Automatic temperature controlled fan

Automatic temperature controlled fan

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CHAPTER 1 INTRODUCTION

1.1 AUTOMATIC CONTROL In the fast-paced world, there is little time for every processes and greater need for automatically operating systems. The idea for an Automatic temperature controlled fan stems from this need. Automatic temperature controlled fan allow you to experience total freedom by eliminating manual operations for cooling a system during a process. The temperature of all types of machines used in an industry will increase due to its continues working. It is necessary to cool the machines for their long life and better working. Automatic temperature controlled fan will cool the surroundings according to the surrounding temperature.

1.2 WHAT IS AUTOMATIC TEMPERATURE CONTROLLED FAN? FAN? Automatic temperature controlled fan is a device, that can be used for cooling the surroundings of a machine or room automatically with the changes in the temperature of the surroundings. It uses a thermister for sensing the temperature and a fan for providing cooling. When the temperature is raised above a fixed point the device automatically switch on the fan and there by reduces the temperature. It is an efficient device that can be used for cooling purposes of the machines in an industry. It can also be used with ceiling fans in a house for cooling a room automatically according to the temperature.

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1.2.2 ADVANTAGES OF AUTOMATIC TEMPERATURE CONTROLLED FAN

1. Simple and easy to construct. 2. Low cost. 3. Fully automatic. 4. Can be used for a number of applications. 5. Besides, since an optocoupler is used, the control circuit is fully isolated from power circuit, thus providing added safety. 6. For any given temperature the speed of fan can be adjusted to a desired value.

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CHAPTER 2 BLOCK DIAGRAM

Temperature sensor

Current to Voltage converter

amplification

comparator

Load

2.1. Block diagram description

2.1.1 Temperature sensor Here we use a NTC (negative temperature coefficient) thermistor. The resistance of the thermistor decreases with rise in temperature and resistance increases with fall of temperature. The value of thermistor resistance at 25°C is about 1 kilo-ohm.

2.1.2 Current to voltage converter There is a current to voltage converter for converting temperature variations into voltage. Here an op amp is connected as I to v converter. It converts temperature variations into voltage.

2.1.3 Amplification To amplify the change in voltage due to change in temperature, instrumentation amplifier Formed by op-amps A2, A3 and A4 are used. Resistor R2 and zener diode D1 combination is used for generating reference voltage as we want to amplify only change in voltage due to the change in temperature.

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2.1.4 Comparator Op-amp μA741 (IC2) works as a comparator. One input to the comparator is the output from the instrumentation amplifier while the other input is the stepped do wn, rectified and suitably attenuated sample of AC voltage. This is a negative going pulsating DC voltage. Comparator compares the two inputs to give output.

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2.1.5Load The output from the comparator is coupled to an optocoupler, which in turn controls the AC power delivered to fan (load).

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CHAPTER 3 AUTOMATIC TEMPERATURE CONTROLLED FAN

3.1 POWER SUPPLY 3.1.1 TRANSFORMER

In brief a transformer is device that 

Transfers electric power from one circuit to another



Does so without any change of frequency



Accomplishes this by electromagnetic induction



Contains to electric circuits which are linked by mutual induction

The power supply for this project requires a step-down transformer with 250 V and output with +12 V&-12V.

3.1.2 RECTIFIER

The rectifier circuit is the heart of a power supply. We use full wave bridge rectifier. The description is as follows



Full wave bridge rectifier

Fig 3.1 Rectifier

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During the positive half cycles of the secondary voltage diodes D2 and D4 are conducting and diodes D1 and D3 not conducting. Therefore, current flows through the secondary winding, diode D2, load resister RL and D4. During the negative half cycles D1 and D3 are conducting and diodes D2 and D4 are not conducting. Therefore, current flows through the secondary winding, diode D1, load resistor RL and diode D3.In both cases, the current passes through the load resistor in the same direction. The rectifier used in this project is bridge rectifier.

3.1.3 FILTER

The rectifier used in this problem is shunt capacitor filter. A filter circuit is a device which removes the ac component of rectifiers output but allows the dc component to reach the load.

The filter circuit should be installed between the rectifier and the load. A filter circuit is generally a combination of inductor (L) and capacitor (C). The filtering action of inductor and capacitor depends upon the basic electrical principles. A capacitor passes ac readily but does not pass dc at all. On the other hand the inductor opposes ac but allows dc to pass through it. It then becomes clear that suitable network of inductor and capacitor can effectively remove the ac component to reach the load.

3.1.4 VOLTAGE REGULATORS

A voltage stabilizer is an electronic circuit that supplies a constant voltage regardless of changes in load current, temperature, and AC line voltage. Although voltage regulators can be designed using op-amps, it is quicker and easier to use IC Voltage regulators. In this project a 12V supply is needed. For this first a step down transformer with rating 230/12-0,500mA is used. The stepped down voltage is rectified using a bridge rectifier making use of four 1N4007 diodes. The output of the rectifier is filtered using a capacitive filter. Then the output is given to a voltage regulator IC 7812 to produce a 12V output.

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Regulator IC (LM 7812)

The LM7812 monolithic 3-terminal positive voltage regulators. They are intended as fixed voltage regulators in a wide range of applications. In addition to use as fixed voltage regulators, these devices can be used with external components to obtain adjustable output voltages and currents. Considerable effort was expended to make the entire series of regulators easy to use and minimize the number of external components.

Fig 3.2 LM 7812

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3.2

CIRCUIT

DIAGRAM

9

OF

AUTOMATIC

CONTROLLED FAN &IT’S EXPLANATION

Fig 3.3 CIRCUIT DIAGRAM

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TEMPERATURE


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In this circuit, the temperature sensor used is an NTC thermistor, i.e. one having a negative temperature coefficient. The value of thermistor resistance at 25°C is about 1 kilo-ohm. Op-amp A1 essentially works as I to V (current-to-voltage) converter and converts temperature variations into voltage variations. To amplify the change in voltage due to change in temperature, instrumentation amplifier formed by op-amps A2, A3 and A4 Misused. Resistor R2 and zener diode D1 combination is used for generating reference voltage as we want to amplify only change in voltage due to the change in temperature. Op-amp μA741 (IC2) works as a comparator. One input to the comparator is the output from the instrumentation amplifier while the other input is the stepped down, rectified and suitably attenuated sample of AC voltage. This is a negative going pulsating DC voltage. It will be observed that with increase in temperature, pin 2 of IC2 goes more and more negative and hence the width of the positive going output pulses (at pin 6) increases linearly with the temperature. Thus IC2 functions as a pulse width modulator in this circuit. The output from the comparator is coupled to an optocoupler, which in turn controls the AC power delivered to fan (load).The circuit has a high sensitivity and The output RMS voltage (across load) can be varied from 120V to 230V (for a temp.range of 22°C to 36°C), and hence wide variations in speed are available. Also note that speed varies linearly and not in steps. Besides, since an optocoupler is used, the control circuit is fully isolated from power circuit, thus providing added safet y. Note that for any given temperature the speed of fan (i.e. voltage across load) can be adjusted to a desired value by adjusting potentiometer.

3.3 COMPONENTS 3.3.1 RESISTOR

A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant of proportionality is known as the resistance R, since, with

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a given voltage V, a larger value of R further "resists" the flow of current I as given by Ohm's law I = V/R

The ohm (symbol: Ω) is the SI unit of electrical resistance, named after George Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ =

10−3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106 Ω) are also in common usage. 3.3.2 CAPACITORS

A capacitor (formerly known as condenser ) is a device for storing electric charge. The forms of practical capacitors vary widely, but all contain at least two conductors separated by a non-conductor. Capacitors used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes. A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops in the dielectric that stores energy and produces a mechanical force between the conductors. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.

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3.3.3VARIABLE RESISTOR (PRESET)

This type of variable resistor (a preset) is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than normal variable resistors so they are often used in projects to reduce the cost.

Fig 3.6 Variable Resistor 3.3.5optocoupler

In electronics, an opto-isolator, also called an optocoupler, photocoupler, or optical isolator, is "an electronic device designed to transfer electrical signals by utilizing light waves to provide coupling with electrical isolation between its input and output". The main purpose of an opto-isolator is "to preventhigh voltages or rapidly changing voltages on one side of the circuit from damaging components or distorting transmissions on the other side." Commercially available opto-isolators withstand input-to-output voltages up to 10 kV[3] and voltage transients with speeds up to 10 kV/μs.

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An opto-isolator contains a source (emitter) of light, almost always a near infrared lightemitting diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical channel), and a photosensor, which detects incoming light and either generates electric energy directly, ormodulates electric current flowing from an external power supply. The sensor can be a photoresistor, a photodiode, a phototransistor, a silicon-controlled rectifier (SCR) or a triac. Because LEDs can sense light in addition to emitting it, construction of symmetrical, bidirectional opto-isolators is possible. An optocoupled solid state relay contains a photodiode opto-isolator which drives a power switch, usually a complementary pair of MOSFET transistors. Aslotted optical switch contains a source of light and a sensor, but its optical channel is open, allowing modulation of light by external objects obstructing the path of light or reflecting light into the sensor.

3.3.6Triac BT136

TRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component which can conduct current in either direction when it is triggered (turned on), and is formally called a bidirectional triode thyristor or bilateral triode thyristor. A TRIAC is approximately equivalent to two complementary unilateral thyristors (one is anode triggered and another is cathode triggered SCR) joined inantiparallel (paralleled but with the polarity reversed) and with their gates connected together. It can be triggered by either a positive or a negative voltage being applied to its gate electrode (with respect to A1, otherwise known as MT1). Once triggered, the device continues to conduct until the current through it drops below a certain threshold value, the holding current, such as at the end of a half-cycle of alternating current (AC) mains power. This makes the TRIAC a very convenient switch for AC circuits, allowing the control of very large

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power flows with mill ampere-scale control currents. In addition, applying a trigger pulse at a controllable point in an AC cycle allows one to control the percentage of current that flows through the TRIAC to the load (phase control).

3.3.4Operational amplifiers An op amp is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals. Operational amplifiers are important building blocks for a wide range of electronic circuits. They had their origins in analog

computers where they were used in many

linear, non-linear and frequency-dependent circuits. Their popularity in circuit design largely stems from the fact that characteristics of the final op-amp circuits with negative feedback (such as their gain) are set by external components with little dependence on temperature changes and manufacturing variations in the op-amp itself. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps may be packaged as components, or used as elements of more complex integrated circuits. The op-amp is one type of differential amplifier.

The circuit symbol for an op-amp is shown where:



: non-inverting input



: inverting input

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

: output



: positive power supply



: negative power supply

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

Operation The amplifier's differential inputs consist of a

input and a

input, and ideally the op-

amp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the op-amp is given by the equation,

where

is the voltage at the non-inverting terminal,

is the voltage at the inverting

terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input). The magnitude of AOL is typically very large — 10,000 or more for integrated circuit opamps — and therefore even a quite small difference between

and

drives the amplifier

output nearly to the supply voltage. This is called saturation of the amplifier. Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp acts as a comparator. If the inverting input is held at ground (0 V) directly or by a resistor, and the input voltage V in applied to the non-inverting input is positive, the output will be maximum positive; if V in is negative, the output will be maximum negative. Since there is no feedback from the output to either input, this is an open loop circuit acting as a comparator.

An op-amp with negative feedback (a non-inverting amplifier)

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If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input. The closed loop feedback greatly reduces the gain of the amplifier. If negative feedback is used, the circuit's overall gain and other parameters become determined more by the feedback network than by the op-amp itself. If the feedback network is made of components with relatively constant, stable values, the unpredictability and inconstancy of the op-amp's parameters do not seriously affect the circuit's performance. Typically the op-amp's very large gain is controlled by negative feedback, which largely determines the magnitude of its output ("closed-loop") voltage gain in amplifier applications, or the transfer function required (in analog computers). High input impedance at the input terminals and low output impedance at the output terminal(s) are important typical characteristics. For example, in a non-inverting amplifier (see the figure on the right) adding a negative feedback via the voltage divider R f,R g reduces the gain. Equilibrium will be established when Vout is just sufficient to reach around and "pull" the inverting input to the same voltage as Vin. The voltage gain of the entire circuit is determined by 1 + R f /R g. As a simple example, if Vin = 1 V and R f = R g, Vout will be 2 V, the amount required to keep V – at 1 V. Because of the feedback provided by R f ,R g this is a closed loop circuit. Its overall gain Vout / Vin is called the closed-loop gain A CL. Because the feedback is negative, in this case ACL is less than the A OL of the op-amp.

Op-amp characteristics Ideal op-amps

An equivalent circuit of an operational amplifier that models some resistive non-ideal parameters.

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An ideal op-amp is usually considered to have the following properties, and they are considered to hold for all input voltages: 

Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as open loop gain A OL goes to infinity).



Infinite voltage range available at the output (v out) (in practice the voltages available from the output are limited by the supply voltages

and

). The power supply sources

are called rails. 

Infinite bandwidth (i.e., the frequency magnitude response is considered to be flat everywhere with zero phase shift).



Infinite input impedance (so, in the diagram, from



to

, and zero current flows

).

Zero input offset voltage (i.e., when the input terminals are shorted so that

, the

output is a virtual ground or vout = 0). 

Infinite slew rate (i.e., the rate of change of the output voltage is unbounded) and power bandwidth (full output voltage and current available at all frequencies).



Zero output impedance (i.e., R out = 0, so that output voltage does not vary with output current).



Infinite Common-mode rejection ratio (CMRR).

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Op amp as instrumentation amplifier

Although the instrumentation amplifier is usually shown schematically identical to a standard op-amp, the electronic instrumentation amp is almost always internally composed of 3 op-amps. These are arranged so that there is one op-amp to buffer each input (+,−), and one to produce the desired out put with adequate impedance matching for

the function. The most commonly used instrumentation amplifier circuit is shown in the figure. The gain of the circuit is

The rightmost amplifier, along with the resistors labeled R 2 and R 3 is just the standard differential amplifier circuit, with gain =R 3 / R 2 and differential input resistance = 2·R 2. The two amplifiers on the left are the buffers. With R gain removed (open circuited), they are simple unity gain buffers; the circuit will work in that state, with gain simply equal to R 3 / R 2 and high input impedance because of the buffers. The buffer gain could be increased by putting resistors between the buffer inverting inputs and ground to shunt away some of the negative feedback; however, the single resistor R gain between the two inverting inputs is a much more elegant method: it increases the differential-mode gain of the buffer pair while leaving the Dept. ECE, CEMP


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common-mode gain equal to 1. This increases the common-mode rejection ratio (CMRR) of the circuit and also enables the buffers to handle much larger commonmode signals without clipping than would be the case if they were separate and had the same gain. Another benefit of the method is that it boosts the gain using a single resistor rather than a pair, thus avoiding a resistor-matching problem (although the twoR 1s need to be matched), and very conveniently allowing the gain of the circuit to be changed by changing the value of a single resistor. A set of switch-selectable resistors or even a potentiometer can be used for R gain, providing easy changes to the gain of the circuit, without the complexity of having to switch matched pairs of resistors. The ideal common-mode gain of an instrumentation amplifier is zero. In the circuit shown, common-mode gain is caused by mismatches in the values of the equallynumbered resistors and by the mis-match in common mode gains of the two input op-amps. Obtaining very closely matched resistors is a significant difficulty in fabricating these circuits, as is optimizing the common mode performance of the input op-amps. An instrumentation amp can also be built with 2 op-amps to save on cost and increase CMRR, but the gain must be higher than 2 (+6 dB).

Current to voltage converter

A current-to-voltage converter (or transimpedance amplifier) is an electrical device that takes an electric current as an input signal and produces a corresponding voltage as an

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output signal. Three kinds of devices are used in electronics: generators (having only outputs), converters (having inputs and outputs) and loads (having only inputs). Most frequently, electronic devices use voltage as input/output quantity, as it generally requires less power consumption than using current. In some cases, there is a need for converters having current as the input and voltage as the output. A typical situation is the measuring of current using instruments having voltage inputs.

A current-to-voltage

converter is

a circuit that

performs current to voltage transformation. In electronic circuitry operating at signal voltages, it usually changes the electric attribute carrying information from current to voltage. The converter acts as a linear circuit with transfer ratio k = V OUT/IIN, called the transimpedance, which has dimensions of [V/A] (also known as resistance). That is why the active version of the circuit is also referred to as a transresistance or transimpedance amplifier. Typical applications of current-to-voltage converter are measuring currents by using instruments having voltage inputs, creating current-controlled voltage sources, building various passive and active voltage-to-voltage converters, etc. In some cases, the simple passive current-to-voltage converter works well; in other cases, there is a need of using active current-to-voltage converters. There is a close interrelation between the two versions - the active version has come from the passive one. Ideal current-to-voltage converters have zero input resistance (impedance), so that they actually short the input source. Therefore, in this case, the input source has to have some resistance; ideally, it has to behave as a constant current source. Otherwise, the input source and the current-to-voltage converter can saturate.

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CHAPTER 4 PCB DESIGN

4.1 INTRODUCTION TO PCB DESIGN The PCB design starts right from the selection of the laminates .The two main types of base laminate are epoxy glass and phenolic paper laminates are generally used for simple circuits. Though it is very cheap and can easily be drilled, phenol paper has poor electrical characteristics and it absorbs more moisture than epoxy glass. Epo xy glass has higher mechanical strength. The important properties that have to be considered for selecting the PCB substrate are the dielectric strength, insulation resistance, water absorption property, coeff. of thermal expansion, shear strength, hardness, dimensional stability etc. 4.1.1 MANUFACTURING PROCESS

The steps involved in manufacture are a. Artwork preparation. b. Resist preparation. c. Resist application fixing. d. Acid etches.

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e. Cleaning and inspection. f. Resist removal. 4.1.2 PCB FABRICATION

The fabrication of a PCB basically of four steps. a. Preparing the PCB pattern. b. Transferring the pattern onto the PCB. c. Developing the PCB. d. Finishing ie) drilling, cutting, smoothing, turning etc. a. Preparing the PCB pattern.

Pattern designing is the primary step in fabricating a PCB in this step, all interconnection between the components in the given circuit are converted into PCB tracks several factors such as positioning, the diameter of holes, the area that each component would occupy, the type of end terminal should be considered. b. Transferring the PCB Pattern

The copper side of the PCB should be thoroughly cleaned with the help of alcoholic spirit or petrol must be completely free from dust and other contaminants. The mirror image of the pattern must be carbon copied and to the laminate the complete pattern may now be made each resistant with the screen printing technology. c. Developing the PCB

In this developing all excessive copper is removed from the board and only the printed pattern is left behind. About 100ml of tape water should be heated to 75 ° C and

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30.5 grams of FeCl3 added to it, the mixture should be thoroughly stirred and a few drops of HCl may be added to speed up the process. The board with its copper side facing upward should be placed in a flat bottomed plastic tray and the aqueous solution of FeCl2 poured in the etching process would take 40 to 60 min to complete. After etching the board it should be washed under running water and then held against light .the printed pattern should be cleanly visible. The paint should be removed with the help of thinner.

d. Finishing Touches

After the etching is completed, hole of suitable diameter should be drilled, then the PCB may be tin plated using an ordinary 35 Watts soldering rod along with the solder core, the copper side may be given a coat of varnish to prevent oxidation. 

Drilling

Drills for PCB use usually come with either a set of collects of various sizes or a 3-Jaw chuck. For accuracy however 3- jaw chunks aren’t brilliant and small drill below 1 mm from grooves in the jaws preventing good grips.



Soldering

Begin the construction by soldering the resistors followed by the capacitors and the LEDs diodes and IC sockets. Don’t try soldering an IC directly unless you trust your

skill in soldering. All components should be soldered as shown in the figure. Now

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connect the switch and then solder/screw if on the PCB using multiple washers or spaces. Soldering it directly will only reduce its height above other components and hamper in its easy fixation in the cabinet. Now connect the battery lead. 

Assembling

The circuit can be enclosed in any kind of cabinet. Before fitting the PCB suitable holes must be drilled in the cabinet for the switch, LED and buzzer. Note that a rotary switch can be used instead of a slide type. Switch on the circuit to be desired range. It will automatically start its timing cycles. To be sure that it is working properly watch the LED flash. The components are selected to trigger the alarm a few minutes before the set limit.

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4.2 PCB LAYOUT

4.3 COMPONENTS LAYOUT

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CHAPTER 5 CONCLUSION

Technology makes life simpler and easier. Our aim was to control the temperature of a machine or room automatically according to the temperature changes. Our mini project ”AUTOMATIC TEMPERATURE CONTROLLED FAN” was an interesting subject for

us. This provided us the opportunity for familiarizing and learning various fields of electronics. As a team, each of us has dedicated our time and effort for the success of this project. We are extremely satisfied with the result o this project and we would like to develop this mini project into higher levels in future. Through this project various fields of electronics is understood, thus electronics is imbibed through this project. This circuit allows us to control the temperature automatically. since all the components used in our project are low cost and readily available our product costs very low

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BIBILIOGRAPHY

1. www.microchip.com 2. www.nationalsemiconductors.com 3. http://datasheetreference.com 4. www.electronicsforu.com 5. www.wikipedia.org

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Automatic temperature controlled fan

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