Along with the modernization, people are more prone to the comfort zone. Several inventions have been made to meet this requirement. Following the same trend, here we have presented a simple circuit; automatic light operated switch using LDR and IC741. People are really busy, every second has vital role in our busy schedule.
Why shall we waste our valuable time turning on every switch in the building? The situation turns more troublesome when one needs to reach the ground floor just because it’s getting dark and s/he needs to turn on the light. The importance of this circuit; automatic light operated switch is much felt in such traumatic situations.
Who will stay calm being victimized when the solution is right in front of us? To overcome such problems, you don’t need to throw hefty sum of your hard-earned money. What you need to do is just connect the electric appliances you want to operate automatically with the circuit of automatic light operated switch. Then the switch will automatically turn on, LDR will serve its purpose and you will get your surrounding lightened without pressing the switch.
Circuit description of automatic light operated switch using LDR and IC741
The circuit presented here is light operated circuit using LDR. LDR is a semiconductor component whose value of resistance is changed according to the intensity of light falling on it i.e. more the light falls on the LDR, the less the resistance is and vice-versa.
The heart of the circuit is very common operation amplifier IC 741(IC1) and is used here in inverting mode. The LDR is used here as light sensor and variable resistor; VR1 is used to adjust the sensitivity of LDR. Capacitor C1 behaves as a feedback capacitor. The output from pin number 6 of IC1 (IC 741)is given to the base of transistor T1 through resistor R5,which is used here as relay driver circuit. Diode D1 is used as protector and protect relay from surge current. The load to be controlled is connected to the output pin of relay.
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Resistor (all ¼-watt, ± 5% Carbon)
R1 = 1 KΩ
R2 = 1KΩ, ½ W
R3 = 10 KΩ, ½ W
R4 = 10 KΩ
R5 = 2.2 KΩ, ½W
R6 = 330 Ω, 1/2W
VR1 = 470 KΩ
C1 = 0.1 µF/30V
IC1 = 741
T1 = SL100 or BC148B
D1 = OQ79
RL1 = 400 Ω, 9V realy
SW1 = Double Pole Double Through (DPDT)