Indian Institute of Technology Hyderabad Vibration Detector

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 o Detecting & producing of sounds o Generating voltage o Microbalance o Ultrafine 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 )

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(Op- Amp).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.  V R 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.

AdvantagesDisadvantage  The piezo element can detect slightest vibrations to make it useful to detect seismic waves  Useful, cheap and can be used for many applications  It is difficult to monitor such a detector  Piezoelement loses its efficiency after certain period of time

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