MINOR PROJECT REPORT ON

“TEMPERATURE CONTROLLED FAN”

Submitted in accordance with the curriculum requirements for

Sixth semester of the degree course in

BACHELOR OF ENGINEERING

In the branch of

ELECTRICAL ENGINEERING

of RGPV

YEAR 2010

Submitted by

HEMANT CHOUDHARY (0201EE071023)

HEMANT KUMAR SHAH (0201EE071024)

HIMANSHU SHUKLA (0201EE071025)

INDU DUBEY (0201EE071026)

KAPIL KUMAR GUPTA (0201EE071029)

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ONWARDS ON WINGS

JABALPUR ENGINEERING

COLLEGE, JABALPUR

CERTIFICATE

This is to certify that this minor project entitled as “TEMPERATURE CONTROLLED FAN” has been completed by HEMANT CHOUDHARY, HEMANT KUMAR SHAH, HIMANSHU SHUKLA, INDU DUBEY, KAPIL KUMAR GUPTA during sixth semester in partial fulfillment of the award of the degree in BACHELOR OF ENGINEERING IN ELECTRICAL ENGINEERING of RGPV during the academic year 2009-2010.

Project guide Staff in charge Head of the Department

CONTENTS2

ACKNOWLEDGEMENT INTRODUCTION COMPONENTS LIST CIRCUIT DIAGRAM WORKING IC555 555 ASTABLE CHOOSING R1, R2 AND C1 ASTABLE OPERATION DUTY CYCLE CONCLUSION

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ACKNOWLEDGEMENT

We express our sincere thanks and deep sense of gratitude towards Mr. A.K. Kori, under whose able guidance we were able to implement this thought of ours into a reality.

His timely and incisive review, comments and suggestions throughout the project enabled us to modify the project before things went out of our hand. We thank him for everything, from conception of getting things done practically and a lot of steps along the way, which helped us in overcoming our difficulties and making the project a successful endeavour.

We are also grateful to Dr. A.K. Sharma, Head of Deptt., Electrical engineering. He helped us immensely by providing us with all the equipment important for our project.

INTRODUCTION

An automatic temperature controlled fan system is designed to detect the unwanted presence of tempetature by monitoring

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environmental changes associated with power electronic equipment working at higher current ratings and for long time. In general, a temperature controlled fan speed system is either classified as automatic, manually activated, or both.

Automatic temperature controlled variable speed of fan systems have become increasingly sophisticated and functionally more capable and reliable in recent years. They are designed to fulfil two general requirements: protection of electronic equipment and assets and protection of life. As a result of institutes and industries, the equipment safety aspect of automatic cooling has become a major factor in the last two decades. These systems may have applications in many systems where power electronic equipment produces heat and regular cooling is required for proper and efficient working of equipments such as computers, laptops, VCRs, DVD players, projectors, etc.

This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain. Regardless of type, application, complexity, or technology level, TCF system is comprised of four basic elements:

1. Initiating devices 2. Control panel 3. Signalling devices 4. Power supply

COMPONENTS LIST

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RESISTORS (+5% CARBON,1/4W) R1 - 1KΩ 1NOS R2 - 4.7KΩ 1NOS R3 - 56KΩ 1NOS R4 - 56KΩ 1NOS VR1 - 100KΩ 1NOS

CAPACITORS C1 – 0.04 µF 1NOSC2 - 0. 01 µF 1NOS C3 - 220 µF/25V 1NOS C4 - 10 µF/25V 1NOS MISC IC1 - IC555 1NOS T1 - BC148 1NOS FAN (3.5V, DC, 1200 RPM) 1NOS

D1 - DR25 GER DIODE 1NOS TRANSFORMER (INPUT 230V A.C., OUTPUT 9-0-9 V A.C.)

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CIRCUIT DIAGRAM

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WORKING The temperature controlled fan circuit here is designed with the

principle of working of an astable multivibrator using IC 555. An astable multivibrator is a circuit which generates continuous pulses at the output terminal for the designed frequency. The generated frequency changes the speed of the fan when connected.

In the above circuit the sensor used is a germanium diode DR25 which is reverse biased in the circuit. The reverse resistance of the diode is very high and current cannot pass through the diode at room temperature.

In the astable multivibrator of our circuit, the reset pin is connected ground. At this condition the astable multivibrator cannot produce frequency. At room temperature transistor T1 on since the base of the transistor T1 gets enough potential since the diode is not conducting and offering a high resistance.

When temperature of the diode increases in case of temperature rise, the junction of the diode breakdowns and start conducting. At about 70˚c its resistance drop to a value below 1KΩ. This stops T1 conducting since base of t1 is now connected directly to ground through diode D1 and ground connection to the pin 4 of IC 555 is now removed and is now connected to the Vcc through R2. Now astable multivibrator is activated and starts generating frequency which changes the speed of the fan.

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IC 555

The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. With just a few external components it can be used to build many circuits, not all of them involve timing!

A popular version is the NE555 and this is suitable in most cases where a '555 timer' is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams on this page show a 555, but they could all be adapted to use one half of a 556.

Fig. Actual pin arrangements

Low power versions of the 555 are made, such as the ICM7555, but these should only be used when specified (to increase battery life) because their maximum output current of about 20mA (with a 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555.

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The circuit symbol for a 555 is a box with the pins arranged to suit the circuit diagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually just the pin numbers are used and they are not labelled with their function. The 555 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum). Standard 555 ICs create a significant 'glitch' on the supply when their output changes state. This is rarely a problem in simple circuits with no other ICs, but in more complex circuits a smoothing capacitor (eg 100µF) should be connected across the +Vs and 0V supply near the 555 or 556. The input and output pin functions are described briefly below and there are fuller explanations covering the various circuits:

Astable - producing a square wave Monostable - producing a single pulse when triggered Bistable - a simple memory which can be set and reset Buffer - an inverting buffer (Schmitt trigger)

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Inputs of 555

Fig. Example circuit symbol

Trigger input: when input < 1/3 Vs ('active low') this makes the output high (+Vs). It monitors the discharging of the timing capacitor in an astable circuit. It has a high input impedance > 2M Ω.

Threshold input: when input > 2/3 Vs ('active high') this makes the output low (0V)*. It monitors the charging of t he timing capacitor in astable and monostable circuits. It has a high input impedance > 10M Ω.

* providing the trigger input is > 1/3 Vs, otherwise the trigger input will override the threshold input and hold the output high (+Vs).

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Reset input: when less than about 0.7V ('active low') this makes the output low (0V), overriding other inputs. When not required it should be connected to +Vs. It has an input impedance of about 10k Ω .

Control input: this can be used to adjust the threshold voltage which is set internally to be 2/3 Vs. Usually this function is not required and the control input is connected to 0V with a 0.01µF capacitor to eliminate electrical noise. It can be left unconnected if noise is not a problem. The discharge pin is not an input, but it is listed here for convenience. It is connected to 0V when the timer output is low and is used to discharge the timing capacitor in astable and monostable circuits.

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Output of 555

The output of a standard 555 can sink and source up to 200mA. This is more than most ICs and it is sufficient to supply many output transducers directly, including LEDs (with a resistor in series), low current lamps, piezo transducers, loudspeakers (with a capacitor in series), relay coils (with diode protection) and some motors (with diode protection). The output voltage does not quite reach 0V and +Vs, especially if a large current is flowing. To switch larger currents you can connect a transistor.

The ability to both sink and source current means that two devices can be connected to the output so that one is on when the output is low and the other is on when the output is high. The top diagram shows two LEDs connected in this way. This arrangement is used in the Level Crossing project to make the red L EDs flash alternately.

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555 Astable

Fig. 555 astable circuit

An astable circuit produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). Note that the durations of the low and high states may be different. The circuit is called an astable because it is not stable in any state. the output is continually changing between 'low' and 'high'.

Fig. 555 astable output, a square wave

(Tm and Ts may be different)

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The time period (T) of the square wave is the time for one complete cycle, but it is usually better to consider frequency (f) which is the number of cycles per second.

T = time period in seconds (s)

f = frequency in hertz (Hz)

R1 = resistance in ohms ( )

R2 = resistance in ohms ( )

C1 = capacitance in farads (F)

The time period can be split into two parts: T = Tm + Ts

Mark time (output high): Tm = 0.7 × (R1 + R2) × C1

Space time (output low): Ts = 0.7 × R2 × C1

Many circuits require Tm and Ts to be almost equal; this is achieved if R2 is much larger than R1. For a standard astable circuit Tm cannot be less than Ts, but this is not too restricting because the output can both sink and source current. For example an LED can be made to flash briefly with long gaps by connecting it (with its resistor) between +Vs and the output. This way the LED is on during Ts, so brief flashes are achieved with R1 larger than R2, making Ts short and Tm long. If Tm must be less than Ts a diode can be added to the circuit as explained under duty cycle below.

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Choosing R1, R2 and C1

R1 and R2 should be in the range 1k to 1M . It is best to choose C1 first because capacitors are available in just a few values.

Choose C1 to suit the frequency range you require (use the table as a guide).

Choose R2 to give the frequency (f) you require. Assume that R1 is much smaller than R2 (so that Tm and Ts are almost equal), then you can use: R2 = 0.7 /(f × C1)

Choose R1 to be about a tenth of R2 (1k min.) unless you want the mark time Tm to be significantly longer than the space time Ts.

If you wish to use a variable resistor it is best to make it R2. If R1 is variable it must have a fixed resistor of at least 1k in

series (this is not required for R2 if it is variable).

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Astable operation

With the output high (+Vs) the capacitor C1 is charged by current flowing through R1 and R2. The threshold and trigger inputs monitor the capacitor voltage and when it reaches 2/3Vs (threshold voltage) the output becomes low and the discharge pin is connected to 0V. The capacitor now discharges with current flowing through R2 into the discharge pin. When the voltage falls to 1/3Vs (trigger voltage) the output becomes high again and the discharge pin is disconnected, allowing the capacitor to start c harging again. This cycle repeats continuously unless the reset input is connected to 0V which forces the output low while reset is 0V. An astable can be used to provide the clock signal for circuits such as counters.

A low frequency astable (< 10Hz) can be used to flash an LED on and off, higher frequency flashes are too fast to be seen clearly. Driving a loudspeaker or piezo transducer with a low frequency of less than 20Hz will produce a series of 'clicks' (one for each low/high transition) and this can be used to make a simple metronome.

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Duty cycle

The duty cycle of an astable circuit is the proportion of the complete cycle for which the output is high (the mark time). It is usually given as a percentage. For a standard 555 astable circuit the mark time (Tm) must be greater than the s pace time (Ts), so the duty cycle must be at least 50%:

To achieve a duty cycle of less than 50% a diode can be added in parallel with R2 as shown in the diagram. This bypasses R2 during the charging (mark) part of the cycle so that Tm depends only on R1 and C1:

Tm = 0.7 × R1 × C1 (ignoring 0.7V across diode)

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Ts = 0.7 × R2 × C1 (unchanged)

Use a signal diode such as 1N4148.

Fig. 555 astable circuit with diode across R2

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CONCLUSION

A Temperature Controlled Fan is a device that detects the environmental temperature changes relating to power electronics equipments. In some cases, a temperature controlled fan system is a part of a our home air conditioning system such as in blowers, heat exhauster, room cooler etc.

When functioning properly, this circuit can be also used as fire alarm and will sound to notify people that instrument is being over heated. This type of ciruit as a fire alarm can also be used in electrical system where is chances of fireand can be found in homes, schools, churches and businesses, and function as the catalyst to saving circuits and lives. The fire alarm constructed by this project work is reliable at low cost.

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REFERENCES

CIRCUITS AND NETWORKS – A SUDHAKAR, SHYAMMOHAN S.PILLAI

OP-AMPS AND LINEAR INTEGRATED CIRCUITS – RAMAKANT A.GAYAKWAD

www.nfpa.org

en.wikipedia.org

www.redcircuits.com

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