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Vibration Detector
Indian Institute of Technology
Hyderabad
Basic Principle
 The basic principle used in this setup is piezoelectricity.
 It is a phenomenon of internal accumulation of charge
in crystals in response to external mechanical force
applied on it.
:source(Wikipedia)
Applications of piezoelectricity
oDetecting & producing of sounds
oGenerating voltage
oMicrobalance
oUltrafine focusing of optical assemblies
Material used:
The material used in piezoelectric element is lead zirconate
crystal.
These crystals generate measurable piezoelectricity when
they are deformed
about 0.1% of their original dimensions.
These crystals readily release the current when the orientation
of crystal is disturbed by mechanical vibrations.
These signals are in turn given to IC 741 (Op-Amp)
Material used
 Op-Amp has two terminals
 V+ (non-inverting) input &
 V-(inverting) input
 OpAmp is a difference amplifier so it amplifies
difference between the inputs
 Even if the difference is small the output can
be as high as supply voltage(Vs)
 Negative feedback is given to V- so as to make
it a non inverting amplifier
 Open loop gain of OpAmp is very high (nearly
100000)
NPN transistor
 NPN transistor is used as a switch in this circuit
 When the base voltage is high the current in emitter and collector
increases
 Collector voltage will drop because of load resistance
 This will act as a switch to trigger signals to IC 555 (timer IC)
Mechanism:
 These signals are in turn given to an Operational Amplifier(OpAmp).The Op-Amp amplifies the current signal which in turn
gives high output .
 This high output from Op-Amp in turn will switch on NPN
transistor and it will start conducting.
Mechanism
 When transistor conducts, it will trigger pin 2 of
IC555(monostable multivibrator).
 IC555 will give high output to pin 3.
 VR is used to adjust the sensitivity of the piezo
element.
 This element is kept in a metal box which will be buried
inside the soil to detect seismeic vibrations.
Advantages
 The piezo element can
detect slightest vibrations
to make it useful to
detect seismic waves
 Useful, cheap and can
be used for many
applications
Disadvantage
 It is difficult to monitor
such a detector
 Piezoelement loses its
efficiency after certain
period of time
THANK YOU
Indian Institute of Technology
Hyderabad