In a message dated 02/07/01, kd6iwd@......... writes:

> 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.

       For general purpose use, about 5 gm stuck to the centre with epoxy 
will give a resonance at about 500 Hz. Max safe load is ~100 gm. To stabilise 
the temperature adequately, you either need a very good thermostat or to bury 
them over 18" deep. A MAX420 / 430 or a TLC2201 are probably better 
amplifiers. It is a good idea to fit a pair of 5 pA catching diodes as these 
things can generate tens if not hundreds of volts. You can get disks of 50 nF 
capacity which give reasonably long TC's. Can be an advantage when 
experimenting / setting up if you put 100 K + a reed switch across the piezo 
unit to give rapid zeroing.

       Chris Chapman

In a message dated 02/07/01, kd6iwd@......... writes:



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.




       For general purpose use, about 5 gm stuck to the centre with epoxy 

will give a resonance at about 500 Hz. Max safe load is ~100 gm. To stabilise 

the temperature adequately, you either need a very good thermostat or to bury 

them over 18" deep. A MAX420 / 430 or a TLC2201 are probably better 

amplifiers. It is a good idea to fit a pair of 5 pA catching diodes as these 

things can generate tens if not hundreds of volts. You can get disks of 50 nF 

capacity which give reasonably long TC's. Can be an advantage when 

experimenting / setting up if you put 100 K + a reed switch across the piezo 

unit to give rapid zeroing.



       Chris Chapman