INTRODUCTION

1.1 Proximity sensor

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the

nominal range or means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and

lack of physical contact between sensor and the sensed object.

Proximity sensors are also used in machine vibration monitoring to measure the variation in distance between a shaft

and its support bearing. This is common in large steam turbines, compressors, and motors that use sleeve-
type bearings.

1.2 Ultrasonic sensors

Ultrasonic sensors (also known as transceivers when they both send and receive) work on aprinciple similar to

radaror sonar which evaluate attributes of a target by interpreting the echoes fromradio or sound waves respectively.

Ultrasonic sensors generate high frequency sound waves andevaluate the echo which is received back by the

sensor. Sensors calculate the time intervalbetweensending the signal and receiving the echo to determine the

distance to an object.

DEPARTMENT OF ECE,LMCST Page1

2.BACKGROUND OF THE PROJECT

2.1 Ultrasound
Ultrasound is asound pressure wave with a frequency greater than the upper limit of human hearing. Ultrasound is

thus not separated from "normal" (audible) sound based on differences in physical properties, only the fact that

humans cannot hear it. Although this limit varies from person to person,it is approximately 20 kilohertz (20,000 hertz)

in healthy, young adults. The production of ultrasound is used in many different fields, typically to penetrate a medium

and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the

innerstructure of the medium, a property also used by animals such as bats for hunting. The most wellknown

application of ultrasound is its use in sonography to produce pictures of fetuses in the human womb. There are a vast

number of other applications as well.

2.2Proximity Detector
Theses are devices that are used to detect the presence of another object using some property such as Doppler

Effect,Mutual Capacitance,reflection of signals etc.These devices and its principles are used in parking

sensors,burglar alarms,motion sensors,RADAR,SONAR etc.


3.BASIC PRINCIPLE

Sonar (originally an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation (usually

underwater, as insubmarine navigation) to navigate, communicate with or detect objects on or under the surface of the

water, such as other vessels.

Active sonar uses a sound transmitter and a receiver. When the two are in the sameplace it is monostatic operation.

When the transmitter and receiver are separated it isbistatic operation . When more transmitters ( or more receivers

) are used , againspatially separated, it is multistatic operation. Most sonars are used monostaticallywith the same

array oftenbeing used for transmission and reception. Activesfields maybe operatedmultistatically.

Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections (echo) of the pulse. This

pulse of sound isgenerally created electronically using a sonar projector consisting of a signal generator,

poweramplifier and electro-acoustic transducer/array. A beamformer is usually employed to concentrate the acoustic

power into a beam, which may be swept to cover the required search angles.


4.OBJECT OF STUDY
Design a reliable circuit.
To implement the ultrasonic proximity detector

5.FIELD OF PROJECT
The present project relates to ultrasonic proximity detector systems. It relates to a collision sensing system for the

Visually impaired ,automotive vehicles, obstruction sensing etc .While the present project deals with the mere

detection of obstruction,it is understood that the project potential is not limited thereto.Those of ordinary skill in the

art and accessto the teachings provided herein will recognize additional modification,application and embodiments

within the scope thereof.

6.DESCRIPTION RELATED ART
The existing proximity detectors generate an ultrasonic wave and transmit this wave with tranducers.The distance to

an object is measured based on the pulse of ultrasonic wave leaves thetranducer and an echo has been received

from the obstacle.The distance is displaye in numbers or LED indicators and an annunciator is activated.

7.MARKET RESEARCHES

In the moving world,movement detection is of equal concern.this can be met with the help of motion or proximity

detectors that operate at ultrasonic frequencies.These are called ultrasonic proximity detectors.Here the device is

installed at the area of interest and any motion within the interested area can be easily detected.

It can be used in museums to describe articles exhibited.Once the viewer approaches the article and when he reach

the field of detector,it detects a motion towards the article .Thus output can be stored data given out in the form of

speech.Installing them in a room or near the door to check babies moving out of sight.

Also in private areas to inform any kind of intrusion.


8.REVIEW OF LITERATURE

Sources of information for the literature were many ,but the main sources being internet reports ,journal,magazines
and other documents .

As the background for executing the project requiredsound knowledge of preliminary design and critical
design,documents dealt with the basis in design of various elements,Knowledge of the components helped in
theeffectiveimplementation of this project.

9.METHODOLOGY
The methodology that has been followed in this project include

Choice of required components.
Analysis of the circuit requirements.
Implementation and testing.

10.PCB FABRICATION
The laser printout of the layout was taken on a transparency and was transferred to the clad sheet by ironing. The
toner used for printing is etching resistant. Then it is washed in ferric chloride solution containing small amount of
hydrochloric acid. After complete removal of the unwanted copper on the trackside, it is taken out from the solution,
washedthoroughly with water and cleaned with thinner .Then holes for the components are placed in their proper
places in the PCB and soldered .Finally ,PCB is fitted to the cabinet using screws.

PCB fabrication involves the following steps.

 The layout of the PCB is drawn on ULTIBOARD .This is transferred to Mylar sheet. This sheet is touched with
black ink.
 The solder side of the Mylar sheet is placed on the shiny side of the star sheets and is placed in a frame. It is then
exposed to sunlight, with Mylar sheet facing the sunlight.
 The exposed five star data sheet is put in hydrogen peroxide solution. It is then put in hot water and shook till
unexposed region become transparent.
 This is put in cold water and then the rough side is stuck onto the screen. This is then pressed and dried well.
 The plastic sheet of the five star sheets is removed leaving the pattern on the screen.
 Acid resistant ink is spread on the screen so that pattern of tracks and pad is obtained on the copper clad sheet.
It is dried.
 The unwanted resist ink is removed using the the sodium solution, holes are drilled.


11.SOLDERING
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler
metal (solder) into the joint, the filler metal having a lower melting point than the workpiece. Soldering differs
from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a
higher temperature, but the workpiece metal does not melt.

Solder
Solder is a fusible metal alloyused to join together metal workpieces and having a melting point below that of

thework pieces.

Flux
The role of a flux in joining processes is typically dual dissolving of the oxides on the metal surface, which

facilitates wetting by molten metal, and acting as an oxygen barrier by coating the hot surface, preventing its

oxidation. in some applications molten flux also serves as a heat transfer medium, facilitating heating of the joint

by the soldering tool or molten solder

Soldering Iron

A soldering iron is a hand toolused in soldering. It supplies heat to melt the solder so that it can flow into the joint

between two workpieces.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by

passing an electric current (supplied through an electrical cord or battery cables) through a resistive heating element.

Soldering process
 Make the layout of the component in the circuit. Plug in the cord of the soldering iron into the main to get it
heated.
 Straighten and clean the component leads using a blade or a knife. Apply a little flux on the leads. Take a little
solder on the soldering iron and apply the the molten solder on the leads.Care must be taken to avoid the
components getting heated up.
 Mount the components on the PCB by bending the leads of the components. Use nose pliers.
 Apply flux on the joints. Soldering must be done in minimum time to avoid dry soldering and heating up of
components.
 Wash the residue using water and brush.


12. SYSTEM DESIGN

Transmitter section

o Resistors:10K,4.7K Pot,3.3K(2)
o Capacitors:47µF,0.001µF
o Tranducer:Ultrasonic transducer transmitter
o Timer IC :555 Timer
o Transistors:BC 327,BC 337.

Receiver Section
o Resistor-680Ω,390KΩ ,470K pot,4.7MΩ,1MΩ(4),4.7MΩ,270KΩ,12KΩ,2KΩ
o Capacitors-0.47µF 25V,0.001µF(2)
o Ultrasonic Transducer Receiver
o Comparator:LM 324
o Diode:IN4148

Output Section

o LED


13.BLOCK DIAGRAM

Comparator Detection
40 KHz Oscillator
Device(LED))

Low Pass Filter
Amplifier

Amplifier

RX1

TX1

Transmitter Section Receiver Section


14.BLOCK DIAGRAM EXPLANATION

TRANSMITTER SECTION

OSCILLATOR : This is basically a wave generating circuit. The transmiter requires an high stablity oscillation. Thus an
oscillation of 40 kHz is maintained.

AMPLIFIER: The output of the oscillator is an ultrasonic frequency signal. Before transmission, the signal is
improved in its strength by amplification. The amplifier converts this signal to a voltage whose level is equivalent to
that can be trasmited.

TRANSMITTER : This is an ultrasonic piezo electric transducer. Its frequency of operation is 40 kHz. The amplified
signal is transmited by ultra sonictrasmitter.

RECEIVER SECTION
Ultrasonic Receiver : The receiver is a piezo electric transducer . The trasmited signal from ultrasonic transmiter is
received by this ultra sonicreceiver . It is internally tuned to 40 kHz.

High Gain Amplifier: The signal obtained from receiver is very feable. This signal has to be amplified to a greater
extend. For this, more than one stage of amplification is done.

Comparator : The output from high gain amplifier is compared with the threshold value of the comparator. The
comparator, thus helps to avoid noise signals and thereby adjusts the range.

Detection Device : The comparator output is connected to the output device. It can be an LED, buzzer, display and
so on.


15.CIRCUIT DIAGRAM

Transmitter Section

Receiver Section


15.CIRCUIT DIAGRAM EXPLANATION

16.1 Oscillator

Standard 555 astable circuit

Inastable mode, the 555 timer puts out a continuous stream of rectangular pulses having a specified frequency.
Resistor R1 is connected between VCCand the discharge pin (pin 7) and another resistor (R2) is connected between the
discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins that share a common node. Hence the
capacitor is charged through R1 and R2, and discharged only through R2, since pin 7 has low impedance to ground
during output low intervals of the cycle, therefore discharging the capacitor.
In the astable mode, the frequency of the pulse stream depends on the values of R1, R2 and C:

[7]

The high time from each pulse is given by:

and the low time from each pulse is given by:

where R1 and R2 are the values of the resistors in ohms and C is the value of the capacitor in farads.

The power capability of R1 must be greater than .
Particularly with bipolar 555s, low values of R1 must be avoided so that the output stays saturated near zero volts
during discharge, as assumed by the above equation. Otherwise the output low time will be greater than calculated
above.
To achieve a duty cycle of less than 50% a diode can be added in parallel with R2 towards the capacitor. This
bypasses R2 during the high part of the cycle so that the high interval depends only on R1 and C.


16.2 Transmitter:
The transmitter that we have used in this application is the 40 T/R 16dB the working is fairly simple. The input from
the emitter section of one of the transistors in the oscillator circuit is fed to the crystal housed in the transducer
causing it to vibrate in one direction. Immediately, thereafter, the applied potential is reversed from the emitter
section of the second transistor in the oscillator circuit. This is supplied continuously from one end the other thus
causing the piezo crystal to vibrate in both directions so as to culminate into the ultrasonic signals in its physical form
i.e., ultrasonic sound waves.

16.3 Receiver
This section utilizes the reverses piezo electric effect in converting the reflected signals from the object converting
them into electrical signal.

16.4 Amplifier:
In order to amplify the signal in the receiver part LM324(N1 and N2) Transistor is used ,which provide gain of 80
each, and wide bandwidth and very low bias current.

16.5 Differential Amplifier

The circuit shown is used for finding the difference of two voltages each multiplied by some constant.

Differential Z in (between two input pins)=R1+R2(Note: this is approximate) for common mode rejection,anything
done to one input must be done to the other. Theaddition of a compensation capacitor in parallel with
Rf,forinstance, must be balanced by an equivalent capacitor in parallel with Rg.


16.6 LED
A light-emitting diode (LED) is a semiconductor light source.LEDs are used as indicator lamps in many devices and
are increasingly used for other lighting. When a light-emitting diode is forward-biased (switched on), electrons are
able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is
called electroluminescence and the colour of the light (corresponding to the energy of the photon) is determined by
the energy gap of the semiconductor. LEDs are often small in area (less than 1 mm2), and integrated optical
components may be used to shape its radiation pattern.[5] LEDs present many advantages over incandescent light
sources including lower energy consumption, longer lifetime, improved robustness, smaller size, and faster
switching. LEDs powerful enough for room lighting are relatively expensive and require more precise current
andheat management than compact fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as aviation lighting, automotive lighting, advertising, general
lighting, and traffic signals. LEDs have allowed new text, video displays, live video, and sensors to be developed,
while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used
in the remote control units of many commercial products including televisions, DVD players, and other domestic
appliances.

16.7 Power Supply
Two Portable and simple 9V battery is used as the Power supply in this circuit.


17.FLOW CHART

Start

ELECRTICAL SIGNALS OF 40KHZ

CONVERT ELECTICAL SIGNALS TO SOUND WAVE

TRANSMIT SOUNDWAVE THROUGH TRANSMITTER

NO IF OBSTRUCTION

YES

RECEPTION OF SOUNDWAVES AFTER REFLECTION

AMPLIFY SOUND SIGNALS

AUDIO FREQUENCY AMPLIFICATION

SIGNAL DETECTION THROUGH LED

STOP


18.WORKING
This ultrasonic proximity detector comprising independent, battery-powered transmitterand receiver sections
makes use of a pair of matched ultrasonic piezoceramic transducers operating at around40kHzeach.Thiscircuitcan
beusedinexhibitionstoswitchonpre- recorded audio/video messages auto-
maticallywhenavisitorevincinginterestinaproductcomesnearanexhibitedproduct.

Transmitter circuit. ComprisesCMOStimerIC555(IC1) configured as anastablemultivibrator, which may be tuned to
the frequency of the ultrasonic piezoceramictransmitter’s resonant frequency of around 40 kHz using preset VR1.
A complementary pair of transistors T1 and T2 is used for driving and buffering thetransducerwhile it draws spikes of
current from IC1 circuit to sustain oscillations and thereby avoids any damage.

The receiver front-end is designed to provide a very high gain for the reflected faint ultrasonic frequency
signals detected by the ultrasonic transducer. The amplifiers built around N1 and N2,
respectively,provideACvoltagegain of around 80 each. These two stages shouldhaveahighopen-circuitgain, wide
bandwidth and very low bias current apart from being capable of single-supply operation. Quad op-amp LM324 isused
here due to its low cost. For higher efficiency, you may usesingleop-ampssuchasCA3130 orCA3140.

When avisitor pauses before a product, it signifies his interest. Switching diode D1 followed by a
filtercomprisingcapacitorC5andresistor R10 is used to meet this requirement. The filter also helps to bypass brief
bursts of ambient noise in the ultrasonic range. The third stage comprising N3 works as a comparator to provide a
triggering ulse when a visitor stops by. This pulse can be used to trigger timer or a monostable, whose out-
putmaythenbeusedtoswitchon the audio/video messageconcerning the product for a predetermined period.

When somebodycomes in front oftheultrasonicpiezoceramictransducer pair, the status LED (LED1) glows because
of the signal reflected fromthebodyofthevisitor. The circuit can be assembled on any general-purpose
PCB. The transmitter and the receiver shouldbealignedsuchthatthetransmitted ultrasonic signal is optimally received
by the receiver after reflection.


19.APPLICATIONS

The ultrasonic proximity detector is used for the following applications:

 Blind spot monitor

 Parking sensors

 Lane departure warning system.

 Pre-crash system

 For non-destructive testing

 Sensors for liquid level control.

 Sensing clear objects.

 Applications not suitable for photoelectric application


20.FUTURE ENHANCEMENTS

Present device can be enhanced to perform a wider range of applications such as non destructive testing, provide

distance measurement, etc. apart from present day applications, the future would see this device being used

among the activities related to deep earth explorations. Here the device is equipped with imaging devices that

can withstand the rigors of unknown underground.

21.ADVANTAGES

 Circuit simplicity

 Convenient to use

 Easily portable

 Affordable cost

 Long-lasting life & also reliable

 Generally, the frequency of the beep indicates distance from an obstruction with the beeps becoming faster

the closer the vehicle moves to an object. A continuous tone may be heard when the vehicle is extremely

close, often warning the person to stop immediately to avoid collision

 No physical contact with the object to be detected. Hence no friction & hence no wear & tear. Also unlimited

operating cycles

 They are not affected by target color or atmospheric dust, snow etc

 Can work in adverse conditions

 Targets can be detected in solid , liquid granular or powder state

 Sensing distance is more compared to inductive or capacitive proximity sensors


22.DISADVANTAGES

 While using this device, avoid the company of your pets. The reason is that pets can hear only

ultrasonic sound, which will irritate them and they will bark unnecessarily.

 Since the system relies on the reflection of sound waves, it may not detect some items that are not

flat or large enough to reflect sound, for example a narrow pole or a longitudinal object pointed

directly at the vehicle or near an object

 Medium dependent

 Cannot detect objects in the range of few millimetres


23.ESTIMATION AND COST

Components Quantity Cost(Rs)

IC 555 1 5
IC324 1 10
BC 327 1 1
BC 337 1 1
390K Ω 1 1
680Ω 1 1
10K 1 1
4.7K 1 1
3.3K 2 1
47µF 1 1
0.001µF 2 2
470K pot 1 10
1M Ω 4 1
4.7M Ω 1 1
390K 1 1
470K 1 1
4.7M 1 1
1M 3 1
270K 1 1
12K 2 1
0.47µ 1 2
IN4148 1 2
LED 2 2
switch 1 2
Ultrasonic txr/rxr 1 250
9v battery 2 40
TOTAL 341


24.CONCLUSION

The aim of this project to develop a cost effective, affordable & convenient tool to detect the presence of a visitor

in front of exhibit item in the museum.

The circuit uses basic component such as transistor, resistors and integrated circuits to function as devices which

provide oscillations, amplification and counting. Further enhancements, such as addition of

microprocessor can extend the project’s application.

25.BIBLIOGRAPHY

 Articles from: Electonics For You February 2006

 KatiraieKamyar. Adjustable , Ultrasonic Collision Warning System U.S patents, January
1993,Patent No:5347273

 Auld .B.A Acoustic Fields & Waves in solids, Vol-1 & 2, 2nd edition Krieger Publishing Company, Feb
1990

 Linear Integrated Circuits-Dr.RoyChoudary,Shail B Jain.

 www.4share.com

 www.scribd.com

 www.electronics.com

 www.fairchildsemi.com

 www.wikipedia.com

 www.electronicsforyou.com

26.APPENDIX


26.1 PCB Layout of Transmitter and Receiver

Receiver

Transmitter


26.2 Component Layout

Receiver

Transmitter


26.3 Components on PCB

26.4 Final Product


26.5 COMPONENTS DESCRIPTION
26.5.1 Resistor

A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit
element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in
direct proportion to that voltage.
The reciprocal of the constant of proportionality is known as the resistance R, since, with a
Given voltage V, a larger value of R further "resists" the flow of current I as given
byOhm'slaw:

I=(V/R)

Resistors are common elements of electrical networks and electronic circuits and areUbiquitous 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). Resistors are also implemented within integrated circuits, particularly
analog devices, and can also be integrated into hybrid and printed circuits.

Resistor colour code system


26.5.2 Capacitors
A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in
an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical
conductors separated by a dielectric (insulator); for example, one common construction consists of metal foils
separated by a thin layer of insulating film. Capacitors are widely used as parts of electrical circuits in many common
electrical devices.
When there is a potential difference (voltage) across the conductors, a static electric field develops across the
dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in
the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads.
This is the ratio of the electric charge on each conductor to the potential difference between them.
Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass,
in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to
particular frequencies, in electric power transmission systems for stabilizing voltage and power flow, and for many
other purposes.
Ideal Capacitance C is given by ,C=Q/V,where Q is the ratio of charge between plates and V is the voltage.

26.5.3 Diodes
A diode is a two-terminal electronic component with asymmetric transfer characteristic, with low (ideally
zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other. A semiconductor
diode, the most common type today, is a crystalline piece ofsemiconductor material with a p-n junction connected to
two electrical terminals.

The most common function of a diode is to allow an electric current to pass in one direction (called the
diode's forward 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, including extraction of modulation from radio signals in radio
receivers—these diodes are forms of rectifiers.


26.5.4 IN4148 Diode
The 1N4148 is a standard silicon switching diode. Its name follows the JEDEC nomenclature. The 1N4148 has a DO-
35 glass package and is very useful at high frequencies with a reverse recovery time of no more than 4ns.

26.5.5 Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of
a 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 higher than the controlling (input) power, a transistor can amplify a
signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

BC327

It’s a PNP general purpose transistor having features of high current (max 500mA) and Low voltage(max
45V).Used for general purpose switching and amplification, especially in driver and output stages of audio
amplifiers.


BC337

BC337 is a NPN epitaxial silicon transistor used in switching and amplifier Applications .It is suitable for AF-
Driver stages and low power output stages and it is the compliment of BC327.

26.5.6OP-amp Voltage Comparator
An operational amplifier (op-amp) has a well balanced difference input and a very high gain. This parallels the
characteristics of comparators and can be substituted in applications with low-performance requirements.[4]
In theory, a standard op-amp operating in open-loop configuration (without negative feedback) may be used as a
low-performance comparator. When the non-inverting input (V+) is at a higher voltage than the inverting input (V-),
the high gain of the op-amp causes the output to saturate at the highest positive voltage it can output. When the
non-inverting input (V+) drops below the inverting input (V-), the output saturates at the most negative voltage it
can output. The op-amp's output voltage is limited by the supply voltage. An op-amp operating in a linear mode with
negative feedback, using a balanced, split-voltage power supply, (powered by ± VS) its transfer function is typically
written as: . However, this equation may not be applicable to a comparator circuit which is
non-linear and operates open-loop (no negative feedback).


26.5.7INTEGRATED CIRCUITS

LM324
This device consist of four independent high-gain frequency-compensated operational amplifiers that are designed
specifically to operate from a single supply over a wide range of voltages. Operation from split supplies also is
possible if the difference between the two supplies is 3 V to 32 V (3 V to 26 V for the LM2902), and V CC is at least 1.5
V more positive than the input common-mode voltage. The low supply-current drain is independent of the
magnitude of the supply voltage.

Applications include transducer amplifiers, dc amplification blocks, and all the conventional operational-amplifier
circuits that now can be more easily implemented in single-supply-voltage systems.

Pin Diagram:


Pin Description:

Pin No Function Name
st
1 Output of 1 comparator Output 1
st
2 Inverting input of 1 comparator Input 1-
st
3 Non-inverting input of 1 comparator Input 1+
4 Supply voltage; 5V (up to 32V) Vcc
nd
nd
nd
rd
rd
rd
11 Ground (0V) Ground
th
th
th

555 Timer
555 is a very commonly used IC for generating accurate timing pulses. It is an 8pin timer IC and has mainly two
modes of operation: monostable and astable. In monostable mode time delay of the pulses can be precisely
controlled by an external resistor and a capacitor whereas in astable mode the
frequency & duty cycle are controlled by two external resistors and a capacitor.
555 is very commonly used for generating time delays and pulses.

The 555 has three operating modes:

 Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers,
missing pulse detection, bounce free switches, touch switches, frequency divider, capacitance
measurement, pulse-width modulation (PWM) and so on.
 Astable: free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse
generation, logic clocks, tone generation, security alarms, pulse position modulation and so on. Selecting
a thermistor as timing resistor allows the use of the 555 in a temperature sensor: the period of the output pulse
is determined by the temperature. The use of a microprocessor based circuit can then convert the pulse period
to temperature, linearize it and even provide calibration means.
 Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no
capacitor is used. Uses include bounce-free latched switches.


Pin Diagram:

Pin Description:

Pin No Function Name
1 Ground (0V) Ground
2 Voltage below 1/3 Vcc to trigger the pulse Trigger
3 Pulsating output Output
4 Active low; interrupts the timing interval at Output Reset
5 Provides access to the internal voltage divider; default 2/3 Vcc Control Voltage
6 The pulse ends when the voltage is greater than Control Threshold
7 Open collector output; to discharge the capacitor Discharge
8 Supply voltage; 5V (4.5V - 16 V) Vcc

26.5.8Transducers
Ultrasonictransceivers or transducers work on a principle similar to radar or sonar which evaluates attributes of a
target by interpreting the echoes from radio or sound waves respectively. The sensors generate high frequency
sound waves and evaluate the echo which is received back by the sensor. This technology can be used for measuring
wind speed and direction, fullness of tank and speed through air orwater, ultrasonography etc., Systems typically use
a transducer which generatessound waves in the ultrasonic range by turning electrical energy into sound which can
be then measured and displayed. The technology is limited by the shapes of the surface and density or consistency
of the material. For example, foam on the surface of the fluid in a tank


26.5.9 LED

Miniature size LED of 5cm is used
]
Miniature size LED usually do not use a separate heat sink. Typical current ratings ranges from around 1 mA to above
20 mA. The small size sets a natural upper boundary on power consumption due to heat caused by the high current
density and need for a heat sink.

Common package shapes include round, with a domed or flat top, rectangular with a flat top (as used in bar-graph
displays), and triangular or square with a flat top. The encapsulation may also be clear or tinted to improve contrast
and viewing angle.

There are three main categories of miniature single die LEDs:

 Low-current — typically rated for 2 mA at around 2 V (approximately 4 mW consumption).
 Standard — 20 mA LEDs at around 2 V (approximately 40 mW) for red, orange, yellow, and green, and 20 mA at
4–5 V (approximately 100 mW) for blue, violet, and white.
 Ultra-high-output — 20 mA at approximately 2 V or 4–5 V, designed for viewing in direct sunlight.
Five- and twelve-volt LEDs are ordinary miniature LEDs that incorporate a suitable series resistor for direct connection
to a 5 V or 12 V supply.


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