MAIN OF VAMSI

AQUARIUM PROBE

ABSTRACT

In the present days the most popularly increasing hobby is to maintain a

water aquarium. Maintaining a water aquarium is not an easy task, because a

number of environmental factors may affect the fish culture. If only our tap water

was perfect and if we would be able to maintain same water conditions, then it

would be so much easier. Any change in the water temperature levels of an

aquarium, may cause an adverse effect on the fish health.

Though there are many factors like pH, hardness, alkalinity, the temperature

and others effect the fish culture, among them the temperature has its extreme effect

on the aquarium fish. Because, the healthy growth of fish and its breed will only

possible at necessary temperature conditions (between 24°C and 33°C). So the

temperature reading is an important aspect for the aquarium owner. Hence to monitor

the temperature of the aquarium water we present an internal circuitry of the

temperature sensing device in our project “AQURIUM PROBE”.

The project “AQUARIUM PROBE” aims to monitor the temperature and to

indicate the rise in temperature through the audio and visual indicators. This project

has very practical applications to almost every individual who has a small or large

scale fresh water fish aquarium.

GPCET 1 Department Of ECE

AQUARIUM PROBE

CONTENTS: Page

i. List of Figures 3

ii. List of Tables 4

Chapters

1. Introduction 5

1.1 Block Diagram 7

2. Circuit description 9

2.1 Integrated Circuits 10

2.2 A detail study of IC CA3140 12

2.3 A detail study of IC LM3915 19

2.4 BC 557 and its characteristics 27

2.5 Voltage Regulators 29

2.6 A study about diode 1N34 34

2.7 Bridge Rectifier and its workings 36

3. Circuit Operation 40

4. Applications 44

Advantages

Disadvantages

5. Result 46

Future

6. Conclusion 48

Appendices

A Cost Details 49

B References 50

C Photo copies 51


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Index 53

LIST OF FIGURES

1.1 Block diagram of Aquarium Probe

2.1 Aquarium Probe circuit diagram

2.1.1 Pin diagram of IC CA3140

2.1.2 Block diagram of IC CA3140

2.1.3 Schematic diagram of IC CA3140

2.2.1 Pin diagram of IC LM3915

2.2.2 Block diagram of IC LM3915

2.2.3 Typical Connection of IC LM3915

2.3.1 A picture of BC 557

2.3.2 Pin diagram of BC 5572.6.1: Diode Bridge Rectifier

2.4.1 A picture of Voltage Regulator

2.4.2 Block diagram of Voltage Regulator

2.4.3 Pin diagram of Voltage Regulator

2.4.3 Pin diagram of IC 7805

2.4.4 Pin diagram of IC 7809

2.5.1 A picture of diode 1N34

2.6.1 Diode Bridge Rectifier

2.6.2 Bridge Rectifier with capacitor

2.6.3 Waveforms obtained for the Bridge Rectifier

4.1 Practical application of Aquarium Probe


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LIST OF TABLUR COLOUMNS

1. IC CA3140 and its pin purpose

2. Specifications of IC CA3140

3. IC LM3915 and its pin purpose

4. Specifications of IC LM3915

5. Characteristics of BC 557

6. Absolute Maximum Ratings of VR 78XX series

7. Absolute Maximum Ratings of diode 1N34


AQUARIUM PROBE

Chapter - 1

INTRODUCTION

The environmental conditions have its great effect on the aquarium

fish. Among them the temperature plays an important role for the healthy growing of

fish, because the oxygen level of water depends on the temperature. If the

temperature of the aquarium water increases then the oxygen level of the water will

decrease. That is the temperature is invertly related to the oxygen content in the

water. If the oxygen percentage level in the water is reduced then the fish will effect

greatly.

In early days the Aquarium thermometer is a device used to measure the

temperature of the aquarium water. The Aquarium thermometer not only measures

room temperature but also works in a wide range of applications from air

conditioning units, and green houses to aquariums and refrigerators.

The size of the thermometer makes it ideal for any number of situations where

you need an accurate reading environmental temperature in terms of Celsius. The

wide measurement range makes this thermometer ideal for the home, garage,

aquarium, greenhouse, ice house, and workplace - even the car. But the thermometer

is to be used manually by the person and it cannot automatically indicate the

temperature of the aquarium water and also the thermometer cannot indicate the

temperature beyond the range -50°C ~ 70 °C.

The temperature of the aquarium water may increase at any time which may

affect the fish breed. So it’s an important thing for an owner to measure the aquarium

temperature at different times. Let’s think that you are at some work and if you are

not in a situation to measure the temperature of the aquarium water, and if the

aquarium water is maintained at normal temperature conditions, then there is no effect

on the fish. But if the temperature increases to high ranges, what will happen to the

fish? The fish in the aquarium may die due to the critical temperature conditions.

Hence here is an AQUARIUM PROBE device which indicates the temperature

automatically.


AQUARIUM PROBE

Existing commercial products are very costly and provide many features that

the average aquarium owner may not use. Commercial available features include

password protection, water conductivity, weather simulation, sunrise and sunset

simulation, and ORP (oxidation reduction potential). All of these features are excess

for the average owner. The common man who buys an aquarium with a cost of

Rs.2500, would not able to purchase commercial devices which cost of Rs7,500-

20,000, will become a great burden to him. In order to help the common man, our

product will minimize cost and provide only the basic features needed to successfully

monitor and maintain a fresh water aquarium.


AQUARIUM PROBE

1.1 BLOCK DIAGRAM:

The block diagram of the Aquarium Probe is depicted in the following figure.

Fig 1.1: Block diagram of Aquarium Probe

Block Descriptions:

The block diagram of Aquarium Probe shown in figure 1, has four main

blocks. They are explained below individually in brief.

Input Stage:

The input stage mainly consists of a diode 1N34 and acts as temperature to

resistance converter. It means that this readily available signal diode 1N34 is used in

this block as the temperature sensing probe. As the resistance of this diode depends

on the surrounding temperatures, this diode is said to be the diode sensor.

Inverting Amplifier:

The Inverting Amplifier accepts the voltage that is provided by the input

stage, means the diode 1N34. As the input received from the input stage is very

small, it has


INVERTING AMPLIFIER IC CA3140

INPUT STAGEDIODE 1N34

DISPLAY DRIVER IC LM3915

OUTPUT STAGE

GREEN ANDRED LEDS

PIEZO BUZZER

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to be amplified and hence the IC CA3140 acts as amplifier and amplifies the input

voltage to the required level.

Display Driver:

The output from the inverting amplifier is directly given to the third stage

which drives the output stage. The display driver block consists of IC LM3915,

which is an 18 pin IC. The IC LM3915 drives the outputs depending on the inputs it

received. The small change in the input side of LM3915 can change the output.

Output stage:

The last and the final stage is the output stage, the output stage depends on the

display driver stage. This block consists of majorly two sub blocks they are explained

below.

1. LEDs:

The Light Emitting Diode is an acronym for the LED. The LEDs are used

here to indicate the outputs. The LEDs will glow according to the inputs given by the

Micro Controller. Here we use two LEDs, one for indicating the temperature up to a

range of 350 C and other is to indicate up to a range 350C-500C. When a “danger”

level is reached by any of the parameters, the LEDs will be switched on accordingly.

2. Piezo Buzzer:

The Piezo Buzzer is a type of audio device like an alarm which gives a “Beep”

sound whenever the temperature is reached to critical levels.


AQUARIUM PROBE

Chapter – 2

CIRCUIT DESCRIPTION

The Aquarium probe circuit is quite simple and it majorly consists of two IC’s

which plays a major role in providing the output. Along with these two IC’s the

circuit consists of a transistor and the voltage regulators. The Aquarium probe circuit

diagram is depicted in the figure

Fig 2.1: Aquarium Probe circuit diagram

Before knowing about the operation of the circuit one must gain a brief

knowledge about the elements of the circuit and these are explained in detail in this

chapter. As I mentioned earlier, the IC’s and the VR’s plays a major role, they will be

discussed first and the remaining will be explained in the later topics.


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2.1 INTEGRATED CIRCUITS

The IC’s (acronym for Integrated Circuits) are now ruling the present

generation of electronics, it meant that we cannot imagine the electronic world

without the IC as it is involved in almost every electronic equipment. Hence it’s a

need to know what generally an IC is.

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.

The ICs which are presently in the market are very much developed than that

of the ICs that are in the earlier decades. The IC development did not take place in a

single day by a single person, many experts involved in the development of ICs from

the beginning when the diode is first invented. The history of the IC’s is briefly noted

in the following lines in order to bring some knowledge about the evolution of ICs

from its beginning.

1940s - setting the stage

The initial inventions that made integrated circuits possible. The PN

diode and the Transistor were invented in this decade.

1950s - the invention of the integrated circuit

In this decade the transistor developed and invension of IC took place.

1954 – First commercial silicon transistor

1958 – Integrated circuit invented

1960s - product and technology advances

The advancement technolgy made to ivent the first MOS IC.


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1969 – First commercial IC

1963 – CMOS invented

1969 – BiCOMS invented

1970s - invension of new products

The developments in the CMOS technology lead to the invension of

new products like EPROM, DSP, DRAMs and Microprocessors.

1971 – Microprocessor invented

1978 – Intel 8086/8088

1980s - advancement of technology

The CMOS still developed to EEPROM and Flash and intel

introduced first 32 bit microprocessor.

1982 – Intel 80286

1983 – EPROM invented

1985 - Intel 80386DX

1989 - Intel 80486DXTM

1990s - further refinements in technology

The Intel still developed its microprocesor products, and the number

of transistors used per IC increased rapidly in this decade.

1993 – Intel Pentium

1994 - 64Mbit DRAM

1997 - Intel Pentium IITM

1999 - Intel Pentium IIITM

2000s - technolgy at the supreme

The technolgy rocked like anything in this decade, the Intel introduced

the high speed operating microprocessors like “core 2 duo”.

2000 - Intel Pentium 4TM

2007 - Intel Core 2 Duo

Thus the IC in the electronics became a major part and due to the

advancements in technology the number of transistors per IC is increasing

rapidly.


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2.2 A DETAIL STUDY OF IC CA3140

Back to the study of the Aquarium Probe the circuit mainly has the below

mentioned ICs:

IC CA3140

IC LM3915

IC CA3140:

The IC CA3140 is a 4.5M.Hz BiCMOS Operational amplifier. It combines

the advantages of high voltage PMOS transistors with high voltage bipolar transistors

on a single monolithic chip.

The CA3140, an Op-Amp feature gate protected MOSFET (PMOS) transistors

in the input circuit to provide very high input impedance, very low input current, and

high speed performance. This can be operated at the supply voltages ranging from 4V

to 36V (either single supply or dual supply). The stable operation in unity gain

follower can be achieved by internal phase compensation and additionally they have

access terminal for a supplementary external capacitor if additional frequency roll-off

is required.

The use of PMOS field effect transistors in the input stage results in common

mode input voltage capability down to 0.5V below the negative supply terminal, an

important attribute for single supply applications. The output stage uses bipolar

transistors and includes built-in protection against damage from load terminal short

circuiting to either supply rail or to ground.

Features:

MOSFET input stage

Very high input impedance (Zin) – 1.5TΩ

Very low input current (II) – 10pA at + 15V

Wide common mode input voltage range (VICR) – 0.5V


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It directly replaces the industrial type 741 in most applications.

Pin out:

IC CA3140 is an 8-pin BiMOS operational amplifier as shown below

Figure 2.1.1: Pin diagram of IC CA3140

The CA3140 operate supply voltage from 4V to 36V either in single or dual

supply. The terminals ‘1’ and ‘6’ of CA3140 provides for use in application requiring

input offset voltage nulling.

Pin

NoName Purpose

1 Offset NullOffset null is adjusted to get output as 0v when both the

inputs are same.

2 Inverting Input When the input is low then output is high.

3Non-Inverting

InputWhen the input is high then output is high.

4 V-The Negative supply voltage which must between 0 and

-36V

5 Offset NullOffset null is adjusted to get output as 0v when both the

inputs are same.

6 Output Output pin is to find the output.

7 V+The positive supply voltage which must between 0 and

36V

8 Strobe Strobe is used to enable/disable the device.


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Table 1: IC CA3140 pin name and their purpose

Block Diagram:

The block diagram of CA3140 is shown below

Figure

2.1.2: Block Diagram of IC CA3140

Absolute Maximum Ratings:

The absolute maximum rating values given to a particular IC describes that if

the user crosses the given ratings or stresses then the damage may occur to the IC, so

that it may not work properly. Hence it’s a compulsory need to follow the ratings, the

following are the ratings given for the IC CA3140

Dc Supply Voltage(Between V+ and V- Terminals) - 36V

Differential Mode Input Voltage - 8V

Input Terminal Current - 1mA

Output Short Circuit Duration - Indefinite


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Temperature Range - -55oC to 125oC

Specifications:

The main specifications of CA3140 is as shown in the tabular column

Specifications of CA3140 when VSUPPLY = ±5V, V- =0V, TA = 25oC.

Parameter Symbol Typical Value Units

Input Offset Voltage |VIO| 5 mv

Input Resistance RI 1 TΩ

Input Offset Current |IIO| 0.1 pA

Input Current II 2 pA

Output Resistance RO 60 Ω

Common Mode Input Voltage

RangeVICR -0.5, 2.6 µV

Gain Bandwidth Product fT 3.7 MHz

Slew Rate SR 7 V/µs

Maximum Output Current IOM+, IOM- 10, 1 µs

Large Signal Voltage Gain AOL 100 kV/V

Common Mode Rejection Ratio CMMR 90 dB

Power Supply Rejection Ratio PSRR 80 dB

Max Output Voltage VOM+, VOM- 3, 0.13 V

Supply Current I+ 1.6 mA

Device Dissipation PD 8 mW

Input Offset Voltage Temperature

DriftΔVIO/ΔT 8 μV/oC

Table 2: Specifications of IC CA3140

Schematic Diagram:

The Schematic diagram IC CA3140 consists of 5 stages

1. Bias Circuit


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2. Input Stage

3. Second Stage

4. Output Stage

5. Dynamic Current Sink

Figure 2.1.3: Schematic Diagram of IC CA3140

The schematic diagram depicted in the figure 2.1.3 is explained in the following

lines.

Bias Circuit:

The function of the bias circuit is to establish and maintain constant current

flow through D1, Q6, Q8 and D2. D1 is a diode connected transistor mirror connected in

parallel with the base emitter junctions of Q1, Q2 and Q3.


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Input Stage:

The schematic diagram consists of a differential input stage using PMOS

field-effect transistors (Q9, Q10) working into a mirror pair of bipolar transistors (Q11,

Q12) functioning as load resistors together with resistors R2 through R5. The mirror

pair transistors also function as a differential-to-single-ended converter to provide

base current drive to the second stage bipolar transistor (Q13). Offset nulling, when

desired, can be effected with a 10kΩ potentiometer connected across Terminals 1 and

5 and with its slider arm connected to Terminal 4. Cascode connected bipolar

transistors Q2, Q5 are the constant current source for the input stage. The base biasing

circuit for the constant current source is described subsequently. The small diodes D3,

D4, D5 provide gate oxide protection against high voltage transients, e.g., static

electricity.

Second Stage:

Most of the voltage gain in the CA3140 is provided by the second amplifier

stage, consisting of bipolar transistor Q13 and its cascode connected load resistance

provided by bipolar transistors Q3, Q4. On-chip phase compensation, sufficient for a

majority of the applications is provided by C1. Additional Miller-Effect compensation

(roll off) can be accomplished, when desired, by simply connecting a small capacitor

between Terminals 1 and 8. Terminal 8 is also used to strobe the output stage into

quiescence. When terminal 8 is tied to the negative supply rail (Terminal 4) by

mechanical or electrical means, the output Terminal 6 swings low, i.e., approximately

to Terminal 4 potential.

Output Stage:

The CA3140 Series circuits employ a output stage that can sink loads to the

negative supply to complement the capability of the PMOS input stage when

operating near the negative rail. Quiescent current in the emitter-follower cascade

circuit (Q17, Q18) is established by transistors (Q14, Q15) whose base currents are


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“mirrored” to current flowing through diode D2 in the bias circuit section. When the

CA3140 is operating such that output Terminal 6 is sourcing current, transistor Q18

functions as an emitter-follower to source current from the V+ bus (Terminal 7), via

D7, R9, and R11. Under these conditions, the collector potential of Q13 is sufficiently

high to permit the necessary flow of base current to emitter follower Q17 which, in

turn, drives Q18. When the CA3140 is operating such that output Terminal 6 is sinking

current to the V- bus, transistor Q16 is the current sinking element. Transistor Q16 is

mirror connected to D6, R7, with current fed by way of Q21, R12, and Q20. Transistor

Q20, in turn, is biased by current flow through R13, zener D8, and R14.

Dynamic Current Sink:

The dynamic current sink is controlled by voltage level sensing. For purposes

of explanation, it is assumed that output Terminal 6 is quiescently established at the

potential midpoint between the V+ and V- supply rails. When output current sinking

mode operation is required, the collector potential of transistor Q13 is driven below its

quiescent level, thereby causing Q17, Q18 to decrease the output voltage at Terminal 6.

Thus, the gate terminal of PMOS transistor Q21 is displaced toward the V- bus,

thereby reducing the channel resistance of Q21. As a consequence, there is an

incremental increase in current flow through Q20, R12, Q21, D6, R7, and the base of Q16.

As a result, Q16 sinks current from Terminal 6 in direct response to the incremental

change in output voltage caused by Q18. This sink current flows regardless of load;

any excess current is internally supplied by the emitter-follower Q18.

Applications:

Sample and Hold Amplifiers.

Long Duration Timers/Multivibrators

Photocurrent Instrumentation

Active Filters, Comparators and Function Generators.


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Interface in 5V TTL systems and low supply voltage systems.

All Slandered Operational Amplifier Applications.

2.3 A DETAIL STUDY OF IC LM3915

The LM3915 is a dot/bar display driver. It is a monolithic integrated circuit

that senses analog voltage levels and drives ten LEDs, LCDs or vacuum fluorescent

displays, providing a logarithmic 3dB/step analog display. One pin changes the

display from a bar graph to a moving dot display. LED current drive is regulated and

programmable, eliminating the need for current limiting resistors. The whole display

system can operate from a single supply as low as 3V or as high as 25V.

The IC contains an adjustable voltage reference and an accurate ten-step

voltage divider. The high-impedance input buffer accepts signals down to ground and

up to within 1.5V of the positive supply. Further, it needs no protection against inputs

of ±35V. The input buffer drives 10 individual comparators referenced to the

precision divider. Accuracy is typically better than 1 dB.

The LM3915’s 3 dB/step display is suited for signals with wide dynamic

range, such as audio level, power, light intensity or vibration. Audio applications

include average or peak level indicators, power meters and RF signal strength meters.

Replacing conventional meters with an LED bar graph results in a faster responding,

more rugged display with high visibility that retains the ease of interpretation of an

analog display.

The LM3915 is extremely easy to apply. A 1.2V full-scale meter requires only

one resistor in addition to the ten LEDs. One more resistor programs the full-scale

anywhere from 1.2V to 12V independent of supply voltage. LED brightness is easily

controlled with a single pot. The LM3915 is very versatile. The outputs can drive

LCDs, vacuum fluorescents and incandescent bulbs as well as LEDs of any color.

Multiple devices can be cascaded for a dot or bar mode display with a range of 60 or

90 dB. LM3915s can also be cascaded with LM3914s for a linear/ log display or with

LM3916s for an extended-range VU meter.


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Pin Out:

The IC LM3915 is available in an 18-lead molded DIP package, which

drives 10 LED’s from pin-10 to pin-18 and pin-1. The Dot or Bar display mode can

be selected externally by the user.


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Figure 2.2.1: Pin out of IC LM3915

Pin No Name Purpose

1 Led No 1 This pin is used for the connection of LED

2 V- The supply voltage which must between 3V and

25V.3 V+

4Divider(Low

End)

Pin-4 and Pin-6 is used for the 10 step voltage

divider circuit. That provides differential input

voltage which must be applied to each comparator to

bias the output in the linear region.6

Divider(High

End)

5 Signal Input Pin-5 acts as the input pin.

7 Reference Output The reference is designed to be adjustable and

develops a nominal 1.25V between the REF OUT

(pin 7) and REF ADJ (pin 8) terminals. 8 Reference Adjust

9 Mode Select

This pin is used for the selecting the mode of the IC.

If it is connected to V+ it gives the Bar graph display,

if it is open circuited then it gives Dot graph display.

10 - 18 Led No 2 to 10 This pins are used for the connection of LED’s

Table 3: LM3915 pin name and their purpose

Block Diagram:


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The block diagram of IC LM3915 is show below.

Figure 2.2.2: Block Diagram of IC LM3915

Description:

The simplified LM3915 block diagram is included to give the general idea of

the circuit’s operation. A high input impedance buffer operates with signals from

ground to 12V, and is protected against reverse and overvoltage signals. The signal is

then applied to a series of 10 comparators; each of which is biased to a different

comparison level by the resistor string.

In the example illustrated, the resistor string is connected to the internal 1.25V

reference voltage. In this case, for each 3 dB that the input signal increases, a

comparator will switch on another indicating LED. This resistor divider can be


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connected between any 2 voltages, providing that they are at least 1.5V below V+ and

no lower than V−.

Internal Voltage Reference:

The reference is designed to be adjustable and develops a nominal 1.25V

between the REF OUT (pin 7) and REF ADJ (pin 8) terminals. The reference voltage

is impressed across program resistor R1 and, since the voltage is constant, a constant

current I1 then flows through the output set resistor R2 giving an output voltage of:

VOUT = VREF (1+(R2/R1))+IADJR2

Since the 120 μA current (max) from the adjacent terminal represents an error term,

the reference was designed to minimize changes of this current with V+ and load

changes. For correct operation, reference load current should be between 80 μA and 5

mA. Load capacitance should be less than 0.05 μF.

Specifications:

The specifications of IC LM3915 are given below...

Power Dissipation - 1365 mW

Supply Voltage - 25V

Input Signal Overvoltage - ±35V

Divider Voltage - -100 mV to V+

Storage Temperature Range - -55oC to +150oC


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Parameter Condition Typical Value Units

Comparator

Offset Voltage0V ≤ VRLO = VRHI ≤ 12V, ILED = 1

mA3 mV

Gain (ΔILED/ΔVIN) IL(REF) = 2 mA, ILED = 10 mA 8 mA/mV

Input Bias Current 0V ≤ VIN ≤ (V+ − 1.5V) 25 nA

Voltage –Divider

Divider Resistance Total, Pin 6 to 4 28 kΩ

Relative Accuracy - 3 dB

Voltage Reference

Output Voltage0.1 mA ≤ IL(REF) ≤ 4 mA, V+ =

VLED = 5V1.28 V

Line Regulation 3V ≤ V+ ≤ 18V 0.01 %/V

Load Regulation0.1 mA ≤ IL(REF) ≤ 4 mA, V+ =

VLED = 5V0.4 %

Output Voltage with

change in

Temperature

0°C ≤ TA ≤ +70°C, IL(REF) = 1 mA,

V + = VLED = 5V1 %

Output Drivers

LED Current V + = VLED = 5V, IL(REF) = 1 mA 10 mA

LED Current

Difference

VLED = 5V, ILED = 2 mA

VLED = 5V, ILED = 20 mA

0.12mA

1.2

LED Current

Regulation

2V ≤ VLED ≤ 17V, ILED = 2 mA

2V ≤ VLED ≤ 17V, ILED = 20 mA

0.1mA

1

Dropout VoltageILED(ON) = 20 mA, VLED = 5V, ΔILED = 2

mA1.5 V

Saturation Voltage ILED = 2.0 mA, IL(REF) = 0.4 mA 0.15 V

Output LeakageBar Mode 0.1

µADot Mode 0.1

Table 4: Specifications of IC LM3915


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Definition of Terms:

Absolute Accuracy: The difference between the observed threshold voltage and the

ideal threshold voltage for each comparator. Specified and tested with 10V across the

internal voltage divider so that resistor ratio matching error predominates over

comparator offset voltage.

Adjust Pin Current: Current flowing out of the reference adjust pin when the

reference amplifier is in the linear region.

Comparator Gain: The ratio of the change in output current (ILED) to the change in

input voltage (VIN) required to produce it for a comparator in the linear region.

Dropout Voltage: The voltage measured at the current source outputs required to

make the output current fall by10%.

Input Bias Current: Current flowing out of the signal input when the input buffer is

in the linear region.

LED Current Regulation: The change in output current over the specified range of

LED supply voltage (VLED) as measured at the current source outputs. As the

forward voltage of an LED does not change significantly with a small change in

forward current, this is equivalent to changing the voltage at the LED anodes by the

same amount.

Line Regulation: The average change in reference output voltage (VREF) over the

specified range of supply voltage (V+).

Load Regulation: The change in reference output voltage over the specified range of

load current (IL (REF)).

Offset Voltage: The differential input voltage which must be applied to each

comparator to bias the output in the linear region. Most significant error when the

voltage across the internal voltage divider is small. Specified and tested with pin 6

voltage (VRHI) equal to pin 4 voltages (VRLO).


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Relative Accuracy: The difference between any two adjacent threshold points.

Specified and tested with 10V across the internal voltage divider so that resistor ratio

matching error predominates over comparator offset voltage.

Typical Connection:

The typical connection of IC LM3915 is as shown below.

Figure 2.2.3: Typical Connection of IC LM3915

The reference voltage and the current through LED’s is given as

VREF = 1.25V (1+R2/R1) +R2+80µA

ILED = 12.5V/R1) + (VREF/2.2KΩ)

The above circuit is wired in DOT mode. For BAR mode, connect the pin-3 to

pin-9. The LED supply should be bypassed with a 2.2µF Tantalum of 10µF aluminum

electrolytic capacitor to avoid the oscillations from the load resistance.

Features

3 dB/step, 30 dB range

Drives LEDs, LCDs, or vacuum fluorescents

Bar or dot display mode externally selectable by user

Expandable to displays of 90 dB


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Internal voltage reference from 1.2V to 12V

Operates with single supply of 3V to 25V

Inputs operate down to ground

Output current programmable from 1 mA to 30 mA

Input withstands ±35V without damage or false outputs

Outputs are current regulated, open collectors

Directly drives TTL or CMOS

The internal 10-step divider is floating and can be referenced to a wide range

of voltages

The LM3915 is rated for operation from 0˚C to +70˚C.


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2.4 BC557 AND ITS CHARACTERISTICS

Description:

BC557 is a PNP general purpose transistor. The three pins of the transistor are

namely Emitter (E), Base (B), and Collector (C). The PNP transistor in general

requires the low input in order to operate it as a closed switch.

Identification of Pins:

To identify the pins, keep the transistor so that notch is facing you and from the left

first pin is emitter, second pin is base and third pin is collector.

Pin diageram of BC557 is shown in figure6.

Figure 2.3.1:Pin diagram of BC557 transistor

Features:

•Low current (max. 100 mA)

•Low voltage (max. 65 V).

Limiting Values:

Collector – Base Voltage (VCBO) = -50V

Collector – Emitter Voltage(VCEO) = -45V

Emitter – Base Voltage(VBEO) = -5V

Collector Current (IC) = -100mA


AQUARIUM PROBE

Characteristics:

The characteristics of the BC557 transistor are mentioned in the following

table.

SYMBOL PARAMETER CONDITIONS MIN MAX UNIT

ICBO collector-base cut-off

current

VCB = −30 V; IE =0 A − -15 nA

VCB = −30 V; IE = 0 A;

Tj= 150 °C

− -4 µA

IEBO emitter-base cut-off

current

VEB = −5 V; IC =0 V − -100 nA

hFE DC current gain IC = −2 mA; VCE = −5V 125 800

VCEsat collector-emitter

saturation

voltage

IC = −10 mA; IB = −0.5 mA − -300 mV

IC = −100 mA; IB = −5mA − -650 mV

VBEsat base-emitter saturation

voltage

IC = −10 mA; IB = −0.5 mA − − mV

IC = −100 mA; IB = −5 mA − − mV

VBE base-emitter voltage VCE = −5 V; IC = −2 mA -600 -750 mV

VCE = −5 V; IC = −10 mA − -820 mV

Cc collector capacitance VCB = −10 V; IE =ie = 0 A;

f = 1 MHz

− pF

Ce emitter capacitance VEB = −0.5 V; IC =ic = 0 A;

f = 1 MHz

− − pF

fT transition frequency VCE = −5 V; IC = −10 mA;

f = 100 MHz

100 − MHz

F noise figure VCE = −5 V; IC = −200 µA;

RS =2kΩ;

f = 1 kHz; B = 200 Hz

− 10 dB

Table 5: Characteristics of BC 557

Applications

•General purpose switching and amplification


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2.5 VOLTAGE REGULATORS

Definition:

The Voltage regulators are used to produce fixed DC output voltage. Let think

that you are producing a dc voltage from the ac supply using a rectifier and the output

of the rectifier is driving a circuit; the rectifier output may not be unchanging which

may result an imperfect output of the driven circuit. Hence it’s a need to maintain a

fixed voltage to produce a balanced output and so we require the VRs.

Voltage Regulators, also known as voltage stabilizers, are semiconductor

devices that output a constant and stable DC voltage at a specified level, despite

fluctuations in its input voltage or variations in its load. Voltage regulator IC's have

already become available in so many forms and characteristics that they've virtually

eliminated the need to build voltage regulating circuits from discrete components.

Factors that spurred the growth of the voltage regulator IC business include: 1)

ease with which zener diodes and balanced amplifiers can be built into IC's; 2)

improved IC heat dissipation capabilities; 3) advances in overload protection

techniques; and of course, 4) a high demand for voltage regulators in almost all fields

of the electronics industry, especially in power supply applications.

Description:

Generally we get fixed output voltage by connecting voltage regulator at the output of

filtered DC. It is used in the circuits to get low DC voltage from high DC voltage. In

usual we have two major classes of the VRs and they are mentioned below.

TYPES OF VOLTAGE REGULATORS:

There are several types of voltage regulators, which may be classified in terms of

how they operate or what type of regulation they offer.

The types of VRs that are classified depending on the output voltage are as

follows

1. Fixed voltage regulators

2. Variable voltage regulators


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1. FIXED VOLTAGE REGULATORS:

The Fixed voltage regulators are those which produce fixed or constant output

DC voltage. The resistances used in these types of voltage regulators are fixed and

cannot be varied hence these VRs produce constant output voltage.

2. VARIABLE VOLTAGE REGULATORS:

The Variable voltage regulators are those which produce the variable voltage

at the output, it means that the outputs of these VRs can be varied using the variable

resistance.

These VRs are again classified into two, depending on the output voltage

obtained as positive or negative. They are mentioned as follows:

1. Positive voltage regulators

2. Negative voltage regulators

1. POSITIVE VOLTAGE REGULATOR: If the output of voltage regulator is

positive then it is called positive voltage regulator. These include 78xx voltage

regulators. The most commonly used ones are 7805 and 7812.

2. NEGATIVE VOLTAGE REGULATOR: If the output of voltage regulator is

negative voltage then it is called negative voltage regulator. Mostly available negative

voltage regulators are of 79xx family.

The picture of voltage regulator is shown in figure7

Figure 2.4.1:Picture of voltage regulator

PIN1-INPUT PIN2-GROUND PIN3-OUTPUT


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The series 7800 regulators provide eight voltage options, ranging from 5 to 24

V. These ICs are designed as fixed voltage regulators and with adequate heat sinking

can deliver output currents in excess of 1 A. Although these devices do not require

any external component, such components can be employed for providing adjustable

voltages and currents. These ICs also have internal thermal overload protection and

internal short-circuit current limiting.

Figure illustrates how one such IC, a 7815, is connected to provide voltage

regulation with output of + 15 V dc from this unit. An unregulated, input voltage Vin

is filtered by capacitor C, and connected to the pin .1 (IN terminal) of IC. The pin 2

(OUT terminal) of the IC provides a regulated + 15 V which is filtered by capacitor

C2 (mostly for any high frequency noise). The third pin (GND terminal) of the IC is

connected to ground. While the input voltage may vary over some permissible voltage

range, and the output load may vary over some acceptable range, the output voltage

remains constant within specified voltage variation limits. These limitations are

mentioned in the manufacturer’s specification sheet.

In addition, the difference between input and output voltages (Vin- Vout),

callec the dropout voltage, must be typically 20 V, even during the low point on the

input ripple voltage. Furthermore, the capacitor C1, is required if the regulator is

located an appreciable distance from a power supply filter. Even though C2 is not

required, it may be used to improve the transient response of the regulator.

Figure 2.4.2: Block


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Absolute Maximum Ratings:

The absolute maximum values for the 78XX series VRs are mentioned in the

following table:

SYMBOLPARAMETER VALUE UNIT

Vi DC InputVoltage (for VO = 5 to 18V)

(forVO = 20, 24V)

35

40

V

V

Io OutputCurrent Internally limited

Ptot Power Dissipation Internally limited

Top Operating Junction Temperature Range (for

L7800)

(for L7800C)

-55 to 150

0to150

Oc

oC

Tstg Storage Temperature Range -65 to 150 oC

Table 6: Absolute Maximum Ratings of VR 78XX series

IC3-7805(Voltage regulator) :

1. 7805 is a fixed voltage regulator.

2. 7805 voltage regulator gives fixed voltage of 5V DC voltage, if the input

voltage is around 7.5V to 20V.

3. It can take a higher, crappy DC voltage and turn it into a nice, smooth 5 volts

DC.

4. You need to feed it at least 8 volts and no more than 30 volts to do this.

5. It can handle around .5 to .75 amps, but it gets hot. Use a heatsink.

6. Use it to power circuits than need to use or run off of 5 volts.

7. If it is <7.5V regulation wont be proper.

8. Heat sink is used on the top of IC to avoid damage of IC.

9. In the circuit, 7805 provides regulated 5 volts to the inputs of IC1, so that the

input voltage is stable for accurate measurement.

Pin diagram of 7805 is shown in figure 2.4.3.


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Figure 2.4.3:Pin diagram of Voltage regulator 7805

IC4-7809(Voltage regulator) :

1. 7809 is a fixed voltage regulator.

2. It gives fixed voltage of 9V DC voltage.

3. In the circuit, 7809 provides regulated 9V DC to the circuit.

4. It can take a higher, crappy DC voltage and turn it into a nice, smooth 9 volts

DC.

5. Heat sink is used on the top of IC to avoid damage of IC.

Pin diagram of 7809 is shown in figure 2.4.4

Figure 2.4.4:Pin diagram of Voltage regulator 7809


7805

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2.6 A BRIEF STUDY OF DIODE 1N34

Description:

The germanium point contact diodes are widely used for detecting the rectifying

efficiency or for switching on the radio, TV, or studio, etc. 1N34 is a sensor diode

which is used to sense the required temperature.

Picture of diode 1N34 is shown in figure10.

Figure2.5.1: Picture of diode 1N34

Maximum Rating:

· Operating temperature: -65OC to +75OC

· Storage temperature: -65OC to +75OC

parameter symbol value Unit

Peak reverse voltage VRM 45 V

Reverse voltage DC VR 20 V

Peak forward current IFM 150 mA

Average rectified

output current

IO 50 mA

Surge forward current Isurge 700 mA

Junction temperature Tj 75 0C

Storage temperature

range

TS -55 TO +75 0C

Table 7: Characteristics of BC557


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Features:

Low leakage current

Flat junction capacitance

High mechanical strength


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2.7 BRIDGE RECTIFIER AND ITS WORKING

The rectifiers are generally used to convert the ac voltage into the dc voltage.

It may sometimes require for user to provide continuous dc to the circuit, if we use a

battery it may not provide the continuous dc, they may lose the charge after the use

for a long time. Hence we require rectifiers to provide constant dc, which is

converted from ac voltage.

The Full Wave Bridge Rectifier

Another type of circuit that produces the same output waveform as the full

wave rectifier circuit above is that of the Full Wave Bridge Rectifier. This type of

single phase rectifier uses four individual rectifying diodes connected in a closed loop

"bridge" configuration to produce the desired output. The main advantage of this

bridge circuit is that it does not require a special centre tapped transformer, thereby

reducing its size and cost. The single secondary winding is connected to one side of

the diode bridge network and the load to the other side as shown below.

The Diode Bridge Rectifier

Fig 2.6.1: Diode Bridge Rectifier

The four diodes labelled D1 to D4 are arranged in "series pairs" with only two diodes

conducting current during each half cycle. During the positive half cycle of the

supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse

biased and the current flows through the load as shown below.


AQUARIUM PROBE

The Positive Half-cycle

During the negative half cycle of the supply, diodes D3 and D4 conduct in

series, but diodes D1 and D2 switch of as they are now reverse biased. The current

flowing through the load is the same direction as before.

The Negative Half-cycle

As the current flowing through the load is unidirectional, so the voltage

developed across the load is also unidirectional the same as for the previous two diode

full-wave rectifier, therefore the average DC voltage across the load is 0.637Vmax and

the ripple frequency is now twice the supply frequency (e.g. 100Hz for a 50Hz

supply).

Typical Bridge Rectifier

Although we can use four individual power diodes to make a full wave bridge

rectifier, pre-made bridge rectifier components are available "off-the-shelf" in a range

of different voltage and current sizes that can be soldered directly into a PCB circuit

board or be connected by spade connectors. The image to the right shows a typical

single phase bridge rectifier with one corner cut off. This cut-off corner indicates that

the terminal nearest to the corner is the positive or +ve output terminal or lead with

the opposite (diagonal) lead being the negative or -ve output lead. The other two

connecting leads are for the input alternating voltage from a transformer secondary

winding.

The Smoothing Capacitor

We saw in the previous section that the single phase half-wave rectifier

produces an output wave every half cycle and that it was not practical to use this type

of circuit to produce a steady DC supply. The full-wave bridge rectifier however,

gives us a greater mean DC value (0.637 Vmax) with less superimposed ripple while

the output waveform is twice that of the frequency of the input supply frequency. We

can therefore increase its average DC output level even higher by connecting a

suitable smoothing capacitor across the output of the bridge circuit as shown below.

Full-wave Rectifier with Smoothing Capacitor

The smoothing capacitor converts the full-wave rippled output of the rectifier

into a smooth DC output voltage. Generally for DC power supply circuits the

smoothing capacitor is an Aluminum Electrolytic type that has a capacitance value of


AQUARIUM PROBE

100uF or more with repeated DC voltage pulses from the rectifier charging up the

capacitor to peak voltage.

Fig 2.6.2: Bridge Rectifier with capacitor

Fig 2.6.3: Waveforms obtained for the Bridge Rectifier

However, there are two important parameters to consider when choosing a

suitable smoothing capacitor and these are its Working Voltage, which must be higher

than the no-load output value of the rectifier and its Capacitance Value, which

determines the amount of ripple that will appear superimposed on top of the DC

voltage. Too low a value and the capacitor has little effect but if the smoothing

capacitor is large enough (parallel capacitors can be used) and the load current is not


T

Time (s)

0.00 20.00m 40.00m 60.00m

Vo

lta

ge

(V

)

-10.00

-5.00

0.00

5.00

10.00

AQUARIUM PROBE

too large, the output voltage will be almost as smooth as pure DC. As a general rule of

thumb, we are looking to have a ripple voltage of less than 100mV peak to peak.

The maximum ripple voltage present for a Full Wave Rectifier circuit is not only

determined by the value of the smoothing capacitor but by the frequency and load

current, and is calculated as:

Bridge Rectifier Ripple Voltage

VRIPPLE = ILOAD/fc volts

Where: I is the DC load current in amps, ƒ is the frequency of the ripple or twice the

input frequency in Hertz, and C is the capacitance in Farads.

The main advantages of a full-wave bridge rectifier is that it has a smaller AC ripple

value for a given load and a smaller reservoir or smoothing capacitor than an

equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple

voltage is twice that of the AC supply frequency (100Hz) where for the half-wave

rectifier it is exactly equal to the supply frequency (50Hz).


AQUARIUM PROBE

Chapter – 3

CIRCUIT OPERATION

The Aquarium Probe circuit is depicted in the following figure. The figure

majorly consists of two main stages; the first one is the IC CA3140 Op-Amp acts as

inverting amplifier and the latter is the IC LM3915 helps in driving the outputs. The

major elements which play an important role in the operation of the circuit are

explained individually in the following lines.

1N34 – Germanium diode:

The germanium diode 1N34 in this circuit acts as the temperature sensing

probe. It means that this diode acts as a temperature to voltage converter. The

resistance of the diode depends on the temperature in its vicinity. In general, the

diode generate around 600mV, when a potential difference is applied across its

terminals. And it generates 2mV output voltage for each degree of centigrade rise in

the temperature.

IC CA3140 – Inverting Amplifier:

The CA3140 (IC1) is the CMOS version op-amp that can operate down to

zero-volt output. The input to the CA3140 is taken from the diode 1N34. The VR

7805 provides the supply voltage 5V to the IC. The advantage of CA3140 is, for

every small change in the input its shows the response in the output.

IC LM3915 – Display driver:

The display driver LM3915 helps in driving the outputs. This means the

outputs of the Display Driver depends on the inputs that had taken. It generally can

be operated in two modes, one is Dot and other is Bar mode. Here in this circuit, IC

LM3915 works in a Dot mode and drives two LEDs and a Piezo Buzzer.

VR 7805 and VR 7809:

The Voltage Regulators 7805 and 7809 helps in providing the constant supply

voltages. The VR 7805 provides a constant voltage of 5V to the IC CA3140, so that

the input voltage is stable for accurate measurement of temperature. The other VR

7809 helps in providing the constant voltage of 9V to the whole circuit.


AQUARIUM PROBE

BC 557 – PNP Transistor:

The PNP transistor, BC 557 in this circuit helps in driving the Piezo Buzzer.

It acts as a switch, and as it is a PNP transistor it requires low input to operate it in a

closed switch mode. The IC LM3915 drives the transistor, it means when the 16 pin

of IC becomes low, the transistor conducts and hence it activates the Piezo Buzzer.

Variable Resistors:

The four variable resistors that are in the circuit are used for different purposes

and they are mentioned below.

VR1 – 1KΩ: this is at the input of the IC CA3140 and it sets the input voltage

at the pin 3 of IC CA3140.

VR2 – 1MΩ: this is at the output side of the IC CA3140 and the VR2

amplifies the input to the required level.

VR3 – 50KΩ: the VR3 is used to provide the required level of voltage to the

IC LM3915.

VR4 – 4.7KΩ: the VR4 is connected to 7th pin of IC LM3915 and is grounded

and helps in maintaining the sensitivity of the IC LM3915.

The following are the resistors play a major role in the circuit and are explained

individually:

R1 – 47KΩ: this resistor restricts the current flow through diode 1N34.

R4 – 100KΩ: this resistor along with the VR2 helps IC CA3140 in

amplification process.

R7 – 1KΩ: it is connected to the base of the transistor BC 557 and helps in

avoiding the false alarm.

LEDs and Piezo Buzzer:

The circuit has two LEDs, one is green and the other is red. Each of them will

indicate different temperature ranges, the green indicates the normal temperatures and

the red indicates the critical temperatures. The Piezo buzzer will be activated and

sounds when the temperature enters into very critical values.

Circuit Operation:


AQUARIUM PROBE

The operation of Aquarium Probe is quite simple; the diode 1N34 is generally

kept inside a glass tube and is immersed in water. The diode senses the temperature

and the resistance of the diode will be varied according to the temperature it sensed.

Usually the diode output voltage increase 2mV for each degree of Centigrade rise in

temperature.

The diode’s one terminal is connected to the 2nd pin of IC CA3140, which acts

as an inverting amplifier. In general, the IC CA3140 provides a maximum of 2.25V.

The feedback VR2 helps in amplifying the input to the required amount voltage. The

amplified voltage from IC CA3140 is then passed to the display driver through the

VR3. The VR3 helps in varying the voltage that is provided to the IC LM3915. The

LM3915 acts as a display driver in Dot mode and drives the LEDs and a Piezo

Buzzer.

Depending on the input received, the IC LM3915 drives the two LEDs and it

also drives piezo buzzer through the transistor BC557. The transistor acts as a switch

and the piezo buzzer will become active when the switch is closed that means when

the transistor conducts. As the transistor is PNP type, it requires the low voltage at

the input side for conduction. There will be a resistor R7, which helps in avoiding the

false alarm.

Let us discuss the operation in practical, assume the water is at some 200C,

and then the diode 1N34 which is immersed in the water generates an output voltage

of 40mV. As the diode increases the output voltage by 2mV for each degree of

centigrade rise in temperature, the output will be 60mV if the water is at the

temperature of 300C. With each step increase of 30 mV in the input (corresponding to

15°C rise in temperature), LEDs and the buzzer become active.

The display driver drives the LEDs and Piezo buzzer on following the three

important conditions. They are given below:

If the voltage is reached to the crossing point 70mV, it means that the

temperature is approximately at 350C. At this point the GREEN LED will

glow indicating that the water temperature is reached to 350C.


AQUARIUM PROBE

If the voltage is increased to certain level crossing the 70mV and reached to

100mV, then it means that the water temperature is increased. The RED LED

will glows and indicates that the temperature is reached to 500C.

If the voltage is further increased more to 130mv, then the IC LM3915 drives

the transistor BC 557, and the transistor conducts, which makes the piezo

buzzer to become active and hence the buzzer beeps indicating that the

temperature of water entered into very critical region of 650C.

The sensitivity of IC LM3915 and the gain of the inverting amplifier can be

varied by using the Variable Resistors and the voltage regulators in helps in providing

the constant supply voltage.


AQUARIUM PROBE

Chapter - 4

APPLICATIONS

The Aquarium Probe has many practical applications. As the fish cannot

survive in the hot temperature waters, we need to keep an eye on the temperature of

water in aquarium.

As the today’s world became machinery one cannot checks the Aquarium

regularly. So the Aquarium probe will be very much helpful in indicating the

temperature of water in the following conditions.

APPLICATIONS:

It is used in the places where people forget to change the aquarium water.

These are used in hotels and restaurants where the workers are busy and

forget to change aquarium water.

Most of the busy workers use this device in homes so that they can change

water when ever buzzer makes sound.

Figure 4.1: Practical application of Aquarium Probe


Temperature sensing device diode 1N34

Piezo Buzzer

Red LED

GreenLED

AC supply

AQUARIUM PROBE

The above depicted figure is the practical usage of the Aquarium Probe. The

glass tube consisting of diode is to be attached to the aquarium such that the glass tube

is immersed in the water.

ADVANTAGES:

The use of small compact elements and IC’s makes the circuit simple and less

complex.

The circuit is easy to understand because of presence of basic elements.

The circuit is portable, hence it can be carried anywhere.

The circuit consumes less power due to presence of 9V battery.

The result can be easily understandable due to presence of LED’s and piezo

buzzer.

The life of the circuit is more because the IC’s used are not easily breakable

and damaged.

The diode used in the circuit is more sensitive from low temperature to high

temperature. Hence the response of the diode due to small variations in the

temperature is very faster.

The use of voltage regulators reduces the breakage of IC’s from AC voltage

and other components and allows the required voltage to be passed to the

components.

It makes to identify the present temperature of water very easily than the use

of thermometer every time.

The device cost is less and easy to handle.

DISADVANTAGES:

The circuit is not water resistant. Hence it should be kept outside the water

except the probe that contains the diode.

The circuit is just used for indication but it cannot handle the temperature by

increasing or decreasing the temperature.

Since we cannot get the low voltage directly, the use of bridge rectifier and

adaptor makes the circuit somewhat complex.


AQUARIUM PROBE

Precautions:

Though the circuit is very simple and easy to operate we have to take some

safety measures in order to obtain the exact results. The diode 1N34 is the

temperature sensor and plays a major role at the input side and it is to be immersed in

the water to sense the temperature. Here one must note that the diode 1N34 should

not be immersed directly into the water, because it may lead to shorting.

Hence to avoid this problem the terminals of the diode 1N34 should be coated

with enamel paint and should be kept inside a glass tube to make it water proof. The

care should be taken in adjusting and setting the circuit.

One other important thing is the usage of LEDs. They should not be directly

supplied with the DC voltage. If the voltage is directly supplied to LEDs, they will be

damaged; hence the resistance must be added in between the supply voltage and the

LED.


AQUARIUM PROBE

Chapter – 5

RESULT OF THE DESIGN

The circuit was professionally designed with less complexity without any

drawbacks. The following is the result what we obtained during our experiment -

When approximately 70 mV is provided to the input of IC2 by adjusting preset

VR3, LED1 (green) lights up to indicate that the temperature is approximately

35°C, which is the crossing point. When the input receives 100mV, LED2

(red) lights up to indicate approximately 50°C.

Finally, the buzzer starts beeping if the input receives 130 mV corresponding

to a temperature of 65°C. In short, LEDs and the buzzer remain standby when

the temperature of the water is below 35°C (normal). With each step increase

of 30 mV in the input (corresponding to 15°Crise in temperature), LEDs and

the buzzer become active.

The Aquarium Probe circuit designed indicates the temperature accurately but it

doesn’t measures the temperature. It provides greater accuracy; a small change in

temperature will be indicated at the output. Besides some precautions to be taken, the

Aquarium Probe works nicely.

Future:

At present we are using LEDs to indicate the temperature. The LEDs are used just

for identification of present temperature so that we can assume that the temperature is

between 30-50 degree centigrade.

In future we can use digital display or an LCD screen instead of LED’s to display

the exact temperature and to know their values at what temperature they are present.

So that it makes easy to identify the exact temperature and also a small variation in

the temperature can be seen easily.

At present we are just identifying the temperature of water, but we cannot change

the temperature of water. If we are in busy or not present close to aquarium, due to

increase of temperature the fishes may die. To overcome this, in future, we can use


AQUARIUM PROBE

coolants which will decrease the temperature without our presence. The process will

be carried out automatically according to the variations in the temperature of water.

Chapter – 6

CONCLUSION

The Aquarium probe circuit described here is a latest technology which can

indicate the temperature automatically. Even though there are many commercial

products available in the market for indication of environmental parameters, the

Aquarium Probe circuit mentioned here is the simple. But the only drawback with

this is it cannot be able to measure the temperature, we can only approximate

temperature,

As the technology advanced many new devices like cooling probe and others

entered the market, the Aquarium Probe still exists in the market due to its low cost.

The present commercial products that are in the market can measure the almost all

environmental parameters like pH and others, but they are very tough to maintain.

However the Aquarium Probe circuit mentioned here automatically indicates the

temperature of aquarium water and it costs low. And the design of the circuit is

meant for the portable nature, that can be carried anywhere and can be handled easily

and of low cost.


AQUARIUM PROBE

COST DETAILS:


S.NO NAME OF COMPONENT VALUE PRICE

1. OP-AMP, IC1 CA3140 Rs.12

2. DISPLAY DRIVER, IC2 LM3915 Rs.30

3. VOLTAGE REGULATORS, IC3

IC4

7805

7809

Rs.5

Rs.5

4. DIODE, D1 1N34 Rs.4

5. TRANSISTOR, T1 BC557 Rs.2

6. CAPACITOR, C1 1μF, 25V Rs.2

7. RESISTORS, R1

R2

R3

R4

R5,R6,R7

47KΩ

47KΩ

470Ω

100Ω

1KΩ, 1KΩ, 1KΩ

Rs.1

Rs.1

Rs.0.5

Rs.0.5

Rs.1.5

8. VARIABLE RESISTORS, VR1

VR2

VR3

VR4

1KΩ

1MΩ

50KΩ

4.7KΩ

Rs.0.5

Rs.1

Rs.1

Rs.0.5

9. LEDs, RED & GREEN Rs.2

10. PIEZO BUZZER, PZ1 Rs.15

11. BATTERY 9V Rs.20

AQUARIUM PROBE

REFERENCES:

[1]. Integrated Electronics by Jacob Millman, TATA Mc Graw hill edition

[2]. www.electroniceforu.com.

[3]. www.electrokits.com.

[4]. www.national.com & www.datasheetcatalog.com.

[5]. www.intersil.com

[6]. http://www.siliconfareast.com/voltage-regulators.htm

[7]. http://www.ehow.com/about_4964098_types-voltage-regulators.html

[8].http://www.globalspec.com/Specifications/Semiconductors/

Power_Management_Chips/IC_Voltage_Regulators

[9]. www.datasheetcatalog.com & www.datasheetsite.com.

[10]. http://www.icknowledge.com/history/history.html


http://www.icknowledge.com/history/history.html

http://www.datasheetsite.com/

http://www.datasheetcatalog.com/

http://www.globalspec.com/Specifications/Semiconductors/Power_Management_Chips/IC_Voltage_Regulators

http://www.globalspec.com/Specifications/Semiconductors/Power_Management_Chips/IC_Voltage_Regulators

http://www.ehow.com/about_4964098_types-voltage-regulators.html

http://www.siliconfareast.com/voltage-regulators.htm

http://www.intersil.com/

http://www.datasheetcatalog.com/

http://www.national.com/

http://www.electrokits.com/

http://www.electroniceforu.com/

AQUARIUM PROBE

PHOTO COPIES


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INDEX

Absolute accuracy 24

Comparator gain 24

Display driver 8

Drop out voltage 24

Dynamic current sink 18

IC CA3140 12

Pin out 13

IC LM3915 19

Pin out 19

Input bias current 24

Integrated Circuit 10

Offset voltage 24

Rectifier 36

Relative accuracy 25

Ripple Voltage 39

Smoothing capacitor 37

Typical Bridge Rectifier 37

Variable Resistors 41

Voltage Regulator 27

7805 32

7809 33


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