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Make an Automatic Night Lamp using LDR and LM358 IC - KT863

Make an Automatic Night Lamp using LDR and LM358 IC - KT863


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  • Number of I/O Channels: 1
  • Type: Digital
  • Control signal: TTL level
  • Max. Allowable Voltage: 250VAC/110VDC
  • Max. Allowable Power Force: From C(800VAC/240W), From A(1200VA/300W)

LM358 IC

The pin diagram of LM358 IC comprises of 8 pins, where

  • Pin-1 and pin-8 are o/p of the comparator
  • Pin-2 and pin-6 are inverting i/ps
  • Pin-3 and pin-5 are non inverting i/ps
  • Pin-4 is GND terminal
  • Pin-8 is VCC+


  • Range of Single power supply is from 3V to 32V
  • Range of dual power supplies is from + or -1.5V to + or -16V
  • The supply current drain is very low, i.e., 500 μA
  • 2mV low i/p offset voltage
  • Common mode i/p voltage range comprises ground
  • It consists of two op-amps internally and frequency compensated for unity gain
  • The large voltage gain is 100 dB
  • Wide bandwidth is 1MHz
  • Range of wide power supplies includes single and dual power supplies


  • LM358 IC Connected to the Breadboard.
  • LM358 IC Pin No. 8 is connected to the positive supply and Pin No. 4 is GND.
  • LM358 Pin No. 2 connected to the middle leg of 10K Pot, 10K Pot 1st leg(left) connected to the positive supply and 10K Pot 2nd leg(right) is GND.
  • LM358 IC Pin No. 3 connected to the 22K resistor and resistor 2nd leg connected to the positive supply.
  • LM358 IC Pin No. 3 to connected LDR and LDR 2nd leg is GND.
  • 5 volt single channel relay module we connect on bread boardvcc to vcc ,gnd to gnd, input of relay module connect to the LM358 PIN NO 1 and we connect no & nc point of relay to ac 220volt.


Automatic night lamp as the name suggests is for turning ON and OFF the lamp automatically without the need of human interventions. It senses the light intensity from surroundings and find whether its day or night. And it automatically turns ON when the surrounding is dark and it turns OFF when it receives light from surroundings. A sensor called LDR is used to detect the light intensity.

The main part of this circuit is the light dependent resistor (LDR). It is a sensor which is a particular kind of resistor whose resistance decreases when exposed to light. Likewise it offers high resistance in dark. The resistance value changes from few 100 ohms to mega ohm range. The LDR is placed in a potential divider network. So voltage across LDR changes with intensity of light. Voltage across the LDR is given to the positive terminal of a comparator. Now a reference voltage is required to compare with the voltage across LDR. That reference voltage is made by using the pot or preset. So this preset can be used to adjust the sensitivity of the circuit. Next is the comparator made using LM358 op-amp which compares the voltage levels at its two inputs and gives output accordingly , If the voltage at positive terminal is greater, the output will be high and if the voltage at negative terminal is greater, the output will be low. That is if it is dark, resistance across LDR is high, so voltage drop across the LDR is high and voltage at positive terminal will be greater than the reference voltage. Therefore output of comparator will be high. The output of comparator is given to a transistor wired as a switch. Since enough voltage appears across the base emitter junction, the transistor conducts and current passes through the relay coils. So relay switches its contact and the bulb glows. Bulb is connected to the NO (Normally Open) pin of relay as it should be off when the relay coils are not energized. If the output of comparator is low, then transistor will be in OFF stage. So no current flows through the relay and bulb remains in OFF stage