VARDHAMAN COLLEGE OF ENGINEERING (Approved by AICTE, New Delhi, Affiliated to JNTUH and Accredited by NBA)
MINI PROJECT ON KNOCK ALARM USING PIEZOELECTRIC MATERIAL
UNDER THE GUIDENCE OF MRS. A. VIJAYA LAKSHMI BY B.RAJA SHEKAR (08881A0430)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
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Abstract In this modern world everyone wants something new, something different, so instead of using a switch to ring the door bell just an alarm is produced by knocking the door which people feel more luxurious. The circuit of automatic alarm on knocking uses a thin piezoelectric plate, senses the vibration generated on knocking a surface (such as a door or a table) to activate the alarm and can also be used to safeguard motor vehicles. The piezoelectric plate is used as the sensor. It consist IC 555 Timer to which speaker is connected at the output. Piezoelectric material is used at the input in order to convert any mechanical vibration into electrical variation, it avoids false triggering. The plate can be fixed on a door, cash box, cupboard, etc using adhesive. A 1-1.5m long, shielded wire is connected between the sensor plate and the input of the circuit. A led is placed at the output of the IC 555 Timer. The circuit operates off a 9V or a 12V battery.
Contents:
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1) Intr Introd oduc ucti tion on 2) Bloc Block k Diag Diagra ram m 3) Resistors and Capacitors
4) Tran Transsisto istorrs 5) Diode 6) Inte Integr grat ated ed Circ Circui uitt i.
555 Timer a) Input nputss of 555 555 b) Output of 555
c) Loud oud Speak peaker er d) Relay Relay coils coils and and other other induct inductive ive load loadss e) 555 555 Asta Astabl blee mod modee f) Asta Astabl blee Ope Opera rati tion on g) Duty Cy Cycle 1) Piez Piezoe oele lect ctri ricc Sens Sensor or i.
Introducti ction
ii. ii. Compar Compariso ison n of sensin sensing g princi principle pless iii. Principle Principle Of Operation Operation a) Tran Transv sver erse se eff effec ectt b) b) Long Longit itud udin inal al eff effec ectt c) Shear hear effe effect ct i.
Sensor Des Design
ii. ii. Piezoel Piezoelect ectric ric energ energy y harvest harvesting ing iii. iii. Mate Materi rial alss iv. Specif Specifica icatio tions ns a) Stan Standa dard rd pro produ duct ctss b) b) Cons Constr truc ucti tion on c) Elec Electr tric ic perf perfor orma mance nce d) Mech Mechan anic ical al perfo perform rman ance ce e) Enviro Environme nmenta ntall perfor performan mance ce i. Oper Operat atin ing g Prec Precau auta tati tion onss
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a) Appl Appliicat cations ions b) Precau Precautio tion n for handli handling ng i.
Prec Precau auti tion onss for for safe safety ty
ii. Prohib Prohibit ited ed applica applicatio tions ns iii. iii. Applic Applicati ation on notes notes 1) Circui Circuitt diagr diagram am and Workin Working g 2) Conc Concllusi usion i.
Results
ii. Adva Advant ntag ages es iii. iii. Applica Applicati tions ons
Chapter 1 Introduction
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The circuit of Knock alarm uses a thin piezoelectric plate, senses the vibration generated on knocking a surface (such as a door or a table) to activate the alarm and can also be used to safeguard motor vehicles. The piezoelectric plate is used as the sensor. It consist IC 555 Timer to which speaker is connected at the output. Piezoelectric material is used at the input in order to conver convertt any mechani mechanical cal vibrat vibration ion into into electr electrica icall variat variation ion,, it avoids avoids false false trigger triggering ing.. When When someone knocks on the door, the piezoelectric sensor generates an electrical signal, which is amplified by transistors. The amplified signal is rectified and filtered to produce a low-level DC voltage, which is further amplified by the remaining transistors. The final output from the collector of PNP transistor is applied to reset pin 4 of 555 Timer that is wired as an astable multi vibrator. Whenever the collector of transistor T6 goes high, the astable multi vibrator activates to sound an alarm through the speaker. speaker. When the circuit receives receives an input signal due to knocking, knocking, the alarm alarm gets gets activa activated ted for about about 7 seconds seconds.. The plate plate can be fixed fixed on a door, door, cash cash box, box, cupboard, etc using adhesive. A 1-1.5m long, shielded wire is connected between the sensor plate and the input of the circuit. A led is placed at the output of the IC 555 Timer. The circuit operates off a 9V or a 12V battery.
Chapter 2
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Piezoelectric Sensor: A piezoel piezoelect ectric ric sensor sensor is a materi material al which which conver converts ts mechani mechanical cal variat variation ionss and electr electrica icall variations.
Amplifier: Amplifier Amplifier is a device which increases increases the strength strength of the signal. signal. when a signal with low strength is given as the input to the amplifier then the amplifier increases the strength of that signal.
Rectifier: Rectifier is a device which converts A.C. voltage (Bi-directional) into pulsating D.C. (Unidirectional).
Filter: Filter Filter is a device which which minimize the ripple content content (or) fluctuati fluctuations ons in the signal. Ideally, the output of the filter should be pure d.c. practically, the filter circuit will try to minimize the ripple at the output.
555 Timer: The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. It is a monolithic timing circuit that can produce accurate and highly stable time delays or oscillations.
Speaker and LED: Speaker produces sound. Light Emitting Diode which produces light.
Chapter 3
Resistors and Capacitors Resistors: Introduction
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A resi resist stor or is a twotwo-terminal terminal electronic electronic component component that produces a voltage across its terminals that is proportional is proportional to the electric current through it in accordance with Ohm's law: law: V = V = IR Resistors are elements of electrical of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome).
Fig : resistor code
The primary characteristics of a resistor are the resistance, resistance, the tolerance, tolerance, the maximum working voltage and the power the power rating. rating. Other characteristics include temperature coefficient, noise, noise, and inductance. inductance. Less well-known is critical resistance, resistance, the value below which power dissipation limits the maximum permitted current, and above which the limit is applied voltage. Critical resistance is determined by the design, materials and dimensions of the resistor. Resistors can be integrated into hybrid and printed p rinted circuits, as well as integrated circuits. Size, and position of leads (or terminals), are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power.
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Fig. Resistor color code Theory of operation Ohm's law
The behavior of an ideal resistor is dictated by the relationship specified in Ohm's law: Ohm's law states that the voltage (V) across a resistor is proportional to the current (I) through it where the constant of proportionality is the resistance (R). Equivalently, Ohm's law can be stated:
This formulation of Ohm's law states that, when a voltage (V) is maintained across a resistance (R), a current (I) will flow through the resistance. This formulation is often used in practice. For example, if V is 12 volts and R is 400 4 00 ohms, a current of 12 / 400 = 0.03 amperes will flow through the resistance R. Resistors used in Knock Alarm using piezoelectric material Circuitry:
100 ii. 470 i.
Ω
iii. 1 K iv. 3.3 v. 10
Ω Ω KΩ KΩ
8
vi. 22
KΩ
vii. 47
KΩ
viii. 82
KΩ
ix. 220
KΩ
x. 330
KΩ
xi. 1
MΩ
Capacitors: A capacitor is an electrical device that can store energy in the electric field between a pair of closely spaced conductors (called 'plates'). When current is applied to the capacitor, electric charges of equal magnitude, but opposite polarity, build up on each plate. Capacitors are used in electrical circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals and this makes them useful in electronic filters. Capaci Capacitor torss are occasi occasional onally ly referr referred ed to as condens condensers ers.. This This is now conside considered red an antiquated term. The capacitor's capacitance (C) is a measure of the amount of charge (Q) stored on each plate for a given potential difference or voltage (V) which appears between the plates:
C=Q/V
In SI units, a capacitor has a capacitance of one farad when one coulomb of charge is stored due to one volt applied potential difference across the plates. Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (µF), nanofarads (nF), or picofarad (pF). The capacitance is proportional to the surface area of the conducting plate and inversely proportional to the distance between the plates. It is also proportional to the permittivity of the dielectric (that is, non-conducting) substance that separates the plates.
Capacitor types:
Vacuum:
Two metal, metal, usuall usually y copper, copper, electr electrodes odes are separa separated ted by a vacuum vacuum.. The insula insulatin ting g envelope is usually glass or ceramic. Typically of low capacitance - 10 - 1000 pF and high
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voltage, up to tens of kilovolts, they are most often used in radio transmitters and other high voltage power devices. Both fixed and variable types are available. Variable vacuum capacitors can have a minimum to maximum capacitance ratio of up to 100, allowing any tuned circuit to cover a full decade of frequency. Vacuum is the most perfect of dielectrics with a zero loss tangent. This allows very high powers to be transmitted without significant loss and consequent heating.
Air:
Air dielectric capacitors consist of metal plates separated by an air gap. The metal plates, of which there may be many interleaved, are most often made of aluminum or silver-plated brass. Nearly all air dielectric capacitors are variable and are used in radio tuning circuits.
Metalized plastic film:
Made Made
from from
high high
qual qualit ity y
poly polyme merr
film film
(usu (usual ally ly
poly polyca carb rbon onat ate, e,
poly polyst styr yren ene, e,
polypropylene, polyester (Mylar), and for high quality capacitors polysulfone), and metal foil or a layer of metal deposited on surface. They have good quality and stability, and are suitable for timer circuits suitable for high frequencies.
Mica:
Simila Similarr to metal metal film, film, often often high high voltag voltage, e, suitab suitable le for high high frequen frequencie cies, s, expens expensive ive,, excellent tolerance.
Paper:
Used for relatively high voltages. Now obsolete.
Glass:
Used Used for high high voltag voltages, es, expens expensive ive,, stable stable temper temperatu ature re coeffic coefficien ientt in a wide wide range range of temperatures.
Ceramic:
Chips of alternating layers of metal and ceramic. Depending on their dielectric, whether Class 1 or Class 2, their degree of temperature/capacity dependence varies. They often have
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(especially the class 2) high dissipation factor, high frequency coefficient of dissipation, their capacity capacity depends on applied applied voltage, and their capacity capacity changes with aging. However they find massive use in common low-precision coupling and filtering applications, suitable for high frequencies.
Aluminum electrolytic:
Polarized, Polarized, constructional constructionally ly similar to metal film, but the electrodes electrodes are made of etched aluminum to acquire much larger surfaces. The dielectric is soaked with liquid electrolyte. They can achieve high capacities but suffer from poor tolerances, high instability, gradual loss of capacity especially when subjected to heat, and high leakage. Tend to lose capacity in low temperatures. Bad frequency characteristics make them unsuited for high-frequency applications. Special types with low equivalent series resistance are available.
Tantalum electrolytic:
Similar to the aluminum electrolytic capacitor but with better frequency and temperature characteristics, high dielectric absorption, high leakage. Has much better performance in low temperatures.
Super capacitors:
Made Made from from carbon carbon aeroge aerogel, l, carbon carbon nanotu nanotubes bes,, or highly highly porous porous electr electrode ode materia materials. ls. Extremely high capacity and can be used in some applications instead of rechargeable batteries.
Gimmick capacitors:
These are capacitors made from two insulated wires that have been twisted together. Each wire forms a capacitor plate. Gimmick capacitors are also a form of variable capacitor. Small changes in capacitance (20 percent or less) are obtained by twisting and untwisting the two wires.
Varicap capacitors:
These are specialized, reverse-biased diodes whose capacitance varies with voltage. Used in phase-locked loops, amongst other applications.
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Capacitors used in this project are: •
0. 0 1
µF
•
0. 1
µF
•
22
µF
•
47
µF
•
100
µF
Chapter 4 Transistor A transistor is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
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The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolu revolutio tionis nised ed the field field of electr electroni onics, cs, and paved paved the way for smalle smallerr and cheape cheaperr radios radios,, calculators, and computers, amongst other things. A bipolar bipolar junction junction transistor transistor (BJT) is a three-term three-terminal inal electronic electronic device constructed constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar applications. Bipolar transistors are so named because their operation involves both electrons and holes. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of diff differ erent ent char charge ge conce concent ntra rati tion ons. s. This This mode mode of oper operat atio ion n is contr contras aste ted d with with unipolar transistors, such as field-effect transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices. minority-carrier devices.
Introduction
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Fig:-1 NPN BJT with forward-biased E–B junction and reverse-biased B–C junction An NPN transistor can be considered as two diodes with a shared anode. In typical operation, the base-emitter junction is forward biased and the base–collector junction is reverse biased. In an NPN transistor, for example, when a positive voltage is applied to the base–emitter junction, the equilibrium between thermally generated carriers and the repelling electric field of the depletion region becomes region becomes unbalanced, allowing thermally excited electrons to inject into the base region. These electrons wander (or "diffuse") through the base from the region of high concentration near the emitter towards the region of low concentration near the collector. The electrons in the base are called minority carriers because the base is doped p-type which would carrier in the base. make holes the majority carrier in To minimize the percentage of carriers that recombine before reaching the collector–base junction, the transistor's base region must be thin enough that carriers can diffuse across it in much less time than the semiconductor's minority carrier lifetime. In particular, the thickness of the base must be much less than the diffusion length of the electrons. The collector–base junction is reverse-biased, and so little electron injection occurs from the collector to the base, but electrons that diffuse through the base towards the collector are swept into the collector by the electric field in the depletion region of the collector–base junction. The thin shared base and asymmetric collector–emitter doping is what differentiates a bipolar transistor from two separate two separate and oppositely biased diodes connected in series.
4.2 Voltage, current, and charge control The collector–emitter current can be viewed as being controlled by the base–emitter current (current control), or by the base–emitter voltage (voltage control). These views are 14
relate related d by the curren current–v t–volt oltage age relati relation on of the base–em base–emitt itter er juncti junction, on, which which is just just the usual usual exponential current–voltage curve of a p-n a p-n junction (diode)
Fig. 2 Voltage, current, and charge control
The physical explanation for collector current is the amount of minority-carrier charge in the base region. region.[1][2][3] Detailed models of transistor action, such as the Gummel–Poon model, model, account for the distribution of this charge explicitly to explain transistor behavior more exactly.[4] The charge-control view easily handles phototransistors, phototransistors, where minority carriers in the base region region are create created d by the absorp absorpti tion on of photons of photons,, and handles the dynamics of turn-off, or recovery time, which depends on charge in the base region recombining. However, because base charge is not a signal that is visible at the terminals, the current- and voltage-control views are generally used in circuit design and analysis. ana lysis. In analog circuit circuit design design,, the curren current-c t-cont ontrol rol view view is someti sometimes mes used used becaus becausee it is approximate approximately ly linear. linear. That is, the collector collector current is approximate approximately ly β F times the base current. Some basic circuits can be designed by assuming that the emitter–base voltage is approximately constant, and that collector current is beta times the base current. However, to accurately and reliably design production BJT circuits, the voltage-control (for example, Ebers–Moll) Ebers–Moll) model is required[1] required[1].. The voltage-control model requires an exponential function to be taken into account, but when it is linearized such that the transistor can be modelled as a transconductance, as in the Ebers–Moll model, model, design for circuits such as differential amplifiers again becomes a mostly linear problem, so the voltage-control view is often preferred. For translinear circuits, circuits, in which 15
the exponential I–V curve is key to the operation, the transistors are usually modelled as voltage controlled with transconductance proportional to collector current. In general, transistor level circuit circuit design is performed performed using SPICE or a comparable analogue circuit simulator, so model complexity is usually not of much concern to the designer.
Turn-on, turn-off, and storage delay The Bipola Bipolarr transi transisto storr exhibi exhibits ts a few delay charac character terist istics ics when when turnin turning g on and off. off. Most Most transistors, and especially power transistors, exhibit long base storage time that limits maximum frequency of operation in switching applications. One method for reducing this storage time is by using a Baker clamp.
Transistor 'alpha' and 'beta' The proportion of electrons able to cross the base and reach the collector is a measure of the BJT efficiency. The heavy doping of the emitter region and light doping of the base region cause many more electrons to be injected from the emitter into the base than holes to be injected from the base into the emitter. The common-emitter current gain is repres represent ented ed by βF or hfe; it is approximately the ratio of the DC collector current to the DC base current in forward-active region. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications. Another important parameter is the common-base current gain gain,, αF. The common-base current gain is approximately the gain of current from emitter to collector in the forward-active region. This ratio usually has a value close to unity; between 0.98 and and 0.998 0.998.. Alph Alphaa and and beta beta are are more more prec precis isel ely y rela relate ted d by the the foll follow owin ing g iden identi titi ties es (NPN (NPN transistor):
Structure
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Fig Simplified cross section section of a planar NPN bipolar junction transistor
A BJT consists of three differently doped semiconductor regions, the emitter region, the base region and the collector region. These regions are, respectively, p type, n type and p type in a PNP, and and n type type,, p type type and n type type in a NPN transistor . Each semiconductor region is connected to a terminal, appropriately labeled: e mitter (E), base (B) and collector (C). The base is physically located between the emitter and the collector and is made from lightly doped, high resistivity material. The collector surrounds the emitter region, making it almost impossible for the electrons injected into the base region to escape being collected, thus making the resulting value of α very close to unity, and so, giving the transistor a large β. A cross section view of a BJT indicates that the collector–base junction has a much larger area than the emitter–base junction.
NPN
Fig The symbol of an NPN Bipolar Junction Transistor.
NPN is one of the two types of bipolar transistors, in which the letters "N" (negative) and "P" (positive) refer to the majority charge carriers inside the different regions of the transistor. Most bipolar transistors used today are NPN, because electron mobility is higher than hole mobility in semiconductors, allowing greater currents and faster operation.
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NPN transistors consist of a layer of P-doped P- doped semiconductor (the "base") between two N-doped layers. A small current entering the base in common-emitter mode is amplified in the collector output. output. In other terms, an NPN transistor transistor is "on" when its base is pulled high relative relative to the emitter. The arrow in the NPN transistor symbol is on the emitter leg and points in the direction of the conventional current flow when the device is in forward active mode. Transistors used in this project are: •
BC 548 (NPN)
•
BC 549 (NPN)
•
BC 557 (PNP)
Chapter 5 Diode Introduction:
In electronics, electronics, a diod diodee is a twotwo-terminal terminal electronic electronic component component that conducts electric current in only only one direct direction ion.. The term term usuall usually y refers refers to a semico semiconduc nductor tor diode, the most most common type today. This is a crystalline piece of semiconductor material connected to two electrical electrical terminals terminals..[1] A vacuu vacuum m tube tube diod diodee (now (now litt little le used used exce except pt in some some high high-p -pow ower er technologies) is a vacuum tube with two electrodes: electrodes: a plate a plate and a cathode. cathode.
Fig: Diode The most common function of a diode is to allow an electric current to pass in one direct direction ion (calle (called d the diode' diode'ss forwar forward d bias bias direct direction ion)) while while blocki blocking ng curren currentt in the opposi opposite te direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a 18
check valve. valve. This unidirectional behavior is called rectification, rectification, and is used to convert con vert alternating current to direct current, and to extract modulation from radio signals in radio receivers. However, diodes can have more complicated behavior than this simple on-off action.This is due to their complex non-linear electrical characteristics, which can be tailored by varying the construction of their P-N junction. These are exploited in special purpose diodes that perform many different functions. For example, specialized diodes are used to regulate voltage (Zener diodes diodes), ), to electr electroni onical cally ly tune tune radio radio and TV receiv receivers ers (varac (varactor tor diodes diodes), ), to generat generatee radio radio frequency oscillations (tunnel diodes), and to produce light (light (light emitting diodes). diodes). Tunnel diodes exhibit negative resistance, which makes them useful in some types of circuits. Diode used in the present project is 1N4148 Features: •
Hermetically sealed leaded glass SOD27 (DO-35) package
•
High switching speed: max. 4 ns
•
General application
•
Continuous reverse voltage: max. 100 V
•
Repetitive peak reverse voltage: max. 100 V
•
Repetitive peak forward current: max. 450 mA.
Applications: •
High-speed switching.
Description:
The 1N4148 1N4148 is high-s high-spee peed d switch switching ing diodes diodes fabric fabricate ated d in planar planar technol technology ogy,, and encapsulated in hermetically sealed leaded glass SOD27 (DO-35) packages.
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Chapter 6 Integrated circuit circuit Introduction
In elec electr tron onic ics, s, an inte integr grat ated ed circ circui uitt (als (also o know known n as IC, IC, chip chip,, or micr microc ochi hip) p) is a miniaturi miniaturized zed electronic electronic circuit (consisti (consisting ng mainly mainly of semiconduct semiconductor or devices, devices, as well as passive passive components) that has been manufactured in the surface of a thin substrate of semiconductor material. Integrated circuits are used in almost all electronic equipment in use today and have revolutionized the world of electronics. Computers, cellular phones, and other digital appliances are now inextricable parts of the structure of modern societies, made possible by the low cost of production of integrated circuits. A hybrid hybrid integrated integrated circuit is a miniaturi miniaturized zed electronic electronic circuit constructe constructed d of individual individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board. A monolithic integrated circuit is made of devices manufactured by diffusion of trace elements into a single piece of semiconductor substrate, a chip.
Fig. Integrated Circuit Integrated circuits were made possible by experimental discoveries which showed that semiconductor devices could perform the functions of vacuum tubes and by mid-20th-century technology advancements in semiconductor device fabrication. The integration of large numbers of tiny transistors into a small chip was an enormous improvement over the manual assembly of circui circuits ts using using electr electroni onicc compone components nts.. The integr integrate ated d circui circuits ts mass mass product production ion capabi capabilit lity, y, reli reliab abil ilit ity, y, and and build buildin ing-b g-blo lock ck appr approa oach ch to circ circui uitt desi design gn ensu ensure red d the the rapi rapid d adopt adoptio ion n of standardized ICs in place of designs using discrete transistors.
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There are two main advantages of ICs over discrete circuits: cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography and not constructed as one transistor at a time. Furthermore, much less material is used to construct a circuit as a packaged IC die than as a discrete circuit. Performance is high since the components switch quickly and consume little power (compared to their discrete counterparts) because the components are small and close together. As of 2006, chip areas range from a few square millimeters to around 350 mm2, with up to 1 million transistors per mm2.
555 timer circuits Introduction
The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. It is a monolithic timing circuit that can produce accurate and highly stable time delays or oscillations. With just a few external components it can be used to build many circuits, not all of them involve timing! It was produced by Signetics Corporation in early 1970. The original name was the SE555/NE555 and was called "The IC Time Machine". The 555 gets its name from the three 5-KΩ resistors used in typical early implementations. It is widely used because of its ease to use, low price and reliability. It is one of the most popular and versatile integrated circuits which can be used to build lots of different circuits. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8) A popular version is the NE555 and this is suitable in most cases where a '555 timer' is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams on this page show a 555, but they could all be adapted to use one half of a 556.
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Fig.555 and 556 pin configurations Low power versions of the 555 are made, such as the ICM7555, but these should only be used when specified (to increase battery life) because their maximum output current of about 20mA (with a 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555. The circuit symbol for a 555 is a box with the pins arranged to suit the circuit diagram: for example example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually Usually just the pin numbers are used and they are not labeled with their function. The 555 Timer can be used with a supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum). Standard 555 ICs create a significant 'glitch' on the supply when their output changes state. This is rarely a problem in simple circuits with no other ICs, but in more complex circuits a smoothing capacitor (eg: 100µF) should be connected across the +Vs and 0V supply near the 555. A 555 Timer can be operated under following modes: •
Astable - Producing a square wave
•
Monostable - Producing a single pulse when triggered
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•
Bistable - A simple memory which can be set and reset
•
Buffer - An inverting buffer bu ffer (Schmitt trigger)
The The time timerr basi basical cally ly oper operat ates es in one one of the the two two mode modes— s—mo mono nost stab able le (one (one-s -shot hot)) multiv multivibr ibrato atorr or as an astabl astablee (free(free-run runnin ning) g) multi multivib vibrat rator. or. In the monost monostabl ablee mode, mode, it can produce accurate time delays from microseconds to hours. In the astable mode, it can produce rectangular waves with a variable duty cycle. Frequently, the 555 is used in astable mode to generate a continuous series of pulses, but you can also use the 555 to make a one-shot or monostable circuit.
Fig. Pin diagram of 555
Definition
of
Timer
Pin
Functions:
Pin 1 (Ground):
The ground (or common) pin is the most-negative supply potential of the device, which is normally connected to circuit common (ground) when operated from positive supply voltages.
Pin 2 (Trigger):
This pin is the input to the lower comparator and is used to set the latch, which in turn causes the output to go high. This is the beginning of the timing sequence in monostable operation. Triggering is accomplished by taking the pin from above to below a voltage level of 1/3 V+ (or, in general, one-half the voltage appearing at pin 5). The action of the trigger input is level-sensitive, allowing slow rate-of-change waveforms, as well as pulses, to be used as trigger sources. The trigger pulse must be of shorter duration than the time interval determined by the external R and C. If this pin is held low longer than that, the output will remain high until the 23
trigger input is driven high again. One precaution that should be observed with the trigger input signal is that it must not remain lower than 1/3 V+ for a period of time longer than the timing cycle. If this is allowed to happen, the timer will re-trigger itself upon termination of the first output pulse. Thus, when the timer is driven in the monostable mode with input pulses longer than than the desir desired ed output output pulse pulse width, width, the input input trigger trigger should effective effectively ly be short shortened ened by differentiation. The minimum allowable pulse width for triggering is somewhat dependent upon pulse level, but in general if it is greater than the 1uS (micro-Second), triggering will be reliable. A second second precau precautio tion n with with respec respectt to the trigger trigger input input concer concerns ns storag storagee time time in the lower comparator.This portion of the circuit can exhibit normal turn-off delays of several microseconds after triggerin triggering; g; that is, the latch can still still have a trigger input for this period of time after the trigger pulse. In practice, this means the minimum monostable output pulse width should be in the order of 10uS to prevent possible double triggering due to this effect. The voltage range that can safely be applied to the trigger pin is between V+ and ground. A dc current, termed the trigge triggerr curren current, t, must must also also flow flow from from this this termin terminal al into into the extern external al circui circuit. t. This This curren currentt is typically 500nA (nano-amp) and will define the upper limit of resistance resistance allowable from pin 2 to ground. For an astable configuration operating at V+ = 5 volts, this resistance is 3 Mega-ohm; it can be greater for higher V+ levels.
Pin 3 (Output):
The output of the 555 comes from a high-current totem-pole stage made up of transistors Q20 - Q24. Transistors Transistors Q21 and Q22 provide provide drive for source-type source-type loads, loads, and their Darlington Darlington connection provides a high-state output voltage about 1.7 volts less than the V+ supply level used. Transistor Q24 provides current-sinking capability for low-state loads referred to V+ (such as typical TTL inputs). Transistor Q24 has a low saturation voltage, which allows it to interface directly, with good noise margin, when driving current-sinking logic. Exact output saturation levels vary markedly with supply voltage, however, for both high and low states. At a V+ of 5 volts, volts, for instance, instance, the low state state Vce(sat) Vce(sat) is typically typically 0.25 volts at 5 mA. Operating Operating at 15 volts, volts, however, it can sink 200mA if an output-low voltage level of 2 volts is allowable (power dissipation should be considered in such a case, of course). High-state level is typically 3.3 volts at V+ = 5 volts; 13.3 volts at V+ = 15 volts. Both the rise and fall times of the output waveform are quite fast, typical switching times being 100nS. 1 00nS. The state of the output pin will always reflect
24
the inverse of the logic state of the latch, and this fact may be seen by examining. Since the latch itself is not directly accessible, this relationship may be best explained in terms of latch-input trigger conditions. To trigger the output to a high condition, the trigger input is momentarily taken from a higher to a lower level. level. [see "Pin 2 - Trigger"]. Trigger"]. This causes the latch to be set and the output to go high. Actuation of the lower comparator is the only manner in which the output can be placed in the high state. The output can be returned to a low state by causing the threshold to go from a lower to a higher level [see "Pin 6 - Threshold"], which resets the latch. The output can also be made to go low by taking the reset to a low state near ground [see "Pin 4 Reset"]. The output voltage available at this pin is approximately equal to the Vcc applied to pin 8 minus 1.7V.
Pin 4 (Reset):
This pin is also used to reset the latch and return the output to a low state. The reset voltage threshold level is 0.7 volt, and a sink current of 0.1mA from this pin is required to reset the device. These levels are relatively independent of operating V+ level; thus the reset input is TTL compatible for any supply voltage. The reset input is an overriding function; that is, it will force the output to a low state regardless of the state of either of the other inputs. It may thus be used to terminate an output pulse prematurely, to gate oscillations from "on" to "off", etc. Delay time from reset to output is typically on the order of 0.5 μS, and the minimum reset pulse width is 0.5 μS. Neither of these figures is guaranteed, however, and may vary from one manufacturer to another. In short, the reset pin is used to reset the flip-flop that controls the state of output pin 3. The pin is activated when a voltage level anywhere between 0 and 0.4 volt is applied to the pin. The reset pin will force the output to go low no matter what state the other inputs to the flipflop are in. When not used, it is recommended that the reset input be tied to V+ to avoid any possibility of false resetting.
Pin 5 (Control Voltage):
This pin allows direct access to the 2/3 V+ voltage-divider point, the reference level for the upper comparator. It also allows indirect access to the lower comparator, as there is a 2:1 divider (R8 - R9) from this point to the lower-comparator reference input, Q13. Use of this
25
terminal is the option of the user, but it does allow extreme flexibility by permitting modification of the timing period, resetting of the comparator, etc. When the 555 timer is used in a voltagecontrolled mode, its voltage-controlled operation ranges from about 1 volt less than V+ down to within 2 volts of ground (although this is not guaranteed). Voltages can be safely applied outside these limits, but they should be confined within the limits of V+ and ground for reliability. By applying a voltage to this pin, it is possible to vary the timing of the device independently of the RC network. The control voltage may be varied from 45 to 90% of the Vcc in the monostable mode, making it possible to control the width of the output pulse independently of RC. When it is used in the astable mode, the control voltage can be varied from 1.7V to the full Vcc. Varying the voltage in the astable mode will produce a frequency modulated (FM) output. In the event the control-voltage pin is not used, it is recommended that it be bypassed, to ground, with a capacitor of about 0.01uF (10nF) for immunity to noise, since it is a comparator input. This fact is not obvious in many 555 circuits since I have seen many circuits with 'no-pin-5' connected to anything, but this is the proper procedure. The small ceramic cap may eliminate false triggering.
Pin 6 (Threshold):
Pin 6 is one input to the upper comparator (the other being pin 5) and is used to reset the latch, which causes the output to go low. Resetting via this terminal is accomplished by taking the terminal from below to above a voltage level of 2/3 V+ (the normal voltage on pin 5). The action of the threshold pin is level sensitive, allowing slow rate-of-change waveforms. The voltage range that can safely be applied to the threshold pin is between V+ and ground. A dc current, termed the threshold current, must also flow into this terminal from the external circuit. This current is typically 0.1μA, and will define the upper limit of total resistance allowable from pin 6 to V+. For either timing configuration operating at V+ = 5 volts, this resistance is 16 Megaohm. For 15 volt operation, the maximum value of resistance is 20 MegaOhms.
Pin 7 (Discharge):
This pin is connected to the open collector of a npn transistor (Q14), the emitter of which goes to ground, so that when the transistor is turned "on", pin 7 is effectively shorted to ground. Usually the timing capacitor is connected between pin 7 and ground and is discharged when the
26
transistor turns "on". The conduction state of this transistor is identical in timing to that of the output stage. It is "on" (low resistance to ground) when the output is low and "off" (high resistance to ground) when the output is high. In both the monostable and astable time modes, this transistor switch is used to clamp the appropriate nodes of the timing network to ground. Saturation voltage is typically below 100mV (milli-Volt) for currents of 5 mA or less, and offstate leakage is about 20nA (these parameters are not specified by all manufacturers, however). Maximum collector current is internally limited by design, thereby removing restrictions on capacitor size due to peak pulse-current discharge. In certain applications, this open collector output can be used as an auxiliary output terminal, with current-sinking capability similar to the output (pin 3).
Pin 8 (V+):
The V+ pin (also referred to as V cc) is the positive supply voltage terminal of the 555 timer IC. Supply-voltage operating range for the 555 is +4.5 volts (minimum) to +16 volts (maximum), and it is specified for operation between +5 volts and +15 volts. The device will operat operatee essent essential ially ly the same same over over this this range range of voltag voltages es withou withoutt change change in timin timing g period period.. Actual Actually ly,, the most most signif significa icant nt operati operational onal differ difference ence is the output output drive drive capabi capabili lity, ty, which which increases for both current and voltage range as the supply voltage is increased. Sensitivity of time interval to supply voltage change is low, typically 0.1% per volt. There are special and military devices available that operate at voltages as high as 18 volts.
In the present project IC 555 Timer is operated under Astable multivibrator mode.
ASTABLE MULTIVIBRATOR:
An astabl astablee circui circuitt produce producess a 'squar 'squaree wave' wave' , this this is a digit digital al wavefo waveform rm with with sharp sharp transitions between low (0V) and high (+Vs). Note that the durations of the low and high states may be different. The circuit is called an astable because it is not stable in any state: the output is continually changing between 'low' and 'high'.
27
Fig.: 555 Timer circuit
Fig.: 555 Astable output,
a square wave(Tm and
Ts may be different) The tim timee pe perio riod d (T) of the square wave is the time for one complete cycle, but it is usually better to consider frequency consider frequency (f) which is the number of cycles per second. T = 0.7 × (R 1 + 2R 2) × C1 and f =
1.4 (R 1 + 2R 2) × C1
Where, T = Time period in seconds (s) f = Frequency in hertz (Hz) R 1 = Res Resis ista tanc ncee in in ohms ohms ( ) R 2 = Res Resis ista tanc ncee in in ohms ohms ( ) C1 = Capacitance in farads (F) The time period can be split into two parts: T = Tm + Ts Mark time (output high): Tm = 0.7 × (R 1+R 2) × C1
28
Space time (output low): Ts = 0.7 × R 2 × C1
Many circuits require Tm and Ts to be almost equal; this is achieved if R 2 is much larger than R 1. For a standard astable circuit Tm cannot be less than Ts, but this is not too restricting because the output can both sink and source current. For example an LED can be made to flash briefly with long gaps by connecting it (with its resistor) between +Vs and the output. This way the LED is on during Ts, so brief flashes are achieved with R1 larger than R2, making Ts short and Tm long. If Tm is less than Ts a diode can be added to the circuit as explained under du under duty ty cycle cyc le below. below.
Choosing R 1, R 2 and C1:
R 1 and R 2 should should be be in the the range range 1k 1k
to 1M . It is is best best to choo choose se C1 first first becau because se capaci capacitor torss are are
available in just a few values. •
Choose C1 to suit the frequency range you require (use the table as a guide).
•
Choose R 2 to give the frequency (f) you requires. Assume that R1 is much smaller than
R 2 (so that Tm and Ts are almost equal), then you can use: R 2 = 0.7/f×C1 •
about a tenth tenth of R2 R2 (1k Choose R1 to be about
min.) unless you want want the mark mark time time Tm to to be
significantly longer than the space time Ts. •
If you wish to use a variable resistor it is best to make it R2.
•
If R1 is is variable variable it must have have a fixed fixed resistor resistor of at least least 1k (this is not required for R2 if it is variable).
29
in series series
555 astable frequencies C1
R2 = 10k R2 = 100k R2 = 1M R1 = 1k R1 = 10k R1 = 100k
0.001µF 68kHz
6.8kHz
680Hz
0.01µF
6.8kHz
680Hz
68Hz
0.1µF
680Hz
68Hz
6.8Hz
1µF
68Hz
6.8Hz
0.68Hz
10µF
6.8Hz
0.68Hz 0.068Hz (41 per min.) (4 per min.)
Fig. Table of different frequencies of 555 Timer
Astable operation:
With the output high (+Vs) the capacitor C1 is charged by current flowing through R1 and R2. The threshold and trigger inputs monitor the capacitor voltage and when it reaches 2/3Vs (threshold voltage) the output becomes low and the discharge pin is connected to 0V.
Fig. Astable 555 Timer input and output waveforms The capacitor now discharges with current flowing through R2 into the discharge pin. When the voltage falls to 1/3Vs (trigger voltage) the output becomes high again and the discharge pin is disconnected, allowing the capacitor to start charging again.
30
This cycle repeats continuously unless the reset input is connected to 0V which forces the output low while reset is 0V. An astable can be used to provide the clock signal for circuits such as counters. A low frequency astable (< 10Hz) can be used to flash an LED on and off, higher frequency flashes are
too fast to be seen clearly. Driving a loudspeaker or piezo transducer with a low frequency of less than 20Hz will produce a series of 'clicks' (one for each low/high transition) and this can be used to make a simple metronome.
Fig. Wave forms representing duty cycle Duty cycle:
The duty cycle of an astable circuit is the proportion of the complete cycle for which the output is high (the mark time). It is usually given as a percentage. For a standard 555/556 astable circuit the mark time (Tm) must be greater than the space time (Ts), so the duty cycle must be at least 50 %: Duty cycle =
Tm R1 + R2 = Tm + Ts R1 + 2R2
To achieve a duty cycle of less than 50% a diode can be added in parallel with R2 as shown in the diagram. This bypasses R2 during the charging (mark) part of the cycle so that Tm depends only on R1 and C1:
31
Tm = 0.7 × R1 × C1 (ignoring 0.7 V across diode)
Ts = 0.7 × R2 × C1 (unchanged)
Duty cycle with diode =
Tm R1 = Tm + Ts R1 + R2
Use a diode such as 1N4148.
Fig.555 Astable circuit with diode across R 2
Applications of Astable 555 Timer: •
Modulate transmitters such as ultrasonic and IR transmitters.
•
Create an accurate clock signal (Example: There is a pulse accumulator pin on the 68HC11 microcontroller that counts pulses. You can apply an astable 555 timer circuit set at 1 Hz frequency to the pulse accumulator pin and create a seconds counter within the microcontroller. The pulse accumulator will be c overed in later in the course).
•
Turn on and off an actuator at set time intervals for a fixed duration. du ration.
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Chapter 7 Piezoelectric sensor Introduction:
Over the past 50 years piezoelectric sensors have proven to be a versatile tool for the measurement of various processes. Today, they are used for the determination of pressure, acceleration, strain or force in quality assurance, process control and development across many different industries. Piezoelectric sensors rely on the piezoelectric effect, which was discovered by the Curie brothers in the late 19th century. While investigating a number of naturally occurring materials such as tourmaline and quartz, Pierre and Jacques Curie realized that these materials had the ability to transform energy of a mechanical input into an electrical output. More specifically, when a pressure [piezo is the Greek word for pressure] is applied to a piezoelectric material, it causes a mechanical deformation and a displacement of charges. Those charges are highly proportional to the applied app lied pressure [Piezoelectricity]. Many creatures creatures use an interestin interesting g application application of piezoelectr piezoelectricity icity.. Bones act as force sensors. Once loaded, bones produce charges proportional to the resulting internal torsion or displacement. Those charges stimulate and drive the build up of new bone material. This leads to the strengthening of structures where the internal displacements are the greatest. With time, this allows allows weaker weaker struct structure uress to increa increase se their their streng strength th and stabil stability ity as materi material al is laid laid down down proportional to the forces affecting the bone. From the Curies’ initial discovery, it took until the 1950‘s before the piezoelectric effect was used used for indust industri rial al sensin sensing g applic applicati ations ons.. Since Since then, then, the utiliz utilizati ation on of this this measur measuring ing pri princ ncip iple le has has expe experi rienc enced ed a cons consta tant nt grow growth th and and can can nowad nowaday ayss be rega regard rded ed as a matu mature re technology with an outstanding inherent reliability. It has been successfully used in various critical applications as for example in medical, aerospace and nuclear instrumentation.
33
Figure 1: Piezoelectricity of quartz
A quartz (SiO2) tetrahedron is shown. When a force is applied to the tetrahedron (or a macroscopic crystal element) a displacement of the cation charge towards the center of the anion charges occurs. Hence, the outer faces of such a piezoelectric element get charged under this pressure. 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/mm2. Even though piezoelectric sensors are electromechanical systems that react on 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 excell excellent ent linear linearit ity y over over a wide wide ampli amplitude tude range. range. Additi Additional onally ly,, piezoe piezoelect lectric ric technol technology ogy is insens insensiti itive ve to electr electroma omagnet gnetic ic field fieldss and radiat radiation ion,, enabli enabling ng measur measureme ements nts under under harsh harsh
34
conditions. Some materials used (especially gallium phosphate or tourmaline) have an extreme stability over temperature enabling sensors to have a working range of 1000°C. Comparison of sensing principles:
Prin Princi cipl plee Stra Strain in Sens Sensit itiv ivit ity y (V/μ*)
Threshold (μ*)
Span to threshold ratio
5 .0
0.00001
100.00
0.0001
0.0001
2.500
0.001
0.0005
2.000
0.005
0.0001
750.00
Piezoelectric
Piezoresistive
Inductive
Capacitive Table 1: Comparison of sensing principles
Comparison of different sensing principles according to Gautschi. Numbers give only a tendency for the general characteristics.
The single disadvantage of piezoelectric sensors is that they cannot be used for true static measurements. A static force will result in a fixed amount of charges on the piezoelectric material. Working with conventional electronics, not perfect insulating materials, and reduction in internal sensor resistance will result in a constant loss of electrons, yielding an inaccurate signal. Elevated temperatures cause an additional drop in internal resistance; therefore, at higher temperatures, only piezoelectric materials can be used that maintain a high internal resistance. Anyhow, it would be a misconception that piezoelectric sensors can only be used for very fast processes or at ambient conditions. In fact, there are numerous applications that show quasistatic measurements while there are other applications that go to temperatures far beyond 500°C.
Principle of Operation:
35
Depending on the way a piezoelectric material is cut, three main types of operations can be distinguished 1. Transversal effect
2. Longi Longitu tudi dinal nal effe effect ct 3. Shear effect.
Figure 2: Gallium phosphate sensing elements A gallium gallium phosphate phosphate crystal is shown with typical typical sensor elements manufactured manufactured out of it. it. Dependi Depending ng on the design design of a sensor sensor differe different”m nt”modes odes”” to load load the crystal crystal can be used: used: transversal, longitudinal and shear (arrows indicate the direction where the load is applied). Charges are generated on both ”x sides” of the element. The positive charges on the front side are accompanied by negative charges on the back.
Transverse effect:
36
A force is applied along a neutral axis and the charges are generated along the d11 direct direction ion.. The amount amount of charge charge depends depends on the geometr geometrical ical dimens dimension ionss of the respect respective ive piezoelectric element. When dimensions a, b, c apply: Cy= -d11 x Fy x b/a
Where a is the dimension in line with the neutral axis and b is in line with the charge generating axis.
Longitudinal effect:
The amount amount of charge chargess produc produced ed is strict strictly ly propor proportio tional nal to the applied applied force force and is independent of size and shape of the piezoelectric element. Using several elements that are mechanicall mechanically y in series and electrical electrically ly in parallel parallel is the only way to increase increase the charge output. The resulting charge is: Cx=d11 x Fx x n Where d11 = piezoelectric coefficient [pC/N] Fx = applied Force in x-direction [N] n = number of elements
Shear effect:
Again, Again, the charges charges produce produced d are strict strictly ly propor proporti tional onal to the applied applied forces forces and are indepe independe ndent nt of the elemen element’s t’s size and shape. shape. For n element elementss mechani mechanicall cally y in series series and electrically in parallel the charge is: Cx=2 x d11 x Fx x n
In contrast to the longitudinal and shear effect, the transverse effect opens the possibility to fine tune sensitivity depending on the force applied and the element dimension. Therefore, Piezo Piezo crysta crystall sensor sensorss almost almost exclus exclusive ively ly use the trans transver verse se effect effect since since it is possib possible le to reproducibly obtain high charge outputs in combination c ombination with excellent temperature behavior.
37
Sensor design:
Based on piezoelectric technology various physical dimensions can be measured, the most important include pressure and acceleration. Figure 3 shows schematic configurations of those sensors in the transverse configuration. In both designs, the elements are thin cuboids that are loaded along their longest extension. For pressure sensors, a thin membrane with known dimensions and a massive base is used; assuring that an applied pressure specifically loads the elements in one direction. For accelerometers, a seismic mass is attached to the crystal elements. When the accelerometer experiences a motion, the invariant seismic mass loads the elements according to Newton’s second law of o f motion. F=m*a Where F is force, m is mass, a is acceleration
(a)
(b)
Figure 3: Schematic sensor design of pressure (a) and acceleration sensors (b) In both piezoelectric pressure sensors (a) and piezoelectric accelerometers (b), the crystal elements are used in transversal mode. The main difference in the working principle between these two cases is the way forces are applied to the sensing elements. In a pressure sensor a thin
38
membrane is used to guide the force to the elements, in accelerometers the forces are applied by an attached seismic mass. Sensors often tend to be sensitive to more than one physical dimension. Therefore, it sometimes becomes necessary to compensate for unwanted effects. For instance, sophisticated pressure sensors often use acceleration compensation elements. Those compensations are based on thefact that the measuring elements may experience both, pressure and acceleration events. A second measuring unit is added to the sensor assembly that only experiences acceleration events. By carefully matching those elements, the acceleration signal (coming from the compensation element) is subtracted from the combined signal of pressure and acceleration (coming of the measuring elements) to derive the true pressure information. Piezoelectric energy harvesting:
The The piezoelectric effect converts mechanical strain into electric current or voltage. This strain can come from many different sources. Human motion, low-frequency seismic vibrations, and acoust acoustic ic noise noise are everyda everyday y example examples. s. Except Except in rare rare instan instances ces the piezoel piezoelect ectric ric effect effect operates in AC requiring time-varying inputs at mechanical resonance to be efficient. Most piezoelectric electricity sources produce power on the order of milli watts, too small for system application, application, but enough for hand-held hand-held devices such as some commercial commercially ly available available self-winding wristwatches. One proposal is that they are used for micro-scale devices, such as in a device harvesting micro-hydraulic energy. In this device, the flow of pressurized hydraulic fluid fluid drives drives a reciprocati reciprocating ng piston piston supported supported by three piezoelectric piezoelectric elements which convert the pressure fluctuations into an alternating current. As piezo energy harvesting has been investigated only since the late '90s, it remains an emerging technology. Nevertheless some interesting improvements were made with the self powered electronic switch at INSA School of engineering, implemented by the spin-off Arveni. In 2006, the proof of concept of a battery-less wireless doorbell push button was created, and recently, a demonstrator showed that classical TV infra-red remote control can be powered by a piezo harvester. Other industrial applications appeared between 2000 and 2005 to harvest energy from vibration and supply sensors for example, or to h arvest energy from shock. Piez Piezoe oele lect ctri ricc syst system emss can can conv conver ertt moti motion on from from the the huma human n body body into into elec electr tric ical al power. DARPA has funded efforts to harness energy from leg and arm motion, shoe impacts, 39
and blood pressure for low level power to implantable or wearable sensors. The nano brushes of Dr. Zhong Lin Wang are another example of a piezoelectric energy harvester. They can be integrated into clothing. Careful design is needed to minimize user discomfort. These energy harvesting sources by association have an impact on the body. The Vibration Energy Scavenging Project Project is another project project that is set up to try to scavenge electrical electrical energy from environmental environmental vibrations and movements. Finally, a millimeter-scale piezoelectric energy harvester has also already been created. The use use of piezoelectric mate materi rial alss to harv harves estt powe powerr has alre alread ady y becom becomee popul popular ar.. Piezoelectric materials have the ability to transform mechanical strain energy into electrical charge. Piezo elements are being embedded in walkway to recover the "people energy" of footsteps. They can also be embedded in shoes to recover "walking energy". Materials:
Two main groups of materials are used for piezoelectric sensors: piezoelectric ceramics and single single crysta crystall materi materials als.. The cerami ceramicc materi materials als (e.g. (e.g. PZT cerami ceramic) c) have have a piezoe piezoelect lectric ric constant /sensitivity that are roughly two orders of magnitude higher than those of single crystal materials and can be produced by an inexpensive sintering process. Unfortunately, their high sensit sensitivi ivity ty is always always combin combined ed with with a lack lack of long long term term stabil stabilit ity. y. Theref Therefore ore,, piezoe piezoelect lectric ric ceramics are very often used wherever the requirements for measuring precision are not too high. The less sensitive single crystal materials (quartz, tourmaline and gallium phosphate) have a much higher – when carefully handled, almost infinite – long term stability. Additionally, some of them show excellent temperature behavior (especially gallium phosphate and tourmaline).
40
Figure 4: Piezoelectric coefficient vs. temperature Piezoelectric coefficient of GaPO4 and quartz are shown versus temperature. Gallium phosphate offers better temperature characteristics and better temperature behavior for many of its material constants including the piezoelectric coefficient, which is a measure for sensitivity.
Specifications: Standard Products :
Item Operating Temperature range
Range -10 ~ 60 °C
Storage temperature range Acceleration limit
-30 ~ 80 °C 15000m/s2 max.
Construction:
Item Appearance Marking
SPEC No remarkable damage or stains allowed (Visual check) Shape(F) , Inclined Angle(2),Product serial No.
Electrical Performance:
Item
SPEC 41
Test Condition
Voltage sensitivity(Vs) Capacitance(Cp) Insulation resistance Non-linearity Incident angle of sensitivity Axis
0.1mV(m/s2)±15% 220pF±20% 500Mohms min 25KHz min 25±3
100m/s2,1kHz 1Vrms,1kHz 10V DC,after 1min At 500 m/s 2
Mechanical performance:
Item Electrode strength Bending strength
Vibration
Solderability
Solder dering heat resistance
Shock
SPEC No terminal electrode shall be peeled off. No outstanding damage.
Test Method 4.9 N from transverse direction,10±0.5s PC boad deflection distance:1mm(speed 1mm/second) 10±0.5s Thickness of PC board:1.6mm Vs drift:within±10% 10 to 55Hz(1minute sweep), Cp drift:within±10% Amplitude:1.5mm, 2 hours each direction. More than ¾ of the soldering Pre-heat: area of the terminal electrodes 150±10°C,1~2minutes, shall be covered with new sold Soldering:230±5C,3±0.5 s Vs drift:within±10% Reflow soldering once 240 °C Cp drift:within±10% peak, over 220°C 10s max. Pre-heating 140±10°C 1~2min. Vs drift:within±10% 15000m/s2, 0.5msec half Cp drift:within±10% sinusoidal wave, 5 times each direction.
Environmental Performance:
Item Dry heat Cold
SPEC Vs drift:within±10% Cp drift:within±10% Vs drift:within±10% 42
Test Method 85±2°C,500 hours -40±3°C,500 hours
Damp heat Heat cycle
Temperature
Cp drift:within±10% Vs drift:within±10% Cp drift:within±10% Vs drift:within±10% Cp drift:within±10% Vs drift:within±10% Cp drift:within±10%
40±2°C,90 ~ 95%RH,500 hours 40±3°C ~ RT ~ 85±3°CRT 30min 2min 30min 2min 5cycles -10 ~ 60°C
Operating Precautions: Application:
This This piezoel piezoelect ectric ric sensor sensor is design designed ed for use in domest domestic ic electr electric ic applia appliance nces, s, AV. equipm equipment ent,, OA equipm equipment ent,, commun communica icatio tion n equipm equipment ent,, measur measuring ing equipm equipment ent and general general electr electronic onic equipm equipment ent.. Check Check with with us separa separatel tely, y, for use in equipm equipment ent which which needs needs high high reliability.(Such reliability.(Such as automobiles, aircraft, medical equipment and space equipment). Precautions for Handling Precautions for Safety
i.
Fail Fail-s -saf afee Desi Design gn for for Equi Equipm pmen ent: t: In appl applic icat atio ion n of the the piez piezoe oele lect ctri ricc sens sensor or,, it is recommended that equipment shall be protected by adding a protective and/or retarding design circuit against deterioration and failures of the piezoelectric sensor.
ii. Operat Operating ing Temperat Temperature ure Ranges Ranges Preheati Preheating ng temper temperatu ature re : 175 o C.This C.This piezoelec piezoelectr tric ic sensor shall not be operated beyond the specified “Operating Temperature Range”in the Specifications. iii. Changes/Dri Changes/Drifts fts in Voltage Sensitivity Sensitivity:It :It shall be noted that voltage voltage sensitivity sensitivity of the piezoelectric sensor may drift depending IC applied (the type names, the manufacturer) and resistance values of external resisters resisters and the the circuit design. iv. Stray Stray Capacitance: Capacitance: Stray capacitance capacitance and insulation insulation resistance resistance on printed circuit board may cause abnormalities of the piezoelectric sensor such as the voltage sensitivity and the freque frequency ncy charac character terist istic. ic. Attent Attention ion shall shall be paid paid to those those abnorma abnormalit lities ies above above mentioned in circuit design.
43
v. Direct Direct Voltage Voltage Avoid directl directly y applying applying a direct direct voltage voltage to the piezoelect piezoelectric ric sensor. sensor.
Prohibited Applications
i.
“Flow “Flow Solderin Soldering g ”shall ”shall not be applied applied to the the piezoelec piezoelectric tric sensor. sensor.
ii. “Ultrasoni “Ultrasonicc Cleaning ”and “Ultraso “Ultrasonic nic Welding Welding ”shall not be applied applied to the piezoelectric piezoelectric sensor for preventing them from electrical failures and mechanical damages. iii. Avoid water water washing washing after solderi soldering. ng. Application Notes
1. Handl Handlin ing g prec precau auti tion onss a) Abnormal/excess electrical stresses such as over voltage spikes and electrostatic discharges may cause electrical deterioration's and failures of the piezoelectric sensor and affect reliability of the devices.b) If the product is drooped or a strong stress is applied to it, it may break.Do not use the products which strong stress has been applied. 2. Automa Automated ted Assembl Assembly y For automat automatic ic insertin inserting, g, make sure sure to make insertin inserting g checks checks by means of the inserting machine in advance. In inserting the product, unsuitable chucking force or inserting speed may apply so excessive impulse to break the product.Avoid inserting using mechanical-chuck-type inserting machine. Also, for the inserting machine using other method, select the low speed. 3. Soldering Soldering in PC PC boards boards and and washing washing after after soldering soldering a) The The produ product ct is appl applic icabl ablee to refo refold ld sold solder erin ing. g. Condi Conditi tion onss of the the sold solder erin ing g temperature and time are recommended. i.
Preh Prehea eati ting ng tem tempe perat ratur uree : 175 175oC oC
ii. Prehea Preheatin ting g time time : 1~2 minute minutess iii. Soldering Soldering temperatur temperaturee : 220oC 220oC
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iv. Solder Soldering ing time time : 20 20 sec max. max. v. Peak Peak temp temper erat atur uree : 250oC 250oC max max.. a) Take care that that a soldering soldering iron iron does not not contact contact with the the product body body (out case). For manual soldering,the maxmimum soldering temperature and time should be 300C and seconds. b) RosinRosin-bas based ed and non-act non-activa ivated ted solderin soldering g flux flux is recommen recommended ded.. The content content of halogen in the flux shall be 0.1 wt. or less. c) Post
Soldering
Cleaning
Application
of
ultrasonic
cleaning
is
prohibited.Cleaning conditions such as kinds of cleaning solvents, immersion times and temperatures etc.Shall be checked by experiments before production. 1. Mainte Maintenan nance ce and and using using enviro environme nment: nt: Avoid maintenance and use in the following environments. i.
Corros Corrosive ive gase gaseous ous atmo atmosphe spheres res (Cl2 (Cl2 , NH3 NH3 , SO2 SO2 , Ox etc.) etc.)
ii. ii. Dust Dusty y plac places es iii. Places Places exposed exposed to direct direct sunlight sunlight iv. Places Places over which water is splashe splashed d v. To be be expos exposed ed direc directl tly y to water. water. vi. Places Places expos exposed ed to briny briny air. air. vii. Places apt to be affected by static electricity or electric electric field strength. 1. Long Term Storag StorageThe eThe piezoelect piezoelectric ric sensor shall shall not be stored stored under severe severe conditio conditions ns of high temperatures and high humidifies.Store them indoors under 40oC max, and 75% RAH max. Use them within one year and check the solder ability before use. And avoid maintenance and use in the following environments.
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i.
Corros Corrosive ive gase gaseous ous atmo atmosphe spheres res (Cl2 (Cl2 , NH3 NH3 , SO2 SO2 , Ox etc.) etc.)
ii. ii. Places Places expos exposed ed to dire direct ct sunli sunlight ght iii. Places Places where dew dew is apt exposed exposed to condense condense The design is subject to change for improvement of quality.
Chapter 8 Circuit diagram and Working: Circuit diagram:
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Fig: Circuit of Knock alarm using piezo electric material
Working:
The circui circuitt of KNOCK KNOCK ALARM ALARM uses uses a thin thin piezoe piezoelect lectric ric plate, plate, senses senses the vibrat vibration ion generated on knocking a surface (such as a door or a table) to activate the alarm and can also be used to safeguard motor vehicles. The piezoelectric plate is used as the sensor. It consist IC 555 Timer to which speaker is connected connected at the output. output. Piezoelect Piezoelectric ric material is used at the input in order to convert any mechanical vibration into electrical variation. When someone knocks on the door, the piezoelectric sensor generates an electrical signal, which is amplified by transistors T1, T2 , T3. The amplified signal is rectified using the Diode and resistor connected in parallel to each other and then this rectified output is filtered to produce a low-level DC voltage, which is further amplified by the remaining transistors T5, T6. The final output from the collector of PNP transistor T6 is applied to reset pin 4 of 555 Timer that is wired as an astable multi vibrator. Whenever the collector of transistor T6 goes high, the astable multi vibrator activates to sound an alarm through the speaker. When the circuit receives an input signal due to knocking, the alarm gets activated activated for about 7 seconds. A led is placed at the output of the IC 555 Timer. The circuit operates off a 9V or a 12V battery.
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Working Flowchart:
Chapter 9 Conclusion Result:
Whenev Whenever er a mechan mechanica icall input input is given given as the input input for piezoelec piezoelectri tricc materi material al those those variations converted into electrical variations and when it is interfaced with a circuit which amplifies, rectifies, filters those signals and buzzer is produced.
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Fig: circuitry of knock alarm using piezoelectric material on breadboard
Advantages: • • • • • • • •
Simple circuitry. Cheap in cost. Highly reliable. No need of micro controllers. Can be operated under +9 Volts or +12Volts. Piezo electric sensor used in the circuitry can hand le high temperature of the order 80°C. Easily operated. It uses readily available, low-cost components.
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Applications: • • •
Can be used as protective shield to the locker to avoid the robbery. Used as door bells. Can be used to safeguard motor vehicles.
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