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
GPCET 2 Department Of ECE
AQUARIUM PROBE
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
GPCET 3 Department Of ECE
AQUARIUM PROBE
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
GPCET 4 Department Of ECE
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.
GPCET 5 Department Of ECE
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.
GPCET 6 Department Of ECE
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
GPCET 7 Department Of ECE
INVERTING AMPLIFIER IC CA3140
INPUT STAGEDIODE 1N34
DISPLAY DRIVER IC LM3915
OUTPUT STAGE
GREEN ANDRED LEDS
PIEZO BUZZER
AQUARIUM PROBE
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.
GPCET 8 Department Of ECE
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.
GPCET 9 Department Of ECE
AQUARIUM PROBE
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.
GPCET 10 Department Of ECE
AQUARIUM PROBE
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.
GPCET 11 Department Of ECE
AQUARIUM PROBE
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
GPCET 12 Department Of ECE
AQUARIUM PROBE
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.
GPCET 13 Department Of ECE
AQUARIUM PROBE
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
GPCET 14 Department Of ECE
AQUARIUM PROBE
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
GPCET 15 Department Of ECE
AQUARIUM PROBE
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.
GPCET 16 Department Of ECE
AQUARIUM PROBE
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
GPCET 17 Department Of ECE
AQUARIUM PROBE
“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.
GPCET 18 Department Of ECE
AQUARIUM PROBE
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.
GPCET 19 Department Of ECE
AQUARIUM PROBE
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.
GPCET 20 Department Of ECE
AQUARIUM PROBE
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:
GPCET 21 Department Of ECE
AQUARIUM PROBE
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
GPCET 22 Department Of ECE
AQUARIUM PROBE
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
GPCET 23 Department Of ECE
AQUARIUM PROBE
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
GPCET 24 Department Of ECE
AQUARIUM PROBE
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).
GPCET 25 Department Of ECE
AQUARIUM PROBE
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
GPCET 26 Department Of ECE
AQUARIUM PROBE
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.
GPCET 27 Department Of ECE
AQUARIUM PROBE
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
GPCET 28 Department Of ECE
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
GPCET 29 Department Of ECE
AQUARIUM PROBE
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
GPCET 30 Department Of ECE
AQUARIUM PROBE
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
GPCET 31 Department Of ECE
AQUARIUM PROBE
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
GPCET 32 Department Of ECE
AQUARIUM PROBE
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.
GPCET 33 Department Of ECE
AQUARIUM PROBE
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
GPCET 34 Department Of ECE
7805
AQUARIUM PROBE
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
GPCET 35 Department Of ECE
AQUARIUM PROBE
Features:
Low leakage current
Flat junction capacitance
High mechanical strength
GPCET 36 Department Of ECE
AQUARIUM PROBE
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.
GPCET 37 Department Of ECE
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
GPCET 38 Department Of ECE
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
GPCET 39 Department Of ECE
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).
GPCET 40 Department Of ECE
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.
GPCET 41 Department Of ECE
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:
GPCET 42 Department Of ECE
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.
GPCET 43 Department Of ECE
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.
GPCET 44 Department Of ECE
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
GPCET 45 Department Of ECE
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.
GPCET 46 Department Of ECE
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.
GPCET 47 Department Of ECE
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
GPCET 48 Department Of ECE
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.
GPCET 49 Department Of ECE
AQUARIUM PROBE
COST DETAILS:
GPCET 50 Department Of ECE
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
GPCET 51 Department Of ECE
AQUARIUM PROBE
PHOTO COPIES
GPCET 52 Department Of ECE
AQUARIUM PROBE
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
GPCET 53 Department Of ECE
Top Related