pls send the circuit diagram of this project at mohityd412[at]gmail.com

i have present you two circuit select best one from it ...



P1_____________22K Linear Potentiometer (See Notes)

R1_____________15K @ 20°C n.t.c. Thermistor (See Notes)
R2____________100K 1/4W Resistor
R3,R6__________10K 1/4W Resistors
R4,R5__________22K 1/4W Resistors
R7____________100R 1/4W Resistor
R8____________470R 1/4W Resistor
R9_____________33K 4W Resistor

C1_____________10nF 63V Polyester Capacitor

D1________BZX79C18 18V 500mW Zener Diode
D2_________TIC106D 400V 5A SCR
D3-D6_______1N4007 1000V 1A Diodes

Q1,Q2________BC327 45V 800mA PNP Transistors
Q3___________BC337 45V 800mA NPN Transistor

SK1__________Female Mains socket

PL1__________Male Mains plug & cable


The target device:

This circuit to adopt a fairly old design technique that aims to change the speed of a fan connected to the temperature minimum number of components and avoid the use of special purpose integrated circuits, often difficult to obtain.

Circuit operation:

R3, R4 and P1-R1 is connected to a Wheatstone bridge, where the R3-R4 produces a fixed supply of two thirds, "a reference to" the tension, and P1-R1 produces a heat-sensitive voltage "variable", and Q1 using the bridge balance indicator.

P1 is adjusted so that the "reference" and "variable" voltage is at a temperature just below the desired value of the timer, and under this condition Q1 Emitter and base voltages are equal and Q1 is turned off. When the temperature rises above that R1 "balance" of P1 R1 voltage falls below the "reference" value, so the first quarter are polarized, pulse charging C1.

This occurs because the entire circuit is powered by a 100 Hz half-wave voltage of the sector with the D3-D6 diode bridge without a smoothing capacitor and fixed to 18V with R9 and zener diode D1. Therefore 18V supply circuit is not true, DC, but rather a trapezoidal shape. C1, a pulse train of variable phase delay related to temperature and synchronous with the flow "zero voltage" point of each half cycle, producing a minimum of DDR SCR switching. Q2 and Q3 form a triggering device that generates a short pulse capable of driving the RCS.

Notes:

The circuit is designed for operation at 230 VAC. If your air conditioning system is about 115, you can change the value of R9 to 15K 2W. No other changes.

Circuit operation can be reversed, ie, to increase the fan speed when the temperature drops, simply as part of R1 and P1 positions. This approach is useful for controlling the flow of hot air, for example, using the heaters.

Thermistor value is not critical as I tried to 10K and 22K with good results.

In this circuit, if R1 and T1 are not mounted in the same environment, specific trigger points are subject to slight variations in temperature T1 changes due to temperature dependence of the characteristics of base-emitter junction. This tour is not suitable for use in precision applications, except for Q1 R1 and operate at temperatures equal.

Temperature / speed ratio increase can vary by changing the value of C1. The lower the value of C1 steep temperature / rate of increase in the ratio curve, and vice versa.

Attention! The circuit is connected to 230V, then some parts in the circuit is exposed to a potential deadly! Avoid touching the track when plugged and enclose it in a plastic box.

2.



Here is a simple circuit based on two transistors that can be used to control the speed of a 12 V DC fan depending on the temperature.A thermistor (R1) is used to sense the temperature. When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 more and so do the speed of the motor. Also, the brightness of the LED will be proportional to the speed of the motor.

Notes.

The R1 can be a 15K @ 20°C ,N.T.C thermistor.
The M1 can be a 12V,700mA fan motor.
The capacitor C1 must be rated 25V.
The circuit can be powered from a 12V PP3 battery or 12V DC power supply.
Assemble the circuit on a good quality PCB or common board

i need the circuit using 8051 microcontroller

to get information about the topic automatic temperature controlled fan circuit full report,ppt and related topic refer the page link bellow
http://studentbank.in/report-automatic-t...rolled-fan

http://studentbank.in/report-automatic-t...ull-report

http://studentbank.in/report-temperature...an-project

http://studentbank.in/report-fan-speed-control-circuit