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 detection. __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail http://personal.mail.yahoo.com/ __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>