A technical student is expected to do some experimentation and research work on the subject, which he had learnt, at the classes during the course of his studies . Such an effort when well organized with a definite aim or purpose is called a PROJECT.The object of a project is to evolve technical thinking ,analyse the problem , search for the solution , work in a team , present the findings to the

Professors and above all make a logical Engineer .Through a project student displays his spirit of inquisitiveness , creativity , ability to understand a problem and analytical ways of solving the problem

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1. Introduction 2.Principle of Project 2.1 Circuit Design 2.2 Component Selection 2.3 Component Description

3.Project Development 3.1 PCB Preparation 3.2 PCB Testing 3.3 Assembling of the Unit 4.Testing of the Project Model 5.Result of the test 6. Cost Estimate of the Project 7.Conclusion 8.References

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INTRODUCTION

Rain Alarm ProjectWater is basic need in every one’s life. Saving and proper usage of water is very important. Here is an easy project which will give the alarm when there is rain, so that we can make some actions and save the rain water. As a result, we can increase the water levels of underground water by using underwater recharge technique. Rain water detector will detect the rain and make an alert; rain water detector is used in the irrigation field, home automation, communication, automobiles etc. Here is the simple and reliable circuit of rain water detector which can be constructed at low cost.

Rain Alarm Project Block Diagram:

Rain water sensor is the main component in the circuit. For this rain sensor, no need to go and buy in the market or online. We can do it ourselves just by taking the piece of

Bakelite or mica board and aluminum wire. Bakelite or mica board should be made completely flat and aluminum wire should be pasted on the flat board as shown in the figure below of rain water sensor. Care should be taken that there should be no spaces between the wire and board. When the rain water sensor is completed, it should get connected to the circuit and voltage should be passed through the wires.

Rain water sensor diagram is shown below:

If there is no rain, the resistance between the wires will be very high and there will

be no conduction between the wires in the sensor. If there is rain, the water drops will fall on the rain sensor which will also decrease the resistance between the wires and wires on the sensor board will conduct and trigger the NE555 timer through the transistors circuitry.  Once NE555 is triggered, it will make the output pin high and which will make the buzzer to make alarm.

Rain Alarm Project Circuit Diagram:Rain water detector alarm circuit is shown below.

Circuit Explanation: The points A and B of the circuit are connected to the

points A and B of the rain sensor respectively. When rain

is falling, the rain water will fall on the rain sensor which

has aluminum wires on mica or Bakelite sheet. Due to the

water on sensor, the aluminum wire ‘w’ develops

resistance and gets conducted because of battery

connector, the sensor and also to the circuit.

When the aluminum wires are connected, the transistor

Q1will get turned on and make LED to glow and also Q2

will also be turned ON. When the Q2 is saturated, the

capacitor C1 will be shorted and make the transistor Q3

to be turned ON. C1 will get charged by the resistor R4.

The reset pin of 555timer which is connected to the

emitter of Q3 will be made positive when Q3 reaches to

the saturation mode.

The 555 timer is configured in astable mode. When the

reset pin of the 555 timer is made positive because of

saturation mode of Q3, it will generate the pulse at the pin

3 and make speaker to ring alarm. Capacitor is

connected in between the pin 3 of 555 timer and speaker

because to block the DC signal and allow only the

variations in the signal which make the speaker to make

sound. The diode D2 will not allow any reverse current

from the timer.

Because of the resistor R4 and capacitor C1, Q3 will

get in cut-off after sometime and make the reset pin of

555timer in negative and speaker will stops making

sound. The time for 555timer to make speaker sound

depends on the values of C1 and R4.

When there is no rain, the aluminum wire of the sensor

will not have any resistance or conduction cannot trigger

the circuit.

Note:

Rain senor should be kept in the open place at 30 to

40 degrees from the ground. As a result, rain water will

not present on the sensor for long time.

This circuit will automatically switch of the alarm after

sometime and LED will glow continuously until the rain

stops.

DESIGN OF POWER SUPPLY CIRCUIT :

The Power is given to the transformer

which steps down the input voltage to 10 times less i.e.

20 V .This low voltage is fed to bridge rectifier which

rectifies the ac waveform to dc wave form with some

ripples .These ripples are filtered through capacitance

filter and is fed to linear regulator .The output of

regulator is further filtered to produce clean DC

Voltage. The different linear regulator are used to

produce different voltages i.e. +5V.+15V,-5C,-15V.

78M15

Transformer Rectifier Filter Regulator

POWER SUPLLY CIRCUIT BOARD

COMPONENT SELECTION

Selection of Transformer

To generate a voltage of +15 Volt we have

selected a transformer whose input is 230 V +/-10 %

and output is 9-0-9 Volts and deliver the current up to

500mA.

Selection of Rectifier Diodes

The rectifier diodes of 1Amp rating has been

chosen to keep the safety factor of 100%.

Selection of Filters

Since the load is not high we have chosen the

capacitive filtering to avoid the ripple . To keep the

cost low and sufficient ripple we chose the

Capacitor value.

Selection of R

The resistance has been selected of sufficient

wattage to avoid overheating and of correct value.

Selection of Capacitor

Capacitors have been used for filtering the noise

at the control voltage and for minimizing the ripple.

Selection of Relay

To switch 15V to astable multivibrator small

current relay of SPDT type is used. we have chosen the

relay whose contact current is around 1 Amp. and

holding current is less than 20 mA.

Selection of Speaker

We have chosen 8 ohm 10 Watt speaker.

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DESCRIPTION OF COMPONENTS

RESISTORS:

These are current resisting devices . These

are made of carbon , metallic wire wound etc. These

are read through this acronym BBROYGBVGW. This

stands for ,Black ,Brown , Red, Orange,

Yellow ,Green ,Blue , Violet, Gray and ,White

respectively .These colours are printed as lines on the

resistor the first and second colour lines indicate the

number corresponding to colour .The number indicated

by the colour are shown in table below .The third

line indicate the number of zeros ,the fourth line

indicate the percentage of tolerance of the resistor

BLACK 0 YELLOW 4 GRAY 8

BROWN 1 GREEN 5 WHITE 9

RED 2 BLUE 6 Gold 5%

ORANGE 3 VIOLET 7 Silver 10%

e.g.Red ,Red ,Black Gold = 22 +/-5% ;

Red Red Brown = 220 ; Red Red Red = 2200 ;

Red Red Orange = 22K;Red Red Yellow = 220 K;

Red Red Green = 2.2M ;Red Red Yellow = 22 M

These are available in various wattages like

1/4W ,1/2 W,1 W,2W,5W,10W,20W,50W,100W,200W.

In electronics most common use is up to 5Watt. Higher

the wattages bigger the sizes. The value and wattage

of resisters are to be selected as per the applications.

The tolerence in variation of the rated value is also

selected as per the applications. The resisters are

fabricated directly on the IC itself.

DIODES

These devices allows to flow current in

only one direction . These devices are also called

unidirectional devices .Earlier these devices were

made of vacuum tubes, now a days these are semi

conductor solid state devices. These are PN junction

devices .The PN means doping of the semi conductor

with positive and negative electronic valence atoms .

The silicon diodes have knee voltage drop of 0.7

volts i.e. forward biased voltage drop whereas

germanium diodes have 0.3 voltage drop. The different

diodes are used for different purposes. The diodes

work in forward biased condition or reverse biased

conditions.

These are available with different current

rating , voltage rating , power rating and are used for

different applications. The diodes of higher wattages

are of bigger sizes. The Symbol of Diode and the

ideal curves of diodes are shown below.

current

voltage

Doide Symbol ideal curve

Current

Forward Region

Break Down Voltage

V

oltage Knee Voltage =0.7V

Reverse Region

Diode Characteristics

Diodes are of different types like

Photodiode ,Varactor diode, Schotkey Diode ,PIN

diode ,Zener Diode etc.

Zener Diode

Small signal and rectifier diodes are never

operated in the break down region because this may

damage them. The zener diode is made to operate in

breakdown region , sometimes called breakdown diode.

The zener diode is the back bone of voltage regulators ,

Symbol of Zener Diode

circuits that hold the load voltage almost constant

despite large changes in the line voltage and load

resistance.

Light Emitting Diode

In a forward biased diode , free electrons

cross the junction and fall in to holes. As these electrons

fall from a higher to a lower energy level , they

radiate energy .In ordinary diodes this energy goes off

in the form of heat .But in the light emitting diode

(LED) the energy radiates as light.LEDs that radiate red,

green, yellow, blue, orange or infrared are

manufactured by using elements like gallium, arsenic,

and phosphorous. LEDs that produce visible radiations

are useful with instruments , calculators etc. The

infrared LED finds application in burglar systems and

other areas requiring invisible radiations. The seven

segment displays uses 7 LEDs .

The symbol of LED

TRANSFORMERS:

This are the devices which converts the

primary ac voltage to different secondary ac

voltages .If the secondary voltage is higher then

primary voltage then the transformer is called step

up transformer , if the secondary is less then

primary voltage then it is called step down

transformer , if secondary is same as primary

voltage then it is called unity transformer .This unity

transformer is also used as isolation transformer . This

devices are highly efficient upto 99.9%. i.e. very low

power loss.

The transformers are required for making

dc supply , tuning circuit etc. The current rating of

primary and secondary winding determines the SWG

gauge of the copper wire.

CAPACITORS

This are the storage devices but has in buit

Resistance that’s why the storage voltage does not last

for longer period. The use of capacitor is for tuning the

circuit, filtering the noise to ground, creating the timing

pulse as in our case .The capacitors can not be

fabricated on Ics because of the technical difficulty.

The different values of capacitor that are

available are 1pf,2pf,2.2pf,100pf,200pf,1000pf,0.001uf,

0.01uf,0.1uf,2uf,10uf,22uf,33uf,47uf,56uf, 68uf, 82uf,

100uf,220uf,330uf etc The capacitors are selected based

on capacitance and voltage rating .Higher the voltage

higher the size of the capacitor. These are available in

following types

Electrolytic Capacitor

These capacitors have electrolyte as the

dielectric between the two plates. These are available

with polarity + and -.These are available with vertical

mount or horizontal mount configuration.

Paper CapacitorL: These capacitors are available in

low range of capacitance. The paper is used as dieletric

media between the two plates.

Mica Capacitor: These capacitors are also available in

low range of capacitance. The mica is used as dieletric

media between the two plates.

Disc Capacitor: These are available from 1pF to

1ooooUF

RELAYS

These are electromagnetic devices which

makes or breaks the contact as per the control voltage.

there are solid state relays which do not consume

much power for their operation , but are not available in

higher current rating . Relays are being substituted by

SCRs also called thyrister for on/off control

PROJECT

DEVELOPMENTPREPARATION OF THE PCB

Schematic Preparation Schematic is a circuit that is drawn

either with the help of software or by manually on

paper with standard symbols. If the circuit is big and

complicated then multi layer schematic is made

otherwise single layer schematic is made . The

schematic is drawn with coloured pen to indicate

the different layers , power lines , signal lines and

ground lines.

Artwork Preparation

After making the schematic on a

paper , same is duplicated on transparent acrylic

plastic sheet . This circuit is called artwork . The

artwork is made either bigger or smaller or same

size of the desired PCB .The artwork is drawn with

different colour tapes to identify the signal lines,

power lines and ground lines . The artwork should be

proper without leaving any connection or making any

excess connection or shorts .

Film Making The artwork is reduced or enlarged or made of same size of the PCB on the film through the camera . The camera produces both the positive and negative films . These films are used to made PCB .

Etching of copper claded board The films are put on copper claded

board and the board is exposed to light. The time of

exposure depends on many factors. After the exposure

of the board it is rinsed in the etching solution.

During this etching operation the exposed copper

gets dissolved in the solution whereas unexposed

copper remains intact with the board .This unexposed

copper in turn makes the pattern what we see on

PCB. The board is then washed in water with gentle

brush .

Driling of holes The PCB is now ready for drilling

operation .The holes are now drilled at all places

wherever the components are to be put .The size of

the drills should not be either more then the required

or less then the required . If the hole is large the it will

be difficult to solder and lot of lead will be consumed.

If the hole is small then component will not be

inserted easily.

Tinning of pcb The PCB is tinned after putting the mask

on PCB .This is done to insulate the patterns and

avoid any short. The mask covers the areas where

the soldering is to be done.

PCB TESTING

PCB is checked for all interconnections

through multimeter , whether the tracks are broken or

short at any place , thereby correction is done through

soldering.

ASSEMBLING OF THE UNIT

Components are assembled in proper direction

and avoid the touching of the components to one

another. Heatsink is to be put wherever required with a

heat sink compound. After assembling the components ,

they are soldered and thereafter cleaned with CTC

liquid.

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TESTING OF THE COMPLETE UNIT

The power is given to the circuit

through the switch and the chain is connected. The

chain is disconnected , the siren starts and continues

to remain on till the power is switched off or for one

hour as set the by monostable multivibrator whichever

is earlier. This process continues as long as power is

given to this device and the chain is broken .If the chain

is not broken the siren is not blown.

Hence the unit is tested and work to our

satisfaction .

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COST ESTIMATE

S.NO

Required Material with full Spec.

Reqd Qty.

Cost /unit

Total Cost

1. Speaker 8 ohm 10 watt 1 50.00 50.00

2. Ckt. assembly casing 1 25.00 25.00

3. The external casing 1 50.00 50.00

4. Diode 5 2.00 10.00

5. Resistor 2 2.00 4.00

6. Potentiometer 1 3.00 3.00

7. Capacitors 220uF/63V 1 25.00 25.00

8. Relay 2 35.00 70.00

9. IC Bases 1 15.00 15.00

10. IC NE555/NE556 2 35.00 70.00

11. IC Regulator 78L15 1 30.00 30.00

12. Chain 1 15.00 15.00

13. Power Switches 1 20.00 20.00

14. Voltage Transformer 1 45.00 45.00

15. Cu Claded board 1 60.00 60.00

16. Etching Solutions ½ Litre 150.00 75.00

17. Dilute HCL ½ Litre 160.00 80.00

18. Insulation Coating 1/4 Litre 60.00 15.00

19. Heat sink for regulator 2 30.00 60.00

20. Soldering Iron 1 45.00 45.00

21. Drilling Machine 1 130.00 130.00

22. Multimeter 1 300.0 300.00

23. Testers 1 15.00 15.00

24. Desoldering Pump 1. 75.00 75.00

25. Fluxes 50 gms 35.00 35.00

26. Soldering lead 50 gms 40.00 40.00

27. Wires 10 Meter 2.00 20.00

TOTAL COST OF THE PROJECT 1382.00

Applications of Rain Alarm Project:

1. In the irrigation, it will detect the rain and immediately

alert the farmer.

2. In automobiles, when the rain detector detects the rain

it will immediately active the wipers and inform to the

driver.

3. In communications, it will boost the power of the

antenna and increase the signal strength to send or

receive the signals.

4. In normal house hold, with the help of rain water

detector we can automatically save the rain water.

(This can be done only when home automation is done

and equipment to save the rain water. In this, rain

water detector will detect the rain and helps to switch

ON the equipment which will automatically save rain

water for different purposes).

5. This can also be used if there is a chemical rain also.

This is very common in industrial areas.

CONCLUSION

With the use of the circuits we can develop

many application and solve our day to day problems. In this

circuit the sound of the siren can be increased by using the

audio power amplifier.

The chain need not be of steel , it can be any thin

wire as well. But we can use the steel chain as well , it will

serve double purpose ,first it is difficult to break secondly if it

broken it will raise the alarm .

We can use this device at many places whether in

traveling or at security of the houses /residential areas.

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REFERENCES

1.Electronic Principle by

Albert Paul Malvino

2.Electronics Devices and circuits by

Allen Mottershead.

3.Digital Computer Fundamentals By

Thomas C.Bartee

4.Digital Principles and Applications By

Albert Paul Malvino and Donold P . Leach

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