Design And Implementation Of Seismic Sensor 6k3p5i

DESIGN AND IMPLEMENTATION OF SEISMIC SENSOR

by

LINUS ANTONIO OFORI-AGYEKUM EMMANUEL AFFUM AMPOMMA [email protected] ELECTRONICS AND COMMUNICATION ENGINEERING

ALL NATIONS UNIVERSITY COLLEGE KOFORIDUA

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CHAPTER ONE INTRODUCTION 1.1 Overview There are two basic types of seismic sensors: inertial seismometers which measure ground motion relative to an inertial reference (a suspended mass), and strainmeters or extensometers which measure the motion of one point of the ground relative to another. Since the motion of the ground relative to an inertial reference is in most cases much larger than the differential motion within a vault of reasonable dimensions, inertial seismometers are generally more sensitive to earthquake signals. However, at very low frequencies it becomes increasingly difficult to maintain an inertial reference, and for the observation of low-order free oscillations of the Earth, tidal motions, and quasi-static deformations, strainmeters may outperform inertial seismometers. Strainmeters are conceptually simpler than inertial seismometers although their technical realization and installation may be more difficult. An inertial seismometer converts ground motion into an electric signal but its properties cannot be described by a single scale factor, such as output volts per

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millimeter of ground motion. The response of a seismometer to ground motion depends not only on the amplitude of the ground motion (how large it is) but also on its time scale (how sudden it is). This is because the seismic mass has to be kept in place by a mechanical or electromagnetic restoring force. When the ground motion is slow, the mass will move with the rest of the instrument, and the output signal for a given ground motion will therefore be smaller. The system is thus a high- filter for the ground displacement. This must be taken into when the ground motion is reconstructed from the recorded signal, and is the reason why we have to go to some length in discussing the dynamic transfer properties of seismometers.

The dynamic behavior of a seismograph system within its linear range can, like that of any linear time-invariant (LTI) system, be described with the same degree of completeness in four different ways: by a linear differential equation, the Laplace transfer function, the complex frequency response, or the impulse response of the system. The first two are usually obtained by a mathematical analysis of the physical system (the hardware). The latter two are directly related to certain calibration procedures and can therefore be determined from calibration experiments where the system is considered as a “black box” (this is sometimes called an identification procedure). However, since all four are mathematically 3|Design &Implementation Of Seismic Sensor

equivalent, we can derive each of them either from knowledge of the physical components of the system or from a calibration experiment. The mutual relations between the “time-domain” and “frequency-domain”. Practically, the mathematical description of a seismometer is limited to a certain bandwidth of frequencies that should at least include the bandwidth of seismic signals. Within this limit then any of the four representations describe the system's response to arbitrary input signals completely and unambiguously. The viewpoint from which they differ is how efficiently and accurately they can be implemented in different signal-processing procedures.

In digital signal processing, seismic sensors are often represented with other methods that are efficient and accurate but not mathematically exact, such as recursive (IIR) filters. Digital signal processing is however beyond the scope of this section. A wealth of textbooks is available both on analog and digital signal processing, for example Oppenheim and Willsky (1983) for analog processing, Oppenheim and Schafer (1975) for digital processing, and Scherbaum (1996) for seismological applications.

1.2 Literature Review

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As indicated earlier on, the most commonly used description of a seismograph response in the classical observatory practice has been the “magnification curve”, i.e. the frequency-dependent magnification of the ground motion. Mathematically this is the modulus (absolute value) of the complex frequency response, usually called the amplitude response. It specifies the steady-state harmonic responsivity (amplification, magnification, conversion factor) of the seismograph as a function of frequency. However, for the correct interpretation of seismograms, also the phase response of the recording system must be known. It can in principle be calculated from the amplitude response, but is normally specified separately, or derived together with the amplitude response from the mathematically more elegant description of the system by its complex transfer function or its complex frequency response.

While for a purely electrical filter it is usually clear what the amplitude response is - a dimensionless factor by which the amplitude of a sinusoidal input signal must be multiplied to obtain the associated output signal - the situation is not always as clear for seismometers because different authors may prefer to measure the input signal (the ground motion) in different ways: as a displacement, a velocity, or an acceleration. Both the physical dimension and the mathematical form of the transfer function depend on the definition of the input signal, and one must 5|Design &Implementation Of Seismic Sensor

sometimes guess from the physical dimension to what sort of input signal it applies. The output signal, traditionally a needle deflection, is now normally a voltage, a current, or a number of counts.

Calibrating a seismograph means measuring (and sometimes adjusting) its transfer properties and expressing them as a complex frequency response or one of its mathematical equivalents. For most applications the result must be available as parameters of a mathematical formula, not as raw data; so determining parameters by fitting a theoretical curve of known shape to the data is usually part of the procedure. Practically, seismometers are calibrated in two steps.

The first step is an electrical calibration in which the seismic mass is excited with an electromagnetic force. Most seismometers have a built-in calibration coil that can be connected to an external signal generator for this purpose. Usually the response of the system to different sinusoidal signals at frequencies across the system's band, to impulses, or to arbitrary broadband signals is observed while the absolute magnification or gain remains unknown. For the exact calibration of sensors with a large dynamic range such as those employed in modern seismograph systems, the latter method is most appropriate.

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1.3 Project Organization This project work presented the design and implementation of seismic sensors for industrial and domestic purpose using the piezo element and a piezo buzzer with its underlining principle of piezoelectricity. The circuit uses readily available components and the design is straight forward. A standard piezo sensor is used to detect vibrations/sounds due to pressure changes. The piezo element acts as a small capacitor having a capacitance of a few nanofarads. Like a capacitor, it can store charge when a potential is applied to its terminals. It discharges through VR1, when it is disturbed. The project work is organized as follows: chapter two will concentrate on the hardware description which is most importantly the TL071 JFET op-amp and the NE555 timer ICs while chapter three looks at piezoelectricity in details. Chapter four focuses on the design and implementation of the seismic sensor for both industrial and domestic application with piezoelectricity with detailed explanation of the project topic in general as chapter five concludes the project work.

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CHAPTER TWO HARDWARE DESCRIPTION 2.1 Introduction This chapter will focus on the features of the TL071 Low noise JFET single operational amplifier such as its description, electrical characteristics and its operations, and further look also at the NE555 Timer IC such as its overview, pin outs, pin descriptions, operating overview, electrical/environmental characteristics and monostable and astable operations. 2.2 TL071Low Noise JFET Single Operational Amplifier 2.2.1Description The TL071 is a high-speed JFET input single operational amplifier. This JFET input operational amplifier incorporates well matched, high-voltage JFET and bipolar transistors in a monolithic integrated circuit. The device features high slew rates, low input bias and offset currents, and low offset voltage temperature

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coefficient. The diagrams below show the pin out configuration and can package of the IC

(a)

(b)

Fig 2.1 (a) can package of TL071 IC, (b) pin connection of Tl071 IC The following are the description of the individual pin connections of the above IC as shown in figure 2.1. 1 - Offset null 1 2 - Inverting input 3 - Non-inverting input 4 - VCC5 - Offset null 2 9|Design &Implementation Of Seismic Sensor

6 - Output 7 - VCC+ 8 - N.C. 2.2.2Features of TL071 IC Tl071 IC is a slightly for powerful JFET single input operational amplifier which has the following features; • Wide common-mode (up to VCC+) and differential voltage range • Low input bias and offset current • Low noise en = 15nV/ √Hz •

Output short-circuit protection

• High input impedance JFET input stage • Low harmonic distortion: 0.01% • Internal frequency compensation •

Latch-up free operation

• High slew rate: 16V /µs

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All voltage values, except differential voltage, are with respect to the zero reference level (ground) of the supply voltages where the zero reference level is the midpoint between VCC+ and VCC. The magnitude of the input voltage must never exceed the magnitude of the supply voltage or 15 volts, whichever is less. Differential voltages are the non-inverting input terminal with respect to the inverting input terminal. Short-circuits can cause excessive heating. Destructive dissipation can result from simultaneous short-circuits on all amplifiers. Rth are typical values. The output may be shorted to ground or to either supply. Temperature and/or supply voltages must be limited to ensure that the dissipation rating is not exceeded. Human body model: 100pF discharged through a 1.5kΩ resistor between two pins of the device, done for all couples of pin combinations with other pins floating. Machine model: a 200pF cap is charged to the specified voltage, then discharged directly between two pins of the device with no external series resistor (internal resistor < 5 Ω), done for all couples of pin combinations with other pins floating. Charged device model: all pins plus package are charged together to the specified voltage and then discharged directly to the ground. The input bias currents are junction leakage currents which approximately double for every 10°C increase in the junction temperature. 2.3 NE555 Timer IC 2.3.1Overview 11 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. The IC was designed by Hans R. Camenzind in1970 and brought to market in 1971 by Signetics (later acquired by Philips). The original name was the SE555 (metal can)/NE555 (plastic DIP) and the part was described as "The IC Time Machine". It has been claimed that the 555 gets its name from the three 5 kΩ resistors used in typical early implementations, [2]

but Hans Camenzind has stated that the number was arbitrary. The part is still in

wide use, thanks to its ease of use, low price and good stability. As of 2003, it is estimated that 1 billion units are manufactured every year. Depending on the manufacturer, the standard 555 package includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8). Variants available include the 556 (a 14-pin DIP combining two 555s on one chip), and the 558 (a 16-pin DIP combining four slightly modified 555s with DIS & THR connected internally, and TR falling edge sensitive instead of level sensitive). Ultra-low power versions of the 555 are also available, such as the 7555 and TLC555. The 7555 requires slightly different wiring using fewer external components and less power. The 555 has three operating modes:

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

Monostable mode: in this mode, the 555 functions as a "one-shot".

Applications include timers, missing pulse detection, bounce free switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) etc 

Astable - free running mode: the 555 can operate as an oscillator. Uses

include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc. 

Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the

DIS pin is not connected and no capacitor is used. Uses include bounce free latched switches, etc. 2.3.2 Pin Outs & Descriptions The 555 integrated circuit is a highly accurate timing circuit that is capable of producing either time delays or oscillation.

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Fig 2.2 Pin out diagram of NE555 Timer IC V+

is the supply voltage. GND is also Ground (0V) connection for supply

voltage. Threshold is an active high input pin that is used to monitor the charging of the timing capacitor. Control Voltage is used to adjust the threshold voltage if required. This should be left disconnected if the function is not required. A 0.01uF capacitor to Gnd can be used in electrically noisy circuits. The Trigger is also an active low trigger input that starts the timer. Discharge is the output pin that is used to discharge the timing capacitor. Out is known as the Timer output pin. Reset is also an active low reset pin. Normally connected to V+ if the reset function is not required.

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Fig 2.3 NE555 Timer IC block diagram 2.3.3 Monostable Operation The circuit diagram illustrates the monostable configuration of the NE555 Timer IC.

Fig 2.4 Monostable configuration of Timer IC NE555 In monostable mode the device produces a 'one shot' pulsed output. The pulse is started by a taking the trigger input from a high (V+) to a low voltage. Once triggered the circuit remains in this state even if triggered again during the pulse interval. The pulse high time is given by: t = 1.1 x R1 x C1

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The high to low voltage transition on the trigger input causes the Flip-Flop to become set. This releases the short circuit (created by holding of the discharge pin low) across capacitor C1. At this point the output goes high. Capacitor C1 then begins to charge and the voltage across it begins to increase. When it reaches 2/3 V+ the Flip-Flop is reset. This causes capacitor C1 to discharge very quickly and the output goes low. Minimum output pulse = 5 µS Maximum output pulse = 5 minutes R1 minimum resistance = 1K ohm R1 maximum resistance = 1Mohm 2.3.4 Astable Operation The circuit diagram illustrates the astable configuration of the NE555 Timer IC.

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Fig 2.5 Astable configuration of Timer IC NE555 In astable mode the timer continually triggers itself and runs as a multi vibrator. This results in a continually repeating signal being generated on the output pin. The external capacitor C1 charges through both R1 and R2 but discharges only through R2. Therefore the duty cycle is determined by the ratio of this resistor. If the value of the two resistors is the same the duty cycle will be 50% and a square wave will be output. The 'High' output time is given by: t1 = 0.693 (R1 + R2) x C1 The 'Low' output time is given by: t2 = 0.693 (R2) x C1 Therefore the total period is given by: T = t1 + t2 = 0.693 (R1 + R2) x C1

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The frequency of oscillation is given by: f = 1 / T = 1.44 / ((R1 + R2) x C1) 2.3.5 Example Applications Joystick interface circuit using quad timer 558 The original IBM personal computer used a quad timer 558 in monostable (or "one-shot") mode to interface up to two joysticks to the host computer. In the joystick interface circuit of the IBM PC, the capacitor (C) of the RC network (see Monostable Mode above) was generally a 10nF capacitor. The resistor (R) of the RC network consisted of the potentiometer inside the joystick along with an external resistor of 2.2 kilohms. The joystick potentiometer acted as a variable resistor. By moving the joystick, the resistance of the joystick increased from a small value up to about 100 kilohms. The joystick operated at 5 V. Software running in the host computer started the process of determining the joystick position by writing to a special address (ISA bus I/O address 201h). This would result in a trigger signal to the quad timer, which would cause the capacitor (C) of the RC network to begin charging and cause the quad timer to output a pulse. The width of the pulse was determined by how long it took the C to charge up to 2/3 of 5 V (or about 3.33 V), which was in turn determined by the joystick position.

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Software running in the host computer measured the pulse width to determine the joystick position. A wide pulse represented the full-right joystick position, for example, while a narrow pulse represented the full-left joystick position. Atari Punk Console One of Forrest M. Mims III's many books was dedicated to the 555 timer. In it, he first published the "Stepped Tone Generator" circuit which has been adopted as a popular circuit, known as the Atari Punk Console, by circuit benders for its distinctive low-fi sound similar to classic Atari games. The 555 can be used to generate a variable PWM signal using a few external components. The chip alone can drive small external loads or an amplifying transistor for larger loads. CHAPTER THREE PIEZOELECTRICITY 3.1 Introduction In this chapter is a focus on piezoelectricity as the backbone behind the operation of this proposed circuit. We are going to look at the history of piezoelectricity, features of piezo element, buzzer, the proposed circuit diagram and some applications of the piezoelectricity. 3.2 History of Piezoelectricity

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3.2.1definition of Piezoelectricity Piezoelectricity is a form of electricity created when certain crystals are bent or otherwise deformed. These same crystals can also be made to bend slightly when a small current is run through them, encouraging their use in instruments for which great degrees of mechanical control are necessary. This is called converse piezoelectricity. For example, scanning tunneling microscopes (STMs) use piezoelectric crystals to “scan” the surface of a material and create images of great detail. Piezoelectricity is related to pyroelectricity, in which a current is created by heating or cooling the crystal. The property of piezoelectricity is dictated by both the atoms in the crystal and the particular way in which that crystal was formed. Some of the first substances that were used to demonstrate piezoelectricity are topaz, quartz, tourmaline, and cane sugar. Today, we know of many crystals which are piezoelectric, some of which can even be found in human bone. Certain ceramics and polymers have exhibited the effect as well. A piezoelectric crystal consists of multiple interlocking domains which have positive and negative charges. These domains are symmetrical within the crystal, causing the crystal as a whole to be electrically neutral. When stress is put on the crystal, the symmetry is slightly broken, generating voltage. Even a tiny bit of piezoelectric crystal can generate voltages in the thousands.

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Piezoelectricity is used in sensors, actuators, motors, clocks, lighters, and transducers. A quartz clock uses piezoelectricity, as does any cigarette lighter without a flint. Medical ultrasound devices create high-frequency acoustic vibrations using piezoelectric crystals. Piezoelectricity is used in some engines to create the spark which ignites the gas. Loudspeakers use piezoelectricity to convert incoming electricity to sound. Piezoelectric crystals are used in many highperformance devices to apply tiny mechanical displacements on the scale of nanometers. Even though a piezoelectric crystal never deforms by more than a few nanometers when a current is run through it, the force behind this deformation is extremely high, on the order of meganewtons. This deformational power is used in mechanics experiments and for aligning optical elements many times heavier than the piezoelectric crystal itself. 3.2.2 History The first experimental demonstration of a connection between macroscopic piezoelectric phenomena and crystallographic structure was published in 1880 by Pierre and Jacques Curie. Their experiment consisted of a conclusive measurement of surface charges appearing on specially prepared crystals (tourmaline, quartz, topaz, cane sugar and Rochelle salt among them) which were subjected to mechanical stress. These results were a credit to the Curies' imagination and

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perseverance, considering that they were obtained with nothing more than the foil, glue, wire, magnets, and a jeweler’s saw. In the scientific circles of the day, this effect was considered quite a "discovery," and was quickly dubbed as "piezoelectricity" in order to distinguish it from other areas of scientific phenomenological experience such as " electricity" (friction generated static electricity) and "pyroelectricity" (electricity generated from crystals by heating).

The Curie brothers asserted, however, that there was a one-to-one correspondence between the electrical effects of temperature change and mechanical stress in a given crystal, and that they had used this correspondence not only to pick the crystals for the experiment, but also to determine the cuts of those crystals. To them, their demonstration was a confirmation of predictions which followed naturally from their understanding of the microscopic crystallographic origins of pyroelectricity. The Curie brothers did not, however, predict that crystals exhibiting the direct piezoelectric effect (electricity from applied stress) would also exhibit the converse piezoelectric effect (stress in response to applied electric field). This property was mathematically deduced from fundamental thermodynamic principles by Lippmann in 1881. The Curies immediately confirmed the existence of the

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"converse effect," and continued on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals. 1882 – 1917 At this point in time, after only two years of interactive work within the European scientific community, the core of piezoelectric applications science was established: the identification of piezoelectric crystals on the basis of asymmetric crystal structure, the reversible exchange of electrical and mechanical energy, and the usefulness of thermodynamics in quantifying complex relationships

among

mechanical,

thermal

and

electrical

variables.

In the following 25 years (leading up to 1910), much more work was done to make this core grow into a versatile and complete framework which defined completely the 20 natural crystal classes in which piezoelectric effects occur, and defined all 18 possible macroscopic piezoelectric coefficients accompanying a rigorous thermodynamic treatment of crystal solids using appropriate tensorial analysis. In 1910 Voigt's "Lerbuch der Kristallphysik" was published, and it became the standard reference work embodying the understanding which had been reached.

During the 25 years that it took to reach Voigt's benchmark, however, the world was not holding its breath for piezoelectricity. A science of such subtlety as to require tensorial analysis just to define relevant measurable quantities paled by comparison to electro-magnetism, which at the time was maturing from a science 23 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

to a technology, producing highly visible and amazing machines. Piezoelectricity was obscure even among crystallographers; the mathematics required to understand it was complicated; and no publicly visible applications had been found for any of the piezoelectric crystals. The first serious applications work on piezoelectric devices took place during World War I. In 1917, P. Langevin and French co-workers began to perfect an ultrasonic submarine detector. Their transducer was a mosaic of thin quartz crystals glued between two steel plates (the composite having a resonant frequency of about 50 KHz), mounted in a housing suitable for submersion. Working on past the end of the war, they did achieve their goal of emitting a high frequency "chirp" underwater and measuring depth by timing the return echo. The strategic importance of their achievement was not overlooked by any industrial nation, however, and since that time the development of sonar transducers, circuits, systems, and materials has never ceased. 3.3 Applications Piezoelectric sensors have proven to be versatile tools for the measurement of various processes. They are used for quality assurance, process control and for research and development in many different industries. Although the piezoelectric effect was discovered by Curie in 1880, it was only in the 1950s that the piezoelectric effect started to be used for industrial sensing applications. Since

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then, this measuring principle has been increasingly used and can be regarded as a mature technology with an outstanding inherent reliability. It has been successfully used

in

various

applications,

such

as

in medical, aerospace,

nuclear instrumentation, and as a pressure sensor in the touch pads of mobile phones. In the automotive industry, piezoelectric elements are used to monitor combustion when developing internal combustion engines. The sensors are either directly mounted into additional holes into the cylinder head or the spark/glow plug is equipped with a built in miniature piezoelectric sensor. The rise of piezoelectric technology is directly related to a set of inherent advantages. The high modulus of elasticity of many piezoelectric materials is comparable to that of many metals and goes up to 105 N/m². Even though piezoelectric sensors are electromechanical systems that react to compression, the sensing elements show almost zero deflection. This is the reason why piezoelectric sensors are so rugged, have an extremely high natural frequency and an excellent linearity over a wide amplitude range. Additionally, piezoelectric technology is insensitive to electromagnetic fields and radiation, enabling measurements under harsh

conditions.

Some

materials

used

(especially gallium

phosphate or tourmaline) have an extreme stability even at high temperature, enabling sensors to have a working range of up to 1000°C. Tourmaline shows pyroelectricity in addition to the piezoelectric effect; this is the ability to 25 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

generate an electrical signal when the temperature of the crystal changes. This effect is also common to piezoceramic materials. One disadvantage of piezoelectric sensors is that they cannot be used for truly static measurements. A static force will result in a fixed amount of charges on the piezoelectric material. While working with conventional readout electronics, imperfect insulating materials, and reduction in internal sensor resistance will result in a constant loss of electrons, and yield a decreasing signal. Elevated temperatures cause an additional drop in internal resistance and sensitivity. The main effect on the piezoelectric effect is that with increasing pressure loads and temperature, the sensitivity is reduced due to twin-formation. While quartz sensors need to be cooled during measurements at temperatures above 300°C, special types of crystals like GaPO4 gallium phosphate do not show any twin formation up to the melting point of the material itself. However, it is not true that piezoelectric sensors can only be used for very fast processes or at ambient conditions. In fact, there are numerous applications that show quasi-static measurements, while there are other applications with temperatures higher than 500°C. Piezoelectric sensors are also seen in nature. Dry bone is piezoelectric, and is thought by some to act as a biological force sensor.

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3.4 Principle of Operation Depending on how a piezoelectric material is cut, three main modes of operation can be distinguished: transverse, longitudinal, and shear. Transverse effect A force is applied along a neutral axis (y) and the charges are generated along the (x) direction, perpendicular to the line of force. The amount of charge depends on the geometrical dimensions of the respective piezoelectric element. When dimensions a,b,c apply, Cx = dxyFyb / a,

(eqn. 3.1)

where a is the dimension in line with the neutral axis, b is in line with the charge generating axis and d is the corresponding piezoelectric coefficient. Longitudinal effect The amount of charge produced is strictly proportional to the applied force and is independent of size and shape of the piezoelectric element. Using several elements that are mechanically in series and electrically in parallel is the only way to increase the charge output. The resulting charge is Cx = dxxFxn,

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(eqn. 3.2)

where dxx is the piezoelectric coefficient for a charge in x-direction released by forces applied along x-direction (in pC/N). Fx is the applied Force in x-direction [N] and n corresponds to the number of stacked elements. Shear effect Again, the charges produced are strictly proportional to the applied forces and are independent of the element’s size and shape. For n elements mechanically in series and electrically in parallel the charge is Cx = 2dxxFxn.

(eqn. 3.3)

In contrast to the longitudinal and shear effects, the transverse effect opens the possibility to fine-tune sensitivity on the force applied and the element dimension.

3.5 Electrical Properties A piezoelectric transducer has very high DC output impedance and can be modeled as a proportional voltage source and filter network. The voltage V at the source is directly proportional to the applied force, pressure, or strain. The output signal is then related to this mechanical force as if it had ed through the equivalent circuit.

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Fig 3.1 Frequency response of a piezoelectric sensor; output voltage vs applied force A detailed model includes the effects of the sensor's mechanical construction and other non-idealities.[3] The inductance Lm is due to the seismic mass and inertia of the sensor itself. Ce is inversely proportional to the mechanical elasticity of the sensor. C0 represents the static capacitance of the transducer, resulting from an inertial mass of infinite size. Ri is the insulation leakage resistance of the transducer element. If the sensor is connected to a load resistance, this also acts in parallel with the insulation resistance, both increasing the high- cutoff frequency.

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Fig 3.2 Equivalent circuit of sensor For use as a sensor, the flat region of the frequency response plot is typically used, between the high- cutoff and the resonant peak. The load and leakage resistance need to be large enough that low frequencies of interest are not lost.

Fig 3.3 Schematic symbol and electronic model of a piezoelectric sensor A simplified equivalent circuit model can be used in this region, in which Cs represents the capacitance of the sensor surface itself, determined by the 30 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

standard formula for capacitance of parallel plates. It can also be modeled as a charge source in parallel with the source capacitance, with the charge directly proportional to the applied force, as above. 3.6 Proposed Circuit Diagram The circuit diagram below illustrates or shows the proposed circuit diagram for implementation of the seismic sensor project.

Fig 3.4 Proposed project circuit diagram

CHAPTER FOUR DESIGN & IMPLEMENTATION OF SEISMIC SENSOR 31 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

4.1 Introduction This chapter will concentrate on the general architecture and design, circuit description and operation, come design calculations, the operational flow chart and the data sheet for the design and implementation of the seismic sensor. 4.2 General Architecture of the Seismic Sensor The diagram below shows the general architecture of the proposed circuit for the project.

PIEZO PIEZO ELEMEN ELEMEN T T

AMPLIFIER AMPLIFIER CIRCUIT/UNIT CIRCUIT/UNIT

XLV1 Input

PIEZO BUZZER/SPEAKER TIMER CIRCUIT/UNIT

Fig 4.1 General architecture of seismic sensor using a piezo element 4.3 Circuit Diagram & Description

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The below diagram shows the circuitry for the seismic sensor with its description below.

Fig 4.2 Circuit diagram for the seismic sensor The circuit uses readily available components and the design is straight-forward. A standard piezo sensor is used to detect vibrations/sounds due to pressure changes. The piezo element acts as a small capacitor having a capacitance of a few nanofarads. Like a capacitor, it can store charge when a potential is applied to its terminals. It discharges through VR1, when it is disturbed. In the circuit, IC TLO71 (IC1) is wired as a differential amplifier with both its inverting and non-

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inverting inputs tied to the negative rail through a resistive network comprising R1, R2 and R3. Under idle conditions (as adjusted by VR1), both the inputs receive almost equal voltages, which keeps the output low. TLO71 is a low-noise JFET input op-amp with low input bias and offset current. The BIFET technology provides fast slew rates. Capacitor C1 is provided in the circuit to keep the differential input of IC1 for better performance. 4.4 Circuit Operation When the piezo element is disturbed (by even a slight movement), it discharges the stored charge. This alters the voltage level at the inputs of IC1 and the output momentarily swings high as indicated by green LED1. This high output is used to trigger switching transistor T1, which triggers monostable IC2. The timing period of IC2 is determined by R7 and C5. With the shown values, it will be around two minutes. The high output from IC2 activates T2 and the buzzer starts beeping along with red light indication from LED2.

4.4.1 Design Calculation 34 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

The below calculation is the basic design calculations for the transistors T1 and T2 as well as the timing period for the circuit to produce its beeping sound along with the red LED. Biasing Voltage = 1.7v (Theoretical Value) Vcc = VBE + IRRL T1; IB = 1.7/R4 = 1.7/330 = 0.0052 A, T2; IB = 1.7/R8 = 1.7/1 *103 = 0.0017 A, The timing period of IC2 is determined by R7 and C5. T = 1.11 *R5 * C7 = 1.11 * 1 x 106 * 100 x10-6 = 111 seconds. 4.5 Flow Chart 35 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

The chart below shows the flow control or processes of operation of the seismic sensor.

DISTURBANC E OF PIEZO ELEMENT

IC1 VOLTAGE LEVEL IS ALTERED

SWITCHING TRANSISTOR T2 IS TRIGGERED MONOSTABLE TO IC2 trigger

HIGH OUTPUT OF IC2 ACTIVATES T2

BUZZER STARTS TO BEEP

Fig 4.3 Flow chart for seismic sensor using piezo element 4.6 Data Sheet & Cost Analysis 36 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

Table 4.0 Component list and cost No. 1

Name Of Component Resistors

5

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 VR1 Capacitors C1 C2 C3 C4 C5 C6 Transistor T1 T2 Light Emitting Diode LED1 LED2 IC1

6 7 8 9

IC2 PZ1 PIEZO ELEMENT SWITCH

2

3 4

Specification 100kΩ 10kΩ 100kΩ 330kΩ 1kΩ 470kΩ 1MΩ 1kΩ 470kΩ 10kΩ 1MΩ 10µF,25V 0.1µF 100µF,25V 0.01µF 100µF,25V 10µF,25V npn BC548 npn BC548 Green Red TL071 low noise JFET op-amp NE555 Timer Piezo Buzzer ON/OF

Quantity 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

CHAPTER FIVE CONCLUSSION & FUTURE WORKS 37 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

Cost Gh¢

In conclusion, the disturbance made by any moving object using the piezo element seismic sensor implemented. The disturbance discharges the stored charge. This caused the IC1to produce a high output. This high output is used to trigger switching transistor IC2 and the vibration or sound or movement made is caused the buzzer to beep. The sound and vibration caused movements can also be detected by new and growing technology. This project has given any researcher or student to do any future work on the above project.

REFERENCES [1]

van Roon, "pg. 1"

38 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

[2]

Scherz, Paul (2000) "Practical Electronics for Inventors," p. 589. McGrawHill/TAB Electronics. ISBN: 978-0070580787. Retrieved 2010-04-05.

[3] Ward, Jack (2004). The 555 Timer IC - An Interview with Hans Camenzind. The Semiconductor Museum. Retrieved 2010-04-05. [4]

van Roon, Fig 3 & related text.

[5]

Jung, Walter G. (1983) "IC Timer Cookbook, Second Edition," pp. 40–41. Sams Technical Publishing; 2nd ed. ISBN: 978-0672219320. Retrieved 2010-04-05.

[6] van Roon, Chapter "Monostable Mode." [7] van Roon Chapter: "Astable operation." [8] Engdahl, pg 1. [9] Engdahl, "Circuit diagram of PC joystick interface" [10] Engdahl, "Joystick construction". [11] Engdahl, "PC analogue joystick interface". [12] Eggebrecht, p. 197. [13] Eggebrecht, pp. 197-9 [14] Piezocryst website. Retrieved 2006-06-02. [15] "Interfacing Piezo Film to Electronics" (PDF). Measurement Specialties. March 2006. Retrieved 2007-12-02. [16]

Alfredo Vázquez Carazo (January 2000). Novel Piezoelectric Transducers for High Voltage Measurements. Universitat Politècnica de Catalunya. pp. 242.

[17] Karki, James (September 2000). "Signal Conditioning Piezoelectric Sensors" (PDF). Texas Instruments. Retrieved 2007-12-02. 39 | D e s i g n & I m p l e m e n t a t i o n O f S e i s m i c S e n s o r

[18] Ludlow, Chris (May 2008). "Energy Harvesting with Piezoelectric Sensors" (PDF). Mide Technology. Retrieved 2008-05-21. [19]

B. L kakrati and A. K fsator, “PLC,” 24th Edition, Scand and Company, New Delhi, 2000.

[20]

J. B Gupta, “Electrical Technology,” 12th Edition, S. K Kataria and Sons, Delhi, 2003.

[21] D. G. Fink and H. W. Beaty, “Standard Handbook for Electrical Engineers,” 13thEdition, McGraw Hill, Singapore, 1993. [22] J. O. Bird and P. J Chivers, “Engineering and Physical Science Pocket Book,” Newnew 1995. [23] H. Uppal , “ Electrical Power System,” 3rd Edition, New Delhi, India, 1995.

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