🚀 go-pugleaf

Gateway Electronics in San Jose had some used seismic sensors.  I got
one but haven't had time to play with it.  I think it's a heavy metal
shell with a moving coil inside - kinda like a speaker.  There is a
threaded fitting (about 3/8") on one end.  The whole thing is about 1.5"
in diameter by 2.5" long.  I suspect they are removed from military 
surplus something or other.  You get a copy of a little op-amp circuit
with it which includes, among other things, a comparator to switch an
output if the detected seismic amplitude is above a certain level.  Maybe
these were used in land-mines :-)


	-Paul Bame