The
piezoelectric element of a kitchen gas lighter is used in this simple,
yet effective seismic detector. The piezo element must be placed
vertically, one end solidly to ground. A 2-3 pound weight of fine gravel
in a loose package should be placed on top at the other end. The high
voltage lead goes to the IC, placed close to the piezo element. The
whole box is acoustically and electromagnetically screened. A 3 core
shielded cable brings the signal to the rest of the circuit and to the
power supply (+/- 15V). The SB140 diodes are Schottky type and pin 8
(substrate) of the IC should be connected to ground.
