The document describes a temperature controller circuit that uses a thermistor for temperature sensing. The circuit uses an operational amplifier (LM741) to compare the voltage from the thermistor to a reference voltage and control a transistor switch. When the temperature sensed by the thermistor exceeds the threshold, the transistor powers a CPU fan for cooling. The circuit aims to maintain precise temperature regulation using low-cost components like the thermistor, operational amplifier, transistor and fan. It has applications in appliances, industrial processes and more where consistent temperature is important.

1. TEMPERATURE
CONTROLLER
By Samved Chanda
Mohit Choudhary
Chitra Rao
Harshal Lokhande
Project Guide: Prof. Keshav Choughule

2. CONTENTS
• Introduction
• Circuit Diagram
• Operation and Working
• Components Required
• Advantages and Disadvantages
• Implementation on breadboard
• Applications
• Conclusion
• Literature Survey
• References

3. INTRODUCTION
• A temperature controller is a device used to maintain a specific temperature within a
given system or environment. It achieves this by continuously monitoring the
temperature and adjusting a heating or cooling element as needed to keep the
temperature at the desired set-point.
• Temperature controllers are used in various applications, including industrial processes,
HVAC systems, laboratory equipment, and home appliances, to ensure precise and
consistent temperature regulation.
• They play a crucial role in enhancing product quality, safety, and energy efficiency.
• In this mini project we are designing a compact temperature controller using thermistor
as its temperature sensing element

4. CIRCUIT DIAGAM

5. OPERATION AND WORKING
• Here Operational Amplifier compares Reference voltage at non inverting input and inverting input
and controls output voltage by using op-amp output transistor BC547 acts as switch to connect or
disconnect DC fan from power supply.
• Variable Resistor VR1 is connected across power supply and variable pin is connected to the Non
inverting input of IC 741 and then NTC thermistor is connected between the power supply
through R1 Resistor and also connected with Inverting Input of IC 741. Operational amplifier also
uses the same power supply source and output is connected to the Q1 transistor base through R2
Resistor. 12V DC fan is conned with positive supply and Q1 transistor collector terminal, here the
Q1 transistor acts as switch. When the temperature increase and reaches the threshold then op-
amp gives differential voltage and makes Q1 transistor turn ON then DC fan gets ground supply
and starts to run. If the temperature level below the threshold then op-amp gives zero output
then Q1 transistor stays in turn OFF condition and DC fan don’t get bias to run and so it remains in
off condition.

6. COMPONENTS REQUIRED
• Thermistor NTC 10KΩ
• Operational Amplifier IC LM741
• DC CPU Fan 9V
• Transistor BC547 NPN
• Resistors 4.7KΩ, 39Ω each one
• Variable Resistor 10KΩ
• Diode 1N4007
• Battery 9V

7. THERMISTOR(NTC 10K Ω)
• A NTC (Negative Temperature Coefficient) 10k ohm thermistor is a type of temperature
sensor that exhibits a decrease in resistance as its temperature increases. Here is some
information about it:
• Resistance-Temperature Relationship: NTC thermistors follow the principle that their
resistance decreases as the temperature rises. The "10k" in its name indicates that the
thermistor has a nominal resistance of 10,000 ohms (10k ohms) at a specific reference
temperature, typically 25 degrees Celsius (77 degrees Fahrenheit).
• Non-Linear Response: NTC thermistors have a non-linear response to temperature
changes, which means that their resistance change is not constant but varies significantly
with temperature. The rate of change in resistance is often described by a parameter
called the Beta (β) value.

8. • Why did we use this component?
• Accuracy: NTC thermistors can provide high sensitivity and accuracy in temperature
measurement, especially within a specific temperature range. However, their non-linear response
may require calibration for precise temperature control.
• Temperature Range: The temperature range over which an NTC 10k ohm thermistor can be used
effectively depends on its specific characteristics, but it's typically suitable for a range of -50°C to
150°C (-58°F to 302°F).
• We used this component for its overall simplicity, its high sensitivity and it being inexpensive.
Also Thermistor has good temperature range making it really suitable for this project.

9. OPERATIONALAMPLIFIER
• The LM741 is a widely used operational amplifier (op-amp) integrated circuit
that was first introduced by Texas Instruments in the late 1960s. Here's some
information about the LM741:
• Function: An operational amplifier is an electronic component that amplifies
the difference in voltage between two input pins. The LM741 is specifically
designed for general-purpose amplification and signal processing applications.
• Pin Configuration: The LM741 typically comes in an 8-pin dual-in-line (DIP)
package. It has two input pins (inverting and non-inverting), one output pin,
and pins for power supply and ground connections.

10. • Why did we use this component?
• As the thermistor provides us with weak analog signal IC LM741(more commonly known as UA741)
acts a comparator in this circuit.
• ThIs IC takes two reference voltages from input pin 2 and 3 and compare them, after which an
amplified output signal is given at output pin 6.
• Thus, by comparing two reference voltages this IC provides us with an amplified output signal
making it a comparator
• Other advantages of IC LM741 are that it has a wide operation range and can operate in negative
voltage as well as in various environmental condition.
• Here is a well labelled pinout diagram of
IC LM741:

11. 12V DC CPU FAN
• The main purpose of this fan is to work as the cooling element of the
circuit.
• The output of the whole circuit is obtained on this 12V DC Fan.
• A Diode is attached in parallel to the this fan to prevent any leakage
current from damaging the thermistor.
• This component will be used to show the output, when temperature
change occurs at thermistor(input). This helps maintain low
temperatures.

12. TRANSISTOR (BC547 NPN)
• The BC547 is a widely used NPN (Negative-Positive-Negative) bipolar
junction transistor.
• Function: It is employed in electronic circuits for tasks like signal
amplification, switching, and voltage regulation.
• Pinout: The BC547 has three pins: collector (C), base (B), and emitter (E),
with current flowing from the collector to the emitter when the base is
biased correctly.
• Voltage Ratings: It has modest voltage and current ratings, suitable for
low-power applications.

13. • Why did we use this component?
• Main purpose of the transistor is to work as a switch and to redirect current from the Amplifier IC
LM741
• The transistor receives current at the base which which gets redirected towards the collector
terminal which is further connected to the DC Fan.
• A pinout and circuit diagram of npn transistor BC547 is given below:

14. DIODE(1N4007)
• Type: The 1N4007 is a rectifier diode, which means it's commonly used for
converting alternating current (AC) to direct current (DC) in electronic
circuits.
• Voltage Rating: It has a peak reverse voltage (also known as peak inverse
voltage or PIV) of 1000 volts. This means it can handle up to 1000V in the
reverse-biased direction.
• Current Rating: The forward current rating is typically 1 ampere (A), making
it suitable for low to moderate current applications.
• Polarity: Like all diodes, the 1N4007 is polarized, meaning it has an anode
and a cathode. Current should flow from the anode (positive) to the
cathode (negative) for it to function properly.
• Applications: It's commonly used in power supply circuits, voltage
regulation, and general-purpose rectification where moderate voltage and
current requirements exist.

15. RESISTANCES(39 Ω & 4.7K Ω)
• 1. 39 Ohm Resistor:
• Resistance Value: 39 ohms (Ω).
• Color Code: In the color code system for resistors, this value might be
represented by bands like orange (3), white (9), and a multiplier band for the
number of zeros, which is often gold (0.1).
• Applications: Used in various circuits, often in current limiting or voltage
dividing applications.
• 2. 4.7 Kilo ohm Resistor:
• Resistance Value: 4.7 kilohms (kΩ), which is equivalent to 4,700 ohms.
• Color Code: The color bands for this value might include yellow (4), violet (7),
and an appropriate multiplier band, which is typically red (1000).
• Applications: Commonly used for voltage dividers, biasing transistors, and in
various electronic circuits where a moderate amount of resistance is needed.

16. VARIABLE RESISTOR(10K Ω)
• Resistance Value: 10,000 ohms or 10 kilohms (10kΩ). This
means that its resistance can be adjusted from 0 ohms to
10,000 ohms using its knob or slider.
• The main purpose of this resistor is to limit the amount of
current from reaching the fan
• It also keeps the IC from sudden voltage gain.
• Type: Variable resistors of this value are commonly available in
both rotary (knob) and linear (slider) forms, depending on the
application.

17. ADVANTAGES
• Accuracy: Thermistors provide precise temperature measurements, allowing for tight
control of temperature within a desired range.
• Cost-Effective: Thermistors are relatively inexpensive compared to other temperature
sensing devices like RTDs (Resistive Temperature Detectors) or thermocouples.
• Fast Response: They respond quickly to changes in temperature, making them suitable
for applications that require rapid temperature adjustments.
• Compact Size: Thermistors are small and can be easily integrated into various devices
and systems without taking up much space.
• Energy Efficiency: Temperature controllers using thermistors can help save energy by
maintaining temperatures within a narrow range, reducing unnecessary heating or
cooling.

18. DISADVANTAGES
• Limited Temperature Range: Thermistors have a limited temperature range compared to other
sensors, so they may not be suitable for extremely high or low-temperature applications.
• Non-Linear Response: Their resistance-temperature relationship is non-linear, requiring additional
calibration and compensation to achieve accurate readings.
• Sensitivity to Voltage Changes: Thermistors are sensitive to voltage fluctuations, which can affect
their accuracy if the power supply isn't stable.
• Aging: Over time, thermistors can drift and become less accurate, necessitating periodic
calibration or replacement.
• Variability: There can be variations in thermistor characteristics between different units, which
may require individual calibration.

19. IMPLEMENTATION ON BREADBOARD

21. APPLICATIONS
• Home Thermostats: Thermistors are commonly used in home heating and cooling systems to
maintain a comfortable indoor temperature.
• Medical Devices: They are used in medical equipment like incubators and blood temperature
monitors to ensure safe and stable conditions.
• Automotive: Thermistors help control engine temperature, cabin climate, and cooling systems in
vehicles.
• Food Industry: They play a role in food processing and storage, ensuring that temperatures
remain within safe limits.
• Environmental Monitoring: Thermistors are used in weather stations and environmental sensors
to measure temperature

22. CONCLUSION
• In conclusion, our exploration of the temperature controller using a thermistor reveals a
promising project with practical applications in various fields. While the thermistor's sensitivity
and cost-effectiveness make it an attractive choice, we must be mindful of its non-linear behavior
and susceptibility to damage. With its potential to enhance temperature regulation in everyday
devices, medical equipment, and industrial processes, our mini-project aims to harness the power
of this simple yet efficient sensor to improve our daily lives.

23. LITERATURE SURVEY
Sr.no. Title of article/Journal Authors Name Pub. Year
1 An Analog Frontend Using
Feedback Compensation
For Thermistor
Linearization
Manvendra Sharma,
Thomaskutty Mathew
2022
2 High Accuracy Wide Range
Resistance Measurement
For Thermistor Sensor
Monitoring
Stefano Nieddu 2012
3 Changing technology
banish the 741[op amp]
J.L.Schmazel 1998
4 The response of 741 op
amps to very short pulses
V.G.Ruediger 1980

24. REFERENCES
• Electronics Devices And Circuits [J.S.Katre]
• https//electronics.stackexchange.com

25. THANK YOU