Main Operator Cooling Fan Thermostat

1.    INTRODUCTION

Use of automatic control systems in industry is increasing day by day. Electronic circuits are employed for many operations such as automatic door openers, lighting systems, sound systems and safety devices.

The circuit we are dealing with consist of three sensors; temperature sensor, humidity sensor and remote receiver.Here with the help of sensors, the fan gets automatically on at a high temperature and turns off at a low temperature. The fan can be switched on and off with the help of any remote controller.

A sensor is a device that produces a measurable response to a change in a physical condition, such as temperature or thermal conductivity, or to a change in chemical concentration. Sensors are particularly useful for making in-situ measurements such as in industrial process control.

Sensors are an important part to any measurement and automation application. The sensor is responsible for converting some type of physical phenomenon into a quantity measurable by a data acquisition (DAQ) system.

Temperature sensors are often sensing devices embedded within some sort of insulation. However, good electrical insulation is often also good thermal insulation, and the presence of that insulation causes the sensor to respond tardily when the sensor heats up.

           

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2.    BLOCK DIAGRAM

 

3.    BLOCK DIAGRAM DESCRIPTION

3.1 TEMPERATURE SENSOR CIRCUIT

LM 35

                                                   Fig: 1

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of ±¼°C at room temperature and ±¾°C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C range (-10° with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.

FEATURES

·         Calibrated directly in ° Celsius (Centigrade)

·         Linear + 10.0 mV/°C scale factor

·         0.5°C accuracy guaranteed (at +25°C)

·         Rated for full -55° to +150°C range

·         Suitable for remote applications

·         Low cost due to wafer-level trimming

·         Operates from 4 to 30 volts

·         Less than 60 µA current drain

·         Low self-heating, 0.08°C in still air

·         Nonlinearity only ±¼°C typical

·         Low impedance output, 0.1 Ohm for 1 mA load

3.2 OPTICAL DISPLAY CIRCUIT

LM324

LOW POWER QUAD OPERATIONAL AMPLIFIER

Fig: 2

The LM124 series consists of four independent, high gain, internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.

Application areas include transducer amplifiers, DC gain blocks and all the conventional op amp circuits which now can be more easily implemented in single power supply systems. For example, the LM124 series can be directly operated off of the standard +5V power supply voltage which is used in digital systems and will easily

provide the required interface electronics without requiring the additional ±15V power supplies.

FEATURES

·         Internally frequency compensated for unity gain.

·         Large DC voltages gain 100 db.

·         Wide bandwidth (unity gain) 1 MHz (temperature compensated).

·         Wide power supply range: Single supply 3V to 32V or dual supplies ±1.5V to ±16V.

·         Very low supply current drain (700 µA)-essentially independent of supply voltage.

·         Low input biasing current 45 nA (temperature compensated).

·         Low input offset voltage 2 mV and offset current: 5 nA.

·          Input common-mode voltage range includes ground.

·          Differential input voltage range equal to the power supply voltage.

·          Large output voltage swing 0V to V+ - 1.5V

                                               

3.3TURN ON AND OFF CIRCUIT

VOLTAGE COMPARATOR

LM311      

                                                          Fig: 3

         

The LM111, LM211 and LM311 are voltage comparators that have input currents nearly a thousand times lower than devices like the LM106 or LM710. They are also designed to operate over a wider range of supply voltages: from standard ±15V op amp supplies down to the single 5V supply used for IC logic. Their output is compatible with RTL, DTL and TTL as well as MOS circuits. Further, they can drive lamps or relays, switching voltages up to 50V at currents as high as 50 mA.

Both the inputs and the outputs of the LM111, LM211 or the LM311 can be isolated from system ground, and the output can drive loads referred to ground, the positive supply or the negative supply. Offset balancing and strobe capability are provided and outputs can be wire OR'ed. Although slower than the LM106 and LM710 (200 ns response time vs 40 ns) the devices are also much less prone to spurious oscillations. The LM111 has the same pin configuration as the LM106 and LM710.

            The LM211 is identical to the LM111, except that its performance is specified over a -25°C to +85°C temperature range instead of -55°C to +125°C. The LM311 has a temperature range of 0°C to +70°C.

FEATURES

·         Operates from single 5V supply

·         Input current: 150 nA max. over temperature

·         Offset current: 20 nA max. over temperature

·         Differential input voltage range: ±30V

·         Power consumption: 135 mW at ±15V

3.4 HUMIDITY SENSOR CIRCUIT

PHOTO RESISTOR           

                                                                       

Fig: 4

The symbol for photo resistor

Fig: 5

A light dependent resistor

A photo resistor or light dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as aphotoconductor.A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire band gap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor do not have as far to jump, lower energy photons (i.e., longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms.

3.5 REMOTE RECIEVER CIRCUIT

TSOP1738

Fig: 6

TSOP1738 is an Infrared (IR) receiver which is widely used in large number of electronic products for receiving and demodulating infrared signals. It receives the infra-red rays from the device say a remote and converts the received light into current.

FEATURES

·         Photo detector and preamplifier in one package

·         Internal filter for PCM frequency

·         Improved shielding against electrical field Disturbance

·         TTL and CMOS compatibility

·         Output active low

·         Low power consumption

·         High immunity against ambient light

·         Continuous data transmission possible(up to 2400 bps)

·         Suitable burst length .10 cycles/burst

·          

CD4013

Fig: 7

The CD4013B dual D flip-flop is a monolithic complementary MOS (CMOS) integrated circuit constructed with N- and P-channel enhancement mode transistors. Each flip-flop has independent data, set, reset, and clock inputs and ``Q'' and ``Q'' outputs. These devices can be used for shift register applications, and by connecting ``Q'' output to the data input, for counter and toggle applications. The logic level present at the ``D'' input is transferred to the Q output during the positive-going transition of the clock pulse. Setting or resetting is independent of the clock and is accomplished by a high level on the set or reset line respectively.

FEATURES

·         Wide supply voltage range                 :           3.0V to 15V

·          High noise immunity                          :           0.45 VDD (typ.)

·         Low power TTL  compatibility           :           fan out of 2 driving 74L  or 1                                                                                     driving 74LS

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3.6 POWER SUPPLY

LM 7805

Fig: 8

The LM78XX series of three terminal positive regulators are available in the TO-220 package and with several fixed output voltages, making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents.

FEATURES

·         Output Current up to 1A

·         Output Transistor Safe Operating Area Protection

·          Thermal Overload Protection

·          Short Circuit Protection

4.    COMPONENTS LIST

COMPONENTS	SPECIFICATIONS	QUANTITY
TRANSISTOR	BC 547	1
DIODE	IN4007	5
IC	NE 555 LM 311 CD 4013 LM 324	1 2 1 8
RESISTOR	1K 2K 3K 6K 10K 22K 47K 100K 470K 100E 220E 390E 470E 820E	7 1 1 1 2 2 1 1 2                                    8 1 1 1 1
IR SENSOR		1
LED		10
SENSOR	LDR LM 35	1 1

5.    CIRCUIT DIAGRAM

6.    WORKING

Here we are introducing a room temperature sensing system. Use of this system can control electronic devices like fan, ac, etc. LM35, a temperature sensing device which is made up of silicon material can sense temperature in the range of 0 to 100 degree Celsius. The device activates at room temperature.

The output of the sensor is connected to an optical display circuit. This display shows the present temperature of the room. Optical display circuit consists of the comparator LM324.It compares the input voltage from the temperature sensor circuit and the defined voltage. The temperature level is indicated through the LED display.

Whenever there is an increase in temperature, such that it reaches to a maximum level (user defined). The comparator output toggle to high and the output will switch on a time delay circuit. This is maintained for a particular period and the output of the time delay pass through an MOC. MOC is an optical isolator unit. It isolates ac circuit from dc circuit. The output of MOC is connected to gate circuit of the triac and the output terminal is in series with load. Then whenever there is a decrease in room temperature, the circuit automatically switches off the triac gate signal.

Another method for turning off the circuit is by using a humidity sensor and remote switch. A humidity sensor activates at room humidity level, sensed by LDR. Increment of humidity will cut off all circuit supply.

Next part is the IR remote. This circuit is used to turn on or off the system externally. When the IR rays are received, it is transmitted to the transistor through a diode. The transistor is turned on then the potential across the collector is very low and it acts as a negative trigger to the 555 timer. The timer produces a delay determined by the resistor andcapacitor. The output of 555 is applied to the flip flop and then connected to the transistor. From there it is connected to the opto isolator.

The triac of this IR unit is connected to the triac of the fan drive circuit to turn on the system.

IR remote is a common remote switch using any type of transmitter (using ordinary remote). Remote switch is a main power switch which will manage the ON-OFF status.

7.     PCB DESIGN

           The PCB manufacturing process involves use of expensive equipments, but homebrew PCB fabrication is less expensive .It requires Intel Pentium PC,600-1200dpi laser printer with premium-quality paper or butter-paper and miscellaneous items like single side copper laminated board, Lacquer thinner, sand paper and others. The various steps involves in PCB fabrication are

7.1 PC BASED ARTWORK

           The PC based artwork consists of drawing the conductor pattern. For putting artwork on the component side of the board, flip the whole image before or while taking the print. When the pattern has been drawn, take the print out in 600 to 1200 dpi on a translucent or butter   paper. Keep the paper side on which the toner is deposited facing down over the copper laminated boards copper side and then when the board is turned component side up, the pattern on the conductor will be found properly aligned with the components. Finally we take the printout of the PCB.

7.2 TAKING THE PCB LAYOUT PRINT USING A LASER PRINTER

Take the printout of the circuit layout from a laser printer. The idea is to use a coated paper so that the toner comes loose when heated which would transfer a sharp black print on to copper laminate. Print for each of the required layers should be taken on separate paper.

 7.3 TRANSFER OF THE CONDUCTOR PATTERN

        Scrub the copper side of the copper clad laminated used for the PCB board with a sponge. The scrubbing involves removes oxidation, stains, etc. And it also makes the copper surface some-what rough which helps the toner to adhere to the

copper surface. The next step is to degrease the board thoroughly using a paper towel soaked with acetone solvent. Keep doing it until no more discoloration is seen on the paper towel. Rub hard and keep switching to clean parts of towel. Place and align the paper on the copper side, using an iron box to maximum setting on the back of the paper for at lest half a minute. If you don't apply enough heat, the film or toner may no stick or be dark enough. The removal of paper from PCB is done by putting it into hot water for 10 or more minutes. Check whether it has transferred properly onto copper plate.

              Dig the bristles on the tip of a smooth tooth brush into the holes, remove the paper part from the tight areas like drill-holes. Now cut the PCB to required size by using a hacksaw.

7.4 ETCHING

Etch the unwanted copper from the board using the ferric chloride solution for 20 or more minutes. One pint can etch at least 3.6 sq. meters of the 28gm board. Heating the etchant will speeds up the etching process. The PCB is attached to a wooden piece and dip in to the solution. Lift the PCB up and Check whether all the unwanted copper is removed. Then it is immersed in to cold water to clean. When etching is complete, board is removed from the solution and rinse it under running tap water .Acetone or lacquer thinner is used to remove the toner .Lacquer thinner is used as a solvent in painting industry. Wash the board in lacquer thinner solvent, rubbing with a paper towel, to remove the toner instantly.

7.5 DRILLING AND CLEANING

In this we had used a PCB hand drill .Use 0.8mm PCB drill bit to drill out all of the component holes. After drilling the holes scrub sponge is used to clean before soldering .After drilling and cleaning, wash the board in cold water and then dry it.

8.    PCB LAYOUT

TOP AND BOTTOM SIDE

BOTTOM SIDE

9.    SOLDERING

          Soldering is the process of joining metals by using lower melting point metal to wet or alloy with the joined surfaces. Solder is the joining material. It melts below 427’C. Soldered joints in electronic circuits will establish strong electrical connections between component leads. The popularly used solders are alloys of tin and lead that melt below the melting point of tin.

In order to make the surfaces accept the solder readily, the component terminals should be cleaned chemically or by abrasion using blades or knives. Small amount of lead coating can be done on the cleaned portion of the leads using soldering iron. This process is called tinning. Zinc chloride or ammonium chloride separately or in combination are the most commonly used fluxes. These are available in petroleum jelly as paste flux. A solder joint can at first glance to be okay, but under close examination it could be a ‘Dry Joint’. A dry joint is when either the circuit board or the leg of the component has not been properly heated to allow the solder to flow between the surfaces freely. This creates an intermittent or no electrical connection. This can also be caused by a lack of flux or if you reuse old solder.

            Quite often, reheating a bad join will cure the problem but in a lot of cases, the old solder will need to be removed and some new solder applied. The residues, which remain after the soldering, may be washed out with more water, accompanied by brushing.

Soldering iron is the tool used to melt the solder and apply at the joints in the circuit. It operates in 230V mains supply. The iron bit at the tip of it gets heated up within a few minutes. 50W and 25W soldering irons are commonly used for soldering purposes.

10.     ADVANTAGES AND DISADVANTAGES

ADVANTAGES

·         It is less costly.

·         It is more eco-friendly.

·         Air conditioners are big energy wasters that release harmful

chloro fluoro carbons into air. So instead we use cooling Fan.

·         The fan can be switched on and off with the help of a remote controller.

DISADVANTAGES

·         Low sensitivity

11.     APPLICATIONS

·         It is used in car engines.

·         It is widely used in medical field.

·         It is used in Industrial field.

·         It is used in ships.

·         It can also be used for domestic purposes.

12.  CONCLUSION

            We are proud to express our delight as the project we embarked upon is successfully finished within the target date. The project give as more confidence that we will be able to put in practice, whatever theoretical we gained during our course of study till now. If really persuades us to do more and more, perhaps in better way in future.

            Here a cooling fan will turn on when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a certain level.

            We take this opportunity to thank everyone once again who contributed directly or indirectly for successful completion of the project.

13.     FUTURE SCOPE

·         It can be used in GPS technology.

·         It can be used in VHF range in FM applications.

·         It can be further modified by replacing air conditioner instead of fan.

APPENDIX

3. BLOCK DIAGRAM DESCRIPTION

Here we are introducing a room temperature sensing system. Use of this system can control electronic devices like fan, ac, etc. LM35, a temperature sensing device which is made up of silicon material can sense temperature in the range of 0 to 100 degree Celsius. The device activates at room temperature.

The output of the sensor is connected to an optical display circuit. This display shows the present temperature of the room. Optical display circuit consists of the comparator LM324.It compares the input voltage from the temperature sensor circuit and the defined voltage. The temperature level is indicated through the LED display.

Whenever there is an increase in temperature, such that it reaches to a maximum level (user defined). The comparator output toggle to high and the output will switch on a time delay circuit. This is maintained for a particular period and the output of the time delay pass through an MOC. MOC is an optical isolator unit. It isolates ac circuit from dc circuit. The output of MOC is connected to gate circuit of the TRIAC and the output terminal is in series with load. Then whenever there is a decrease in room temperature, the circuit automatically switches off the TRIAC gate signal.

Another method for turning off the circuit is by using a humidity sensor and remote switch. A humidity sensor activates at room humidity level, sensed by LDR. Increment of humidity will cut off all circuit supply.

Next part is the IR remote. This circuit is used to turn on or off the system externally. When the IR rays are received, it is transmitted to the transistor through a diode. The transistor is turned on then the potential across the collector is very low and it acts as a negative trigger to the 555 timer. The timer produces a delay determined by the resistor andcapacitor. The output of 555 is applied to the flip flop and then connected to the transistor. From there it is connected to the optoisolator. The TRIAC of this IR unit is connected to the TRIAC of the fan drive circuit to turn on the system.

3.1 TEMPERATURE SENSOR CIRCUIT

LM 35

                                                               Fig: 1

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of ±¼°C at room temperature and ±¾°C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 µA from its supply, it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over a -55° to +150°C temperature range, while the LM35C is rated for a -40° to +110°C range (-10° with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.

FEATURES

·         Calibrated directly in ° Celsius (Centigrade)

·         Linear + 10.0 mV/°C scale factor

·         0.5°C accuracy guaranteed (at +25°C)

·         Rated for full -55° to +150°C range

·         Suitable for remote applications

·         Low cost due to wafer-level trimming

·         Operates from 4 to 30 volts

·         Less than 60 µA current drain

·         Low self-heating, 0.08°C in still air

·         Nonlinearity only ±¼°C typical

·         Low impedance output, 0.1 Ohm for 1 mA load

5.CIRCUIT DIAGRAM