PSN-L Email List Message

Subject: Re: piezo-geophone
From: james fisher kd6iwd@.........
Date: Mon, 2 Jul 2001 13:36:05 -0700 (PDT)

jim fisher kd6iwd@.........
I made a seismic sensor out of a 1.5 inch piezo disk
transducer. In my application I was trying to detect
footsteps. I was able to detect footsteps at least 75
feet away. Piezo transducers may be suitable for
strong motion transducers or even as general purpose
geophones. I adapted the piezo disk to seismic use by
placing a 2# hammer head on the disk. The idea was
that as the seismic waves passed the disk would see a
varying load caused by the inertia of the hammer head.
I amplified the resulting signal with a simple op27
amplifier and viewed the output on a oscilliscope. I
was able to detect footsteps 75 feet away from the
transducer and cars at 2 blocks. If you try using
piezo disks be advised that they are very sensitive to
sound and to temperature changes which can cause large
dc voltages. The oscilliscope I used was an old tube
type and had a very bad ac hum problem. 75 feet was
the limit of the distance i could see the screen and
produce the seismic input. It might pick up footsteps
much further away with nouse free amplification and

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Larry Cochrane <cochrane@..............>