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

Abstract

1

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.

2

Contents:

1) Introduction

2) Block Diagram

3) Resistors and Capacitors

4) Transistors

5) Diode

6) Integrated Circuit

i. 555 Timer

a) Inputs of 555

b) Output of 555

c) Loud Speaker

d) Relay coils and other inductive loads

e) 555 Astable mode

f) Astable Operation

g) Duty Cycle

7) Piezoelectric Sensor

i. Introduction

ii. Comparison of sensing principles

iii. Principle Of Operation

a) Transverse effect

b) Longitudinal effect

c) Shear effect

iv. Sensor Design

v. Piezoelectric energy harvesting

vi. Materials

vii. Specifications

a) Standard products

b) Construction

c) Electric performance

d) Mechanical performance

e) Environmental performance

3

viii. Operating Precautations

a) Applications

b) Precaution for handling

i. Precautions for safety

ii. Prohibited applications

iii. Application notes

8) Circuit diagram and Working

9) Conclusion

i. Results

ii. Advantages

iii. Applications

4

Chapter 1

Introduction

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

convert any mechanical vibration into electrical variation, it avoids false triggering. 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. When the circuit receives an input signal due to knocking,

the alarm gets activated for about 7 seconds. 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.

5

Chapter 2

6

Block Diagram

Piezo Electric Sensor

Amplifier Rectifier

FilterAmplifier555 Timer

Speaker and LED

Piezoelectric Sensor:

A piezoelectric sensor is a material which converts mechanical variations and electrical

variations.

Amplifier:

Amplifier is a device which increases the strength of the 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.

(Uni-directional).

Filter:

Filter is a device which minimize the ripple content (or) fluctuations 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.

7

Chapter 3

Resistors and Capacitors

Resistors:

Introduction

A resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current through it in accordance with Ohm's law:

V = IR

Resistors are elements 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, the tolerance, the maximum working voltage and the power rating. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical 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.

8

Resistors can be integrated into hybrid and printed 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.

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.

9

This formulation is often used in practice. For example, if V is 12 volts and R is 400 ohms, a current of 12 / 400 = 0.03 amperes will flow through the resistance R.

Resistors used in Knock Alarm using piezoelectric material Circuitry:

i. 100 Ω

ii. 470 Ω

iii. 1 K Ω

iv. 3.3 K Ω

v. 10 K Ω

vi. 22 K Ω

vii. 47 K Ω

viii. 82 K Ω

ix. 220 K Ω

x. 330 K Ω

xi. 1 M Ω

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.

Capacitors are occasionally referred to as condensers. This is now considered 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

10

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, usually copper, electrodes are separated by a vacuum. The insulating

envelope is usually glass or ceramic. Typically of low capacitance - 10 - 1000 pF and high

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 from high quality polymer film (usually polycarbonate, polystyrene,

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:

11

Similar to metal film, often high voltage, suitable for high frequencies, expensive,

excellent tolerance.

Paper:

Used for relatively high voltages. Now obsolete.

Glass:

Used for high voltages, expensive, stable temperature coefficient in a wide 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

(especially the class 2) high dissipation factor, high frequency coefficient of dissipation, their

capacity depends on applied voltage, and their capacity changes with aging. However they find

massive use in common low-precision coupling and filtering applications, suitable for high

frequencies.

Aluminum electrolytic:

Polarized, constructionally similar to metal film, but the 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.

12

Super capacitors:

Made from carbon aerogel, carbon nanotubes, or highly porous electrode materials.

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.

Capacitors used in this project are:

0.01 µF

0.1 µF

22 µF

47 µF

100 µF

13

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.

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

revolutionised the field of electronics, and paved the way for smaller and cheaper radios,

calculators, and computers, amongst other things.

A bipolar junction transistor (BJT) is a three-terminal electronic device constructed of

doped semiconductor material and may be used in amplifying or switching 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 different charge concentrations. This mode of operation is contrasted with unipolar

14

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.

Introduction

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 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

make holes the majority carrier in the base.

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

15

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

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

related by the current–voltage relation of the base–emitter junction, which is just the usual

exponential current–voltage curve of 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.[1][2][3] Detailed models of transistor action, such as the Gummel–Poon model,

account for the distribution of this charge explicitly to explain transistor behavior more exactly. [4]

The charge-control view easily handles phototransistors, where minority carriers in the base

region are created by the absorption of photons, and handles the dynamics of turn-off, or

recovery time, which depends on charge in the base region recombining. However, because base

16

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.

In analog circuit design, the current-control view is sometimes used because it is

approximately linear. That is, the collector current is approximately βF 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) model is

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, design for circuits such as differential amplifiers again becomes a mostly

linear problem, so the voltage-control view is often preferred. For translinear circuits, in which

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 design is 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 Bipolar transistor exhibits a few delay characteristics when turning on and off. 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 represented by βF or hfe; it is

approximately the ratio of the DC collector current to the DC base current in forward-active

17

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, 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 0.998. Alpha and beta are more precisely related by the following identities (NPN

transistor):

Structure

Fig Simplified cross 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 n type, p type and n type in a NPN transistor. Each semiconductor region is

connected to a terminal, appropriately labeled: emitter (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

18

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.

NPN transistors consist of a layer of 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. In other terms, an NPN transistor is "on" when its base is pulled high 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)

19

Chapter 5

Diode

Introduction:

In electronics, a diode is a two-terminal electronic component that conducts electric

current in only one direction. The term usually refers to a semiconductor diode, the most

common type today. This is a crystalline piece of semiconductor material connected to two

electrical terminals.[1] A vacuum tube diode (now little used except in some high-power

technologies) is a vacuum tube with two electrodes: a plate and a cathode.

Fig: Diode

The most common function of a diode is to allow an electric current to pass in one

direction (called the diode's forward bias direction) while blocking current in the opposite

direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a

check valve. This unidirectional behavior is called rectification, and is used to convert 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), to electronically tune radio and TV receivers (varactor diodes), to generate radio

frequency oscillations (tunnel diodes), and to produce light (light emitting diodes). Tunnel diodes

exhibit negative resistance, which makes them useful in some types of circuits.

20

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 is high-speed switching diodes fabricated in planar technology, and

encapsulated in hermetically sealed leaded glass SOD27 (DO-35) packages.

21

Chapter 6

Integrated circuit

Introduction

In electronics, an integrated circuit (also known as IC, chip, or microchip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as 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 integrated circuit is a miniaturized electronic circuit constructed of 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 circuits using electronic components. The integrated circuits mass production capability, reliability, and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of designs using discrete transistors.

22

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.

23

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 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. 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.

24

A 555 Timer can be operated under following modes:

Astable - Producing a square wave

Monostable - Producing a single pulse when triggered

Bistable - A simple memory which can be set and reset

Buffer - An inverting buffer (Schmitt trigger)

The timer basically operates in one of the two modes—monostable (one-shot)

multivibrator or as an astable (free-running) multivibrator. In the monostable 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 Timer

Definition of 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.

25

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

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 the desired output pulse width, the input trigger should effectively be shortened 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 precaution with respect to the trigger input concerns storage time in the lower

comparator.This portion of the circuit can exhibit normal turn-off delays of several microseconds

after triggering; that is, the latch can 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

trigger current, must also flow from this terminal into the external circuit. This current is

typically 500nA (nano-amp) and will define the upper limit of 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 Q21 and Q22 provide drive for source-type loads, and their Darlington

26

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, for instance, the low state Vce(sat) is typically 0.25 volts at 5 mA. Operating at 15 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. The state of the output pin will always reflect

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. [see "Pin 2 - 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

27

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 flip-

flop 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

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 voltage-

controlled 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

28

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 Mega-

ohm. 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

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 off-

state 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 Vcc) 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

operate essentially the same over this range of voltages without change in timing period.

Actually, the most significant operational difference is the output drive capability, which

increases for both current and voltage range as the supply voltage is increased. Sensitivity of

29

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 astable circuit produces a 'square wave' , this is a digital waveform with 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'.

Fig.: 555 Timer circuit

The time period (T) of the square wave is the time for one complete cycle, but it is usually better

to consider frequency (f) which is the number of cycles

per second.

30

T = 0.7 × (R1 + 2R2) × C1 and f = 1.4

(R1 + 2R2) × C1

Where,

T = Time period in seconds (s)

f = Frequency in hertz (Hz)

R1 = Resistance in ohms ( )

R2 = Resistance in 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 × (R1+R2) × C1

Space time (output low):

Ts = 0.7 × R2 × C1

Many circuits require Tm and Ts to be almost equal; this is achieved if R2 is much larger than R1.

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 duty cycle below.

Choosing R1, R2 and C1:

31

R1 and R2 should be in the range 1k to 1M . It is best to choose C1 first because capacitors are

available in just a few values.

Choose C1 to suit the frequency range you require (use the table as a guide).

Choose R2 to give the frequency (f) you requires. Assume that R1 is much smaller than

R2 (so that Tm and Ts are almost equal), then you can use:

R2 = 0.7/f×C1

Choose R1 to be about a tenth of R2 (1k min.) unless you want the mark time Tm 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 variable it must have a

fixed resistor of at least 1k in series

(this is not required for R2 if it is

variable).

Fig. Table of different frequencies of 555 Timer

32

555 astable frequencies

C1R2 = 10kR1 = 1k

R2 = 100kR1 = 10k

R2 = 1MR1 = 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 6.8Hz0.68Hz(41 per min.)

0.068Hz(4 per min.)

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.

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.

33

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:

Tm = 0.7 × R1 × C1 (ignoring 0.7 V across diode)

Ts = 0.7 × R2 × C1 (unchanged)

34

Duty cycle with diode = Tm

= R1

Tm + Ts R1 + R2

Use a diode such as 1N4148.

Fig.555 Astable circuit with diode across R2

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 covered in later in the course).

Turn on and off an actuator at set time intervals for a fixed duration.

35

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 pressure [Piezoelectricity].

Many creatures use an interesting application of piezoelectricity. 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 weaker structures to increase their strength and stability as material is laid 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 for industrial sensing applications. Since then, the utilization of this measuring

principle has experienced a constant growth and can nowadays be regarded as a mature

technology with an outstanding inherent reliability. It has been successfully used in various

critical applications as for example in medical, aerospace and nuclear instrumentation.

36

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

excellent linearity over a wide amplitude range. Additionally, piezoelectric technology is

insensitive to electromagnetic fields and radiation, enabling measurements under harsh

37

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:

Principle Strain Sensitivity(V/μ*)

Threshold(μ*)

Span tothresholdratio

Piezoelectric 5.0 0.00001 100.00

Piezoresistive

0.0001 0.0001 2.500

Inductive0.001 0.0005 2.000

Capacitive0.005 0.0001 750.00

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 quasi-

static measurements while there are other applications that go to temperatures far beyond 500°C.

38

Principle of Operation:

Depending on the way a piezoelectric material is cut, three main types of operations can be

distinguished

1. Transversal effect

2. Longitudinal effect

3. Shear effect.

Figure 2: Gallium phosphate sensing elements

A gallium phosphate crystal is shown with typical sensor elements manufactured out of

it. Depending on the design of a sensor different”modes” to load the crystal can be 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.

39

Transverse effect:

A force is applied along a neutral axis and the charges are generated along the d11

direction. The amount of charge depends on the geometrical dimensions of the respective

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 of charges 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=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, 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=2 x d11 x Fx x n

40

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 crystal sensors almost exclusively use the transverse effect since it is possible to

reproducibly obtain high charge outputs in combination with excellent temperature behavior.

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 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)

41

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

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 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 acoustic noise are everyday examples. Except in rare instances the piezoelectric 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, but enough for hand-held devices such as some commercially 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 drives a reciprocating piston supported by three 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

42

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 harvest energy from shock.

Piezoelectric systems can convert motion from the human body into electrical

power. DARPA has funded efforts to harness energy from leg and arm motion, shoe impacts,

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 is another project that is set up to try to scavenge electrical energy from environmental

vibrations and movements. Finally, a millimeter-scale piezoelectric energy harvester has also

already been created.

The use of piezoelectric materials to harvest power has already become popular.

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 crystal materials. The ceramic materials (e.g. PZT ceramic) have a piezoelectric

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

sensitivity is always combined with a lack of long term stability. Therefore, piezoelectric

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).

43

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 RangeOperating Temperature range -10 ~ 60 °C

Storage temperature range -30 ~ 80 °CAcceleration limit 15000m/s2 max.

Construction:

Item SPECAppearance No remarkable damage or stains allowed

(Visual check)Marking Shape(F) , Inclined Angle(2),Product serial

No.

44

Electrical Performance:

Item SPEC Test ConditionVoltage sensitivity(Vs) 0.1mV(m/s2)±15% 100m/s2,1kHzCapacitance(Cp) 220pF±20% 1Vrms,1kHzInsulation resistance 500Mohms min 10V DC,after 1minNon-linearity 25KHz min At 500 m/s2

Incident angle of sensitivity Axis

25±3

Mechanical performance:

Item SPEC Test MethodElectrode strength No terminal electrode shall be

peeled off.4.9 N from transverse direction,10±0.5s

Bending strength No outstanding damage. PC boad deflection distance:1mm(speed 1mm/second)10±0.5sThickness of PC board:1.6mm

Vibration Vs drift:within±10%Cp drift:within±10%

10 to 55Hz(1minute sweep),Amplitude:1.5mm,2 hours each direction.

Solderability More than ¾ of the soldering area of the terminal electrodes shall be covered with new sold

Pre-heat: 150±10°C,1~2minutes,Soldering:230±5C,3±0.5 s

Soldering heat resistance Vs drift:within±10%Cp drift:within±10%

Reflow soldering once 240 °C peak, over 220°C 10s max.Pre-heating 140±10°C 1~2min.

Shock Vs drift:within±10%Cp drift:within±10%

15000m/s2, 0.5msec half sinusoidal wave, 5 times each direction.

45

Environmental Performance:

Item SPEC Test MethodDry heat Vs drift:within±10%

Cp drift:within±10%85±2°C,500 hours

Cold Vs drift:within±10%Cp drift:within±10%

-40±3°C,500 hours

Damp heat Vs drift:within±10%Cp drift:within±10%

40±2°C,90 ~ 95%RH,500 hours

Heat cycle Vs drift:within±10%Cp drift:within±10%

40±3°C ~ RT ~ 85±3°CRT30min 2min 30min 2min 5cycles

Temperature Vs drift:within±10%Cp drift:within±10%

-10 ~ 60°C

Operating Precautions:

Application:

This piezoelectric sensor is designed for use in domestic electric appliances, AV.

equipment, OA equipment, communication equipment, measuring equipment and general

electronic equipment. Check with us separately, for use in equipment which needs high

reliability.(Such as automobiles, aircraft, medical equipment and space equipment).

Precautions for Handling

Precautions for Safety

i. Fail-safe Design for Equipment: In application of the piezoelectric sensor, 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. Operating Temperature Ranges Preheating temperature : 175 o C.This piezoelectric

sensor shall not be operated beyond the specified “Operating Temperature Range”in the

Specifications.

46

iii. Changes/Drifts in Voltage Sensitivity:It shall be noted that voltage sensitivity of the

piezoelectric sensor may drift depending IC applied (the type names, the manufacturer)

and resistance values of external resisters and the circuit design.

iv. Stray Capacitance: Stray capacitance and insulation resistance on printed circuit board

may cause abnormalities of the piezoelectric sensor such as the voltage sensitivity and

the frequency characteristic. Attention shall be paid to those abnormalities above

mentioned in circuit design.

v. Direct Voltage Avoid directly applying a direct voltage to the piezoelectric sensor.

Prohibited Applications

i. “Flow Soldering ”shall not be applied to the piezoelectric sensor.

ii. “Ultrasonic Cleaning ”and “Ultrasonic Welding ”shall not be applied to the piezoelectric

sensor for preventing them from electrical failures and mechanical damages.

iii. Avoid water washing after soldering.

Application Notes

1. Handling precautions

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. Automated Assembly For automatic inserting, make sure to make inserting 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.

47

3. Soldering in PC boards and washing after soldering

a) The product is applicable to refold soldering. Conditions of the soldering

temperature and time are recommended.

i. Preheating temperature : 175oC

ii. Preheating time : 1~2 minutes

iii. Soldering temperature : 220oC

iv. Soldering time : 20 sec max.

v. Peak temperature : 250oC max.

b) Take care that a soldering iron does not contact with the product body (out case).

For manual soldering,the maxmimum soldering temperature and time should be

300C and seconds.

c) Rosin-based and non-activated soldering flux is recommended. The content of

halogen in the flux shall be 0.1 wt. or less.

d) 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.

4. Maintenance and using environment:

Avoid maintenance and use in the following environments.

i. Corrosive gaseous atmospheres (Cl2 , NH3 , SO2 , Ox etc.)

ii. Dusty places

iii. Places exposed to direct sunlight

48

iv. Places over which water is splashed

v. To be exposed directly to water.

vi. Places exposed to briny air.

vii. Places apt to be affected by static electricity or electric field strength.

5. Long Term StorageThe piezoelectric sensor shall not be stored under severe conditions

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.

i. Corrosive gaseous atmospheres (Cl2 , NH3 , SO2 , Ox etc.)

ii. Places exposed to direct sunlight

iii. Places where dew is apt exposed to condense

The design is subject to change for improvement of quality.

49

Chapter 8Circuit diagram and Working:

Circuit diagram:

Fig: Circuit of Knock alarm using piezo electric material

Working:

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 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

50

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 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.

Working Flowchart:

51

Mechanical Input(By knocking)Convert input into electric

variation using piezo electric

sensor.Amplify these

signals.Convert the

amplified signal into

unidirectional signal

Start Removing the

unwanted component

sAmplify the

signal

555 Timer gets

activated

High Amplifi

ed signal?

Alarm gets activated

End

Yes

No

Chapter 9

Conclusion

Result:

Whenever a mechanical input is given as the input for piezoelectric material those

variations converted into electrical variations and when it is interfaced with a circuit which

amplifies, rectifies, filters those signals and buzzer is produced.

Fig: circuitry of knock alarm using piezoelectric material on breadboard

52

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 handle high temperature of the order 80°C. Easily operated. It uses readily available, low-cost components.

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.

53