Here is a circuit to control a fan according to the temperature of environment. If the temperature is high, then the fan will automatically turn on and if the temperature is low then the fan will automatically turn off.
The circuit uses following components
1. 9/12 volt power supply
2. LM741 op-amp
3. BC 547 transistor
4. 6.8 k resistor , 10 k resisotor
5. diode
6. fan or motor
Basic Principle
The circuit diagram is shown in the figure above. Take a breadboard and connect the components as shown above.
The potentiometer here provides the reference voltage to the comparator IC LM741 and which is used to adjust the sensitivity of the circuit by moving its wiper.
The circuits uses thermistor as a temperature sensor and is of negative temperature coefficient(NTC).
The thermistor and 6.8k resistor are arranged in series to make voltage divider configuration. So the voltage at thermistor will go to the pin 2 of the comparator ic.
The comparator IC LM741 will compare the voltage level of 2 inputs namely pin 3(+ve or non inverting input) and pin 2 (-ve or inverting input).
If the voltage level of 3 is greater than voltage level of 2 then the output at the pin 6 will appear high and that makes transistor saturated or on turning fan on.
If the voltage level of pin 3 is less than pin 2 then the output at the pin 6 will be low and the fan will be off.
The voltage from potentiometer is always kept constant after calibration.
WORKING OF CIRCUITS
CASE1=> when the temperature increases, the resistance of the thermistor will be decreased. So the voltage across it also decreases. So the pin 2 will get lower output than pin 3 which drives the transistor on and the fan will turn on.
CASE2=> when the temperature decreases, the resistance value of the thermistor will be increased. So the voltage across it will also be increased. So the pin 3 voltage is lower than Pin 2 voltage. So the output of the pin 6 will be low and the transistor will go to cutoff mode turning fan off.
THE DIODE IS USED ACROSS MOTOR IN REVERSED BIASED MODE TO REMOVE SPIKES AND NOISES FROM THE CIRCUITS.\
IF YOU FIND ANY DIFFICULTY PLEASE COMMENT............
The circuit uses following components
1. 9/12 volt power supply
2. LM741 op-amp
3. BC 547 transistor
4. 6.8 k resistor , 10 k resisotor
5. diode
6. fan or motor
Basic Principle
The circuit diagram is shown in the figure above. Take a breadboard and connect the components as shown above.
The potentiometer here provides the reference voltage to the comparator IC LM741 and which is used to adjust the sensitivity of the circuit by moving its wiper.
The circuits uses thermistor as a temperature sensor and is of negative temperature coefficient(NTC).
The thermistor and 6.8k resistor are arranged in series to make voltage divider configuration. So the voltage at thermistor will go to the pin 2 of the comparator ic.
The comparator IC LM741 will compare the voltage level of 2 inputs namely pin 3(+ve or non inverting input) and pin 2 (-ve or inverting input).
If the voltage level of 3 is greater than voltage level of 2 then the output at the pin 6 will appear high and that makes transistor saturated or on turning fan on.
If the voltage level of pin 3 is less than pin 2 then the output at the pin 6 will be low and the fan will be off.
The voltage from potentiometer is always kept constant after calibration.
WORKING OF CIRCUITS
CASE1=> when the temperature increases, the resistance of the thermistor will be decreased. So the voltage across it also decreases. So the pin 2 will get lower output than pin 3 which drives the transistor on and the fan will turn on.
CASE2=> when the temperature decreases, the resistance value of the thermistor will be increased. So the voltage across it will also be increased. So the pin 3 voltage is lower than Pin 2 voltage. So the output of the pin 6 will be low and the transistor will go to cutoff mode turning fan off.
THE DIODE IS USED ACROSS MOTOR IN REVERSED BIASED MODE TO REMOVE SPIKES AND NOISES FROM THE CIRCUITS.\
IF YOU FIND ANY DIFFICULTY PLEASE COMMENT............
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