fig :- Pinout of LM741
The above diagram show the pin configuration of the comparator IC
LM741.
fig;- The internal diagram of LM741
The LM741 has two inputs:-
i> Inverting terminal(marked with negative sign)
ii> Non-inverting terminal(marked with positive sign)
One of the pins out of the two is applied with a fixed reference voltage while the other pin is fed with the voltage whose level needs to be monitored.
The monitoring of the voltage is done with reference to the fixed voltage that's been applied to the other complementary pin.
Therefore if the voltage which is to be monitored goes above or falls below the fixed reference threshold voltage, the output reverts state or changes
its original condition or changes its output voltage polarity
In this project, we will go over how to build an automatic night
light circuit in which an LED will turn on when it becomes dark using an LM741 op amp chip as a comparator.
As soon as there is ambient darkness sensed by the circuit, it will automatically turn on an LED, which will stay on as long as it is dark.
The component that allows for this light sensing is a LDR.
The LDR detects light levels and its resistance changes based on the amount of light it picks up.
We can exploit this varying resistance that the LDR gives off to know whether there is darkness in the surroundings or whether it is bright.
fig:- circuit diagram
So the positive pin is connected to the + 6V (say) and the negative pin is connected to the ground. When the LDR is exposed to darkness ,large amount of voltage from power supply get allocated to the LDR. Thus the voltage in non inverting is greater than the non-inverting terminal.There fore the output is high(up to VCC) so, LED connected to the output terminal will be power ON.
When the LDR is exposed to the light ,the resistance of LDR drops significantly which leads to drop the voltage.Thus,the non-inverting terminal have greater voltage than the inverting terminal. The output will be low but it may contain the voltage greater than 0.7V so,the voltage divider is made which divides the output voltage which transistor remain in off condition so the led will not glow.