The circuit can also be used as a shield for microcontrollers, using appropriate power.




   The sensor of this circuit is a piezoelectric ceramic removed from a gas hob igniter. This ceramic must be positioned in such a way that vibrations in the vertical direction actuate it and on it must be placed a weight that will act as mass of pressure on the ceramic generating the signal for the circuit.

   The high gain operational amplifier as well as the components that polarize it must be mounted in a shielded box to avoid the noise pickup, since the circuit is extremely sensitive. The gain is given by a 100 M ohm feedback resistor and the capacitor in this same circuit as well as in series with the resistor connected to the (-) pin of the operation determines its frequency response to the very low frequency (infrasound) at which it is most of the signals to be detected.

   The instrument is a common 1 or 2 mA full scale microammeter. For better performance the diodes connected at the tip that drives this instrument should have low conduction voltage, such as germanium types. If possible, Schottky diodes will be even better. The circuit also has two indicator LEDs, and its power must be supplied with a symmetrical source.

   We can also apply the detected signals to an external recorder including an analog-to-digital converter (ADC) for registration on a computer. The consumption of the circuit is low, and its power can be made with batteries or battery.

   Equivalent operational amplifiers such as the CA3140 can be tried out in this circuit.



CI-1 - OPA124P - operational amplifier

D1 to D4-1N34 or Schottky diodes

LED1, LED2 - Common red LEDs (optional)


Resistors: (1/8 W, 5%)

R1, R2 - 100 M ohms

R3 - 2.2 M ohms

R4 - 47 k ohms

R5 - 100 M ohms

R6 - 2.2 k ohms

R7 -4.7 k ohms

P1 - 10 k ohms - trimpot



C1 - 10 nF x 400 V - ceramic

C2-22 pF-ceramic

C3 - 5.6 uF - polyester or electrolytic

C4 - 100 pF - ceramic

C5 - 5.6 uF - polyester or electrolytic



X1 - Piezoelectric ceramics - see text

M1 - 0-1 mA - mobile coil indicator

Printed circuit board, symmetrical source, wires, solder, etc.



N° of component