Simple Circuit Temperature Controlled DC Fan

Here is a Simple Circuit Temperature Controlled DC Fan primarily based on 2 transistors which will be used to control the speed of a 12 V DC fan looking on the temperature.A thermistor (R1) is employed to sense the temperature. When the temperature will increase the base current of Q1 (BC 547) will increase that in flip 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 lot of and so do the speed of the motor. Also, the brightness of the LED are going to 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.

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Remote controlled appliance switch circuit

Description.
Here is a versatile remote controlled appliance switch that can ON or OFF any appliance connected to it using a TV remote.

 IR remote sensor IC TSOP 1738 is used for recieving the signal.
Normally when no signal is falling on IC3 the output of it will be
high.This makes Q1 OFF.When a signal of 38 KHz from the TV remote falls
on the IC3 its output goes low.This makes Q1 conduct and a negative
pulse is obtained at pin 2 of IC 1  NE 555.Due to this IC1 wired as a
monostable multivibrator produces a 4 Sec  long high signal at its out
put.This high out put is the clock for IC 2 which is wired as a Flipflop
and of , its two outputs pin 3 goes low and pin 2 goes high.The high
output at pin 2 is amplified to drive the relay .For the next signal 
the outputs of IC2 toggles state. Result, we get a relay toggling on
each press on the remote.Any appliance connected to this circuit can be
switched ON or OFF.
Circuit Diagram with Parts List .
Notes.

• Before
  wiring the circuit make sure that the carrier frequency  of the TV
  remote you have is 38 KHz.For that wire the sensor part only ,point
  your remote to the TSOP1738 and press any switch.If  out put of
  TSOP1738  goes  low them ok, your remote is of 38Khz type.Nothing to
  worry almost all TV remote are of this type.
• You can use any
  switch because for any switch the code only changes,the carrier
  frequency remains same.We need this carrier frequency only.
• Assemble the circuit on a good quality PCB or common board.
• The appliance can be connected through NO or NC  and contacts of the relay .

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