1. Automatic Temperature Control fan

2. TEMPERATURE CONTROL  Temperature control is a process in which change of temperature of a space is measured or otherwise detected, and the passage of heat energy into or out of the space is adjusted to achieve a desired average temperature.

3. PSU { Power Supply Unit }  A power supply is a device that supplies electric power to one or more electric loads.  Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source

4. PSU AS A TEMPERATURE CONTROLLER  The PSU powers all the computer's main components. Without a good, reliable PSU a computer cannot function properly, or it could damage the rest of the computer.  A PSU converts main AC to low-voltage regulated DC power for the internal components of a computer.  Sometimes a power supply unit can act as a part of cooling system because it has got an inbuilt fan.

5. DISADVANTAGE OF A PSU AS TEMPERATURE CONTROLLER  It is the most underrated part of a PC.  One might need a higher-rated PSU sometimes after further new installations.  Fans that are oversized for their serviced requirement in high flow noise thus increase stress on the fan and system.

6. WHY??????? Automated temperature control fan…………………

7. Objective:  Develop a product or hardware that can control the speed of the fan based on temperature  Conventionally used fans speed can be controlled by using the regulators which is the old and burdensome method. And this way of using becomes inefficient when the temperature has to be monitored over long time ranges  So a new method of automatic control of fan speed using the temperature sensors can be achieved  This method is innovative saves most of the time and energy  The principle behind this is very simple that is to turn on the fan when temperature is high and to turn off the fan when temperature is low this is achieved by using a thermistor which increases or decreases the resistance value.

8. Significance:  To monitor the environments that is not comfortable, or possible, for humans to monitor, especially for extended periods of time  Prevents waste of energy when it’s not hot enough for a fan to be needed.  To assist people who are disabled to adjust the fan speed automatically

9. CIRCUIT

10. DESCRIPTION:  This circuit can cool your heat generating electronic devices by operating a DC fan when the temperature in its vicinity increases above the preset level.  Its operation is fully automatic and turns off when the temperature returns normal.  It uses a small 12V DC brush fewer fans used in computer.

11.  The circuit exploits the property of Thermistor to operate the DC Fan. Thermistor is a kind of temperature dependent resistor and its resistance varies depending on the temperature in its vicinity. .Thermistor is bead like resistors available from 100 ohms to 10K or more values. Here a 4.7K NTC Thermistor is used. IC uA 741 is used as a voltage comparator to switch on the DC fan. Its INV input (pin2) gets an adjustable voltage through VR while its NON-INV (pin3) input gets voltage through a potential divider comprising R1 and the Thermistor. Thus the voltage at pin3 depends on the conductivity of the Thermistor.

12.  When the temperature is normal,pin3 gets higher voltage than pin2 and makes the output of IC high as indicated by Red LED. This high output keeps T1 off since its base is positive. DC fan remains off in this condition.  When temperature increases above the value set by VR, resistance of Thermistor decreases and the voltage at the pin3 decreases. As a result, output of IC becomes low to switch on T1. A small brush less DC fan (used in computers) turns on to increase the air circulation.  When the temperature returns normal, Fan automatically turns off. Diode D3 is necessary to remove back EMF when T1 turns off. Green LED indicates that the Fan is operating.

13. Voltage Regulation:  It’s basically this – maintain a precise voltage regardless of the current drawn by the load. Three basic components are needed to achieve good voltage regulation.  A precision reference (zener diode) to set the output voltage.  A muscle component (transistor) to deliver the required current.  An automatic controller (op amp) to adjust the transistor drive. The “prime directive” of the op amp is to adjust the base drive of Q1 delivering the required load current while keeping the output voltage at a fixed value.

14. Voltage regulator:  OUTPUT VOLTAGE Resistors RF1 and RF2 feed a fraction of the regulator output Vo to the op amp’s negative input V-. The op amp then adjusts the drive to Q1 such that V is equal to the zener voltage Vz. When this occurs, the output voltage is related to the zener voltage through the RF1, RF2 divider by Vo=Vz×(1+RF2/RF1)

15. Power Connections:  The power connections to the circuit is given from 230volts AC supply as the circuit works on DC current the process of conversion is achieved by full wave rectifier circuit.  Rectifier: A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other components.

16. Full Wave Rectifier:  A full-wave rectifier converts the whole of the input waveform to one of constant polarity as its output.  Full-wave rectification converts both polarities of the input waveform to DC, and is more efficient, However, In a circuit with a non- center tapped transformer, four diodes are required instead of the one needed for half-wave rectification. Four rectifiers are arranged this way are called a diode bridge or bridge rectifier.

17. full wave rectifier  For single-phase AC, if the transformer is center tapped, then two diodes back-to-back (i.e. anode- to-anode or cathode-to-cathode) form a full-wave rectifier (in this case, the voltage is half of that for the non-tapped bridge circuit above, and the diagram voltages are not to scale).

18. Working:  The working of the project is tested using various temperatures. Various temperature values are obtained by using 60W bulb and the result are tabulated for various when the voltage at the inverting terminal is high when compared to the voltage at the non inverting terminal the output will be as the temperature at non inverting terminal increase the output pin gradually increases and reaches a maximum value.

19. Output:  The output is noted and the result is tabulated as follows

20.  The sensitivity of the circuit is increased by varying the voltage level at pin 3  If the potential difference between the pi 2&3 is high then the sensitivity of the circuit is decreased. When the potential difference between pin 2&3 is less than the sensitivity of the circuit is increased greatly.  The circuit can also be used as a fire alarm in homes if the LED is replaced by a buzzer preceeded by an buzzer and power amplifier

21. Advantages:  Low installation cost.  Circuit is simpler in design.  The use of voltage regulators in fans can be avoided.  Power saving.  Temperature variations can be easily tracked down.  Less maintenance.  Easily repairable. Since there is no complex circuit setup involved.

22. Applications:  This circuit can be employed in places such as railway stations and such public places where people use to gather they don’t care about the working of these fans.  In such places these circuits can be employed so the voltage regulators need not be operated manually. Installing these circuits in such places leads to power saving as the circuit automatically adjusts the fans speed.  Another application of these circuits that this can be used in houses which uses air conditioners for power saving.

23. Result:  Automatic temperature controlled fan circuit was setup and connected to 230V mains supply and a 12volts output is obtained from full wave rectifier designed.  The required output is obtained according to different temperature conditions. The circuit was found to be working as the temperature increased, speed of the fan increased and vice versa.

24. Conclusion:  This circuit found to be more reliable than a regulator circuit since this seems to be more efficient than conventional regulator circuits. Since power consumption can be minimized a greater extent.  Even though it is simple this has a significant role to play in the development of technology. Every small step is significant in the path of success.  Our project though simple is significant in the current status of our country facing energy crisis.

25. Future Scope:  The project will concentrate on electric standing fan rather than other type of fan such as ceiling fan  The circuit can be expanded by incorporating a passive infrared sensor along with the temperature sensor. The passive infrared sensor can include a Frensel lens for sensing a 360° circumference beneath the fan can be turned on and off based on motion of persons approaching and leaving a selected area.  It can be also used as fire alarm and with sound to notify people that instrument is being over heated. This type of circuit as a fire alarm can also be used in electrical system where there is changes of fire and 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.

26. Bibliography: o http://www.redcircuits.com/ http://www.redcircuits.com/ o http://www.scrib.com/ http://www.scrib.com/ o http://www.allaboutcircuits.com/ http://www.allaboutcircuits.com/ o http://www.pc-control.co.uk/ http://www.pc-control.co.uk/ o http://www.howstuffworks.com/ o http://www.maxim-ic.com/an481/ o http://www.hardwaresecrets.com/ http://www.hardwaresecrets.com/

27. QUERIES?