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CHAPTER 2

INTRODUCTION TO PROJECTThis is a simple circuit for water level alarm. It is built around 2 bc547 transistors(T1 and

T2) and 2 IC 555 timer(IC1 and IC2).Both IC1 and IC2 are weird in astable multivibrator

mode. Timer IC1 produces low frequency while timer IC2 produces high frequency. As a

result a beeping tone is generated when the water tank is full. Initially when the tank is

empty, transistor t1 does not conduct. consequently, transistor t2 conducts and pin4 of IC1 is

low. This low voltage disables IC1 and it does not oscillate. The low output of IC1 disables

IC2 and it does not oscillate. As a result, no beeping tone is generated from speaker. Butwhen the tank gets filled transistor T1 conducts. Consequently transistor T2 is cutoff and pin

4 of IC1 becomes high. This high voltage enables Ic1 and it oscillate to produce low

frequency at pin 3. This low frequency output enables Ic2 and it also oscillates to produce

high frequency. As a result sound is produced from speaker .Using a preset at load we can

tune the sound of speaker.

The circuit can be powered from a +9v power supply

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2.1 CIRCUIT DIAGRAM

C 1

1 nD 5

1 N 4 0 0 7

U 3

5 5 5 a l t1

2

3

4

5

6

7

8

G N D

T R I G G E R

O U T P U T

R E S E T

C O N T R O L

T H R E S H O L D

D I S C H A R G E

V C C

+ 9 v

R 51 0 0 k R 6

5 6 k

+ 9 v

D 1

1 N 4 0 0 5 G

C 4

1 n

C 80 . 0 1 u

J P 1

H E A D E R 2

12

0 . 1 u

R 92 2 0 k R 1 0

1 k

C 5. 0 1 u C 6

0 . 0 1 u

+ 9 v

J P 2

H E A D E R 2

12

+ 9 v

R 7

RQ 1B C 5 4 7

1

2

3

+ 9 v

U 2

5 5 5 a l t1

2

3

4

5

6

7

8

G N D

T R I G G E R

O U T P U T

R E S E T

C O N T R O L

T H R E S H O L D

D I S C H A R G E

V C C

+ 9 v

< D o c >

< T i t l e >

B

M o n d a y , J u n e 2 8 ,

T i t l e

S i z e D o c u m e n t N u m b e r

D a t e : S h e e

Q 2B C 5 4 7

1

2

3

+ 9 T 1

T R A N S F O R M E R C T

1 3

6

2 4

J P 3

H E A

12

R 31 KR 4

1 2 k

+ 9 v

0

C 3

1 n

D 2

1 N 4 0 0 7

R 11 0 k

C 7

1 n

D 3

1 N 4 0 0 7

U 1L M 7 8 0 5 C / T O

1 3

2

I N O U T

G

N

D

R 8

1 2 k

R 2

1 k

D 4

1 N 4 0 0 7

Fig 2.1

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CHAPTER 3

PARTS DESCRIPTION

3.1 IC 555 timer

The 555 timer IC is an amazingly simple yet versatile device. It has been around now for

many years and has been reworked into a number of different technologies. The two

primary versions today are the original bipolar design and the more recent CMOS

equivalent. These differences primarily affect the amount of power they require and their

maximum frequency of operation; they are pin-compatible and functionally

interchangeable.

This page contains only a description of the 555 timer IC itself. Functional circuits and a

few of the very wide range of its possible applications will be covered in additional

pages in this category.

Fig 3.1

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The figure shows the functional block diagram of the 555 timer IC. The IC is available

in either an 8-pin round TO3-style can or an 8-pin mini-DIP package. In either case, the

pin connections are as follows:

1. Ground.

2. Trigger input.

3. Output.

4. Reset input.

5. Control voltage.

6. Threshhold input.

7. Discharge.

8. +VCC. +5 to +15 volts in normal use.

The operation of the 555 timer revolves around the three resistors that form a voltage

divider across the power supply, and the two comparators connected to this voltage

divider. The IC is quiescent so long as the trigger input (pin 2) remains at +V CC and the

threshhold input (pin 6) is at ground. Assume the reset input (pin 4) is also at +VCC and

therefore inactive, and that the control voltage input (pin 5) is unconnected. Under these

conditions, the output (pin 3) is at ground and the discharge transistor (pin 7) is turned

on, thus grounding whatever is connected to this pin.

The three resistors in the voltage divider all have the same value (5K in the bipolar

version of this IC), so the comparator reference voltages are 1/3 and 2/3 of the supply

voltage, whatever that may be. The control voltage input at pin 5 can directly affect this

relationship, although most of the time this pin is unused.

The internal flip-flop changes state when the trigger input at pin 2 is pulled down below

+VCC/3. When this occurs, the output (pin 3) changes state to +VCC and the discharge

transistor (pin 7) is turned off. The trigger input can now return to +VCC; it will not affect

the state of the IC.

However, if the threshhold input (pin 6) is now raised above (2/3)+VCC, the output will

return to ground and the discharge transistor will be turned on again. When the

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threshhold input returns to ground, the IC will remain in this state, which was the

original state when we started this analysis.

The easiest way to allow the threshhold voltage (pin 6) to gradually rise to (2/3)+V CC is

to connect it to a capacitor being allowed to charge through a resistor. In this way we

can adjust the R and C values for almost any time interval we might want.

The 555 can operate in either monostable or astable mode, depending on the connections

to and the arrangement of the external components. Thus, it can either produce a single

pulse when triggered, or it can produce a continuous pulse train as long as it remains

powered.

Fig 3.2

In monostable mode, the timing interval, t, is set by a single resistor and capacitor, as

shown to the right. Both the threshhold input and the discharge transistor (pins 6 & 7)

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are connected directly to the capacitor, while the trigger input is held at +VCC through a

resistor. In the absence of any input, the output at pin 3 remains low and the discharge

transistor prevents capacitor C from charging.

When an input pulse arrives, it is capacitively coupled to pin 2, the trigger input. The

pulse can be either polarity; its falling edge will trigger the 555. At this point, the output

rises to +VCC and the discharge transistor turns off. Capacitor C charges through R

towards +VCC. During this interval, additional pulses received at pin 2 will have no

effect on circuit operation.

The standard equation for a charging capacitor applies here: e = E(1 - (-t/RC)). Here, "e" is

the capacitor voltage at some instant in time, "E" is the supply voltage, VCC, and " " is

the base for natural logarithms, approximately 2.718. The value "t" denotes the time that

has passed, in seconds, since the capacitor started charging.

We already know that the capacitor will charge until its voltage reaches (2/3)+V CC,

whatever that voltage may be. This doesn't give us absolute values for "e" or "E," but it

does give us the ratio e/E = 2/3. We can use this to compute the time, t, required to

charge capacitor C to the voltage that will activate the threshhold comparator:

2/3 = 1 - (-t/RC)

-1/3 = - (-t/RC)

1/3 = (-t/RC)

ln(1/3) = -t/RC

-1.0986123 = -t/RC

t = 1.0986123RC

t = 1.1RC

The value of 1.1RC isn't exactly precise, of course, but the roundoff error amounts to

about 0.126%, which is much closer than component tolerances in practical circuits, and

is very easy to use. The values of R and C must be given in Ohms and Farads,

respectively, and the time will be in seconds. You can scale the values as needed and

appropriate for your application, provided you keep proper track of your powers of 10.

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For example, if you specify R in megohms and C in microfarads, t will still be in

seconds. But if you specify R in kilohms and C in microfarads, t will be in milliseconds.

It's not difficult to keep track of this, but you must be sure to do it accurately in order to

correctly calculate the component values you need for any given time interval.

The timing interval is completed when the capacitor voltage reaches the (2/3)+VCC upper

threshhold as monitored at pin 6. When this threshhold voltage is reached, the output at

pin 3 goes low again, the discharge transistor (pin 7) is turned on, and the capacitor

rapidly discharges back to ground once more. The circuit is now ready to be triggered

once again.

Fig 3.3

If we rearrange the circuit slightly so that both the trigger and threshhold inputs are

controlled by the capacitor voltage, we can cause the 555 to trigger itself repeatedly. In

this case, we need two resistors in the capacitor charging path so that one of them can

also be in the capacitor discharge path. This gives us the circuit shown to the left.

In this mode, the initial pulse when power is first applied is a bit longer than the others,

having a duration of 1.1(Ra + Rb)C. However, from then on, the capacitor alternately

charges and discharges between the two comparator threshhold voltages. When

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charging, C starts at (1/3)VCC and charges towards VCC. However, it is interrupted

exactly halfway there, at (2/3)VCC. Therefore, the charging time, t1, is -ln(1/2)

(Ra + Rb)C = 0.693(Ra + Rb)C.

When the capacitor voltage reaches (2/3)VCC, the discharge transistor is enabled (pin 7),

and this point in the circuit becomes grounded. Capacitor C now discharges through Rb

alone. Starting at (2/3)VCC, it discharges towards ground, but again is interrupted

halfway there, at (1/3)VCC. The discharge time, t2, then, is -ln(1/2)(Rb)C = 0.693(Rb)C.

The total period of the pulse train is t1 + t2, or 0.693(Ra + 2Rb)C. The output frequency

of this circuit is the inverse of the period, or 1.44/(Ra + 2Rb)C.

Note that the duty cycle of the 555 timer circuit in astable mode cannot reach 50%. On

time must always be longer than off time, because Ra must have a resistance value

greater than zero to prevent the discharge transistor from directly shorting VCC to

ground. Such an action would immediately destroy the 555 IC.interesting and very

useful feature of the 555 timer in either mode is that the timing interval for either charge

or discharge is independent of the supply voltage, VCC. This is because the same VCC is

used both as the charging voltage and as the basis of the reference voltages for the two

comparators inside the 555. Thus, the timing equations above depend only on the valuesfor R and C in either operating mode.In addition, since all three of the internal resistors

used to make up the reference voltage divider are manufactured next to each other on the

same chip at the same time, they are as nearly identical as can be. Therefore, changes in

temperature will also have very little effect on the timing intervals, provided the external

components are temperature stable. A typical commercial 555 timer will show a drift of

50 parts per million per Centigrade degree of temperature change (50 ppm/C) and

0.01%/Volt change in VCC. This is negligible in most practical applications.

3.2 TRANSISTOR (BC547)

A transistor is asemiconductor device commonly used to amplify or switch electronic

signals. A transistor is made of a solid piece of a semiconductormaterial, with at least

three terminals for connection to an external circuit. A voltage or current applied to one

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VRC = ICE RC, the voltage across the load (the lamp with resistance RC)

VRC + VCE = VCC, the supply voltage shown as 6V

If VCE could fall to 0 (perfect closed switch) then Ic could go no higher than VCC / RC,

even with higher base voltage and current. The transistor is then said to be saturated.

Hence, values of input voltage can be chosen such that the output is either completely

off, or completely on. The transistor is acting as a switch, and this type of operation is

common in digital circuits where only "on" and "off" values are relevant.

3.4 PIEZO ELECTRIC BUZZER

Basically, the sound source of a piezoelectric sound component is a piezoelectric diaphragm.

A piezoelectric diaphragm consists of a piezoelectric ceramic plate which has electrodes on

both sides and a metal plate (brass or stainless steel, etc.). A piezoelectric ceramic plate is

attached to a metal plate with adhesives.0.D.C. voltage between electrodes of a piezoelectric

diaphragm causes mechanical distortion due to the piezoelectric effect. For a misshaped

piezoelectric element, the distortion of the piezoelectric element expands in a radial direction.

The metal plate bonded to the piezoelectric element does not expand.

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CHAPTER 4

PCB DESIGNING

4.1 PRINTED CIRCUIT BOARD

A printed circuit board, or PCB, is used to mechanically support and electrically

connect electronic components using conductive pathways, tracks, ortraces,etched from

copper sheets laminated onto a non-conductivesubstrate. It is also referred to as printed

wiring board (PWB) or etched wiring board. A PCB populated with electronic

components is a printed circuit assembly (PCA), also known as a printed circuit board

assembly (PCBA).

PCBs are inexpensive, and can be highly reliable. They require much more layout effort

and higher initial cost than either wire-wrapped orpoint-to-point constructed circuits,

but are much cheaper and faster for high-volume production. Much of the electronics

industry's PCB design, assembly, and quality control needs are set by standards that arepublished by the IPC organization.

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.Fig 4.1

4.2 LAYOUT

Fig 4.2

4.3 ETCHING

The vast majority of printed circuit boards are made by bonding a layer of copper over

the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing

unwanted copper after applying a temporary mask (e.g. by etching), leaving only the

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desired copper traces. A few PCBs are made by addingtraces to the bare substrate (or a

substrate with a very thin layer of copper) usually by a complex process of multiple

electroplating steps."Additive" processes also exist. The most common is the "semi-

additive" process. In this version, the unpatterned board has a thin layer of copper

already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this

mask exposes those parts of the substrate that will eventually become the traces.)

Additional copper is then plated onto the board in the unmasked areas; copper may be

plated to any desired weight. Tin-lead or other surface platings are then applied. The

mask is stripped away and a brief etching step removes the now-exposed original copper

laminate from the board, isolating the individual traces. Some boards with plated thru

holes but still single sided were made with a process like this. General Electric made

consumer radio sets in the late 1960s using boards like these.

4.4 DRILLING ON BOARD

Holes through a PCB are typically drilled with tiny drill bits made of solid tungsten

carbide. The drilling is performed by automated machines with placement controlled by

a drill tape or drill file. These computer-generated files are also called numerically

controlled drill(NCD) files or "Excellon files". The drill file describes the location and

size of each drilled hole. These holes are often filled with annular rings (hollow rivets)

to create vias. Vias allow the electrical and thermal connection of conductors on

opposite sides of the pcb.Most common laminate is epoxy filled fiberglass. Drill bit wear

is in part due to the fact that glass, being harder than steel on the Mohs scale, can scratch

steel. High drill speed necessary for cost effective drilling of hundreds of holes per board

causes very high temperatures at the drill bit tip, and high temperatures (400-700

degrees) soften steel and decompose (oxidize) laminate filler. Copper is softer than

epoxy and interior conductors may suffer damage during drilling.When very small vias

are required, drilling with mechanical bits is costly because of high rates of wear and

breakage. In this case, the vias may be evaporated by lasers. Laser-drilled vias typically

have an inferior surface finish inside the hole. These holes are called micro vias.It is also

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possible with controlled-depth, drilling laser drilling, or by pre-drilling the individual

sheets of the PCB before lamination, to produce holes that connect only some of the

copper layers, rather than passing through the entire board. These holes are called blind

vias when they connect an internal copper layer to an outer layer, or buried vias when

they connect two or more internal copper layers and no outer layers.The walls of the

holes, for boards with 2 or more layers, are made conductive then plated with copper to

form plated-through holes that electrically connect the conducting layers of the PCB. For

multilayer boards, those with 4 layers or more, drilling typically produces a smear of the

high temperature decomposition products of bonding agent in th

4.5 SOLDERING

Soldering is a process in which two or more metal items are joined together by melting

and flowing a filler metal into the joint, the filler metal having a relatively low melting

point. Soft soldering is characterized by the melting point of the filler metal, which is

below 400 C (752 F). The filler metal used in the process is called solder. Soldering is

distinguished from brazing by use of a lower melting-temperature filler metal; it is

distinguished from welding by the base metals not being melted during the joining

process. In a soldering process, heat is applied to the parts to be joined, causing the

solder to melt and be drawn into the joint by capillary action and to bond to the materials

to be joined by wetting action. After the metal cools, the resulting joints are not as strong

as the base metal, but have adequate strength, electrical conductivity, and water-

tightness for many uses. Soldering is an ancient technique mentioned in the Bible and

there is evidence that it was employed up to 5000 years ago in Mesopotamia.

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Soldering filler materials are available in many different alloys for differing

applications. In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or

60/40, which is almost identical in performance to the eutectic) has been the alloy of

choice. Other alloys are used for plumbing, mechanical assembly, and other

applications.

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Fig 4.3

CHAPTER 5CONCLUSION

In this report, we presented a comprehensive overview of water level alarm circuit.

This circuit gives an alarm when water reaches a specific desired level in the tank.

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It is useful in daily life for conserving and checking of overflow of water.it is very

Useful in multi storey buildings.as no need to go on roof to check the level of water.

It has certain limitation i,e it is not suitable for industrial applications,with further

Modifications it can be used in industries. The project holds great scope for future

Improvements as well.It can be used in flood prone areas by disaster management.

It will give alarming sound when river reaches danger level.with further modifications

it can also control the water pump i,e as soon as water reaches desired level water

pump will be shut automatically.

REFERENCES

[1]. Jain R.P modern digital electronicsTata Mcgraw Hill Publication 2008,

4th edition

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[2]. Gayakwad Ramakant Linear Intergrated Circuits Pearson Publication

2009, 3rd edition

[3]..http://www.electronicsforu.com/electronicsforu/lab/ad.asp?

url=/EFYLinux/circuit/July2009/CI-

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