interesting=20
idea.  I was removing the platters and was down to the magnet, coil =
and=20
arm.  I thought, the only thing missing here to make a seismometer =
is a=20
weight at the end of that arm.  I put a car wheel weight (about 100 =
gm) and=20
sure enough, looking at a sound card input, it is about the same =
sensitivity as=20
my big vertical-at least from 1 hz to 40 hz.  It could just as =
easily be a=20
vertical with a different mounting and the addition of a spring.  =
The=20
flexible circuit board that connects to the VC on the boom arm is too =
stiff for=20
good sensitivity but it could be replaced by fine wire.  This may =
prove to=20
be an interesting project, I think it may be at least as sensitive as a=20
geophone.  I still need to do some work on the amplifier section, =
it's only=20
half done.  Incidentally, I'm using LTC1063 digital 5 pole low pass =
filters=20
for filtration-anybody else ever use these? 
 
John=20
Nelson