Automatic Street Light Using IC555 and LDR


•This is a simple circuit that is useful to conserve
electricity at day time.

•Many a times we find street lights glowing during the day and hence there is a lot of electricity wastage, this can be minimized by the help of this circuit which automatically turns it off.

•This takes a 12V ac input. A step down transformer is used that converts 230V AC to 12V AC.





•VR1-1 Meg

•LDR- 10 mm LDR





•IC1- NE555


•D1 to D5- 1N4007

•12V relay and

•PCB(printed circuit board)

About IC555:

•This is a small ic
with 8 pins. Contrary to its normal use as an astable or monostable multivibrator the ic works as a comparator in this circuit. It is necessary to note that the operation of a 555 is as follows; the output goes high upon the receipt of a trigger , pulse on input , pin2.


• The output of ne555 goes high upon the receipt of a
trigger pulse on the input, pin2. This pulse is a voltage whose level is lower than 1/3 of the supply voltage. The output goes low again when the voltage at second input, pin6, has briefly exceeded 2/3 of the supply level.

•. In the present design, the second input is not used, but the output of the chip cannot revert to low state, since pin 6 is connected directly to positive supply rail.

•In principle the supply voltage for the circuit must equal the coil voltage of the relay. Do not apply more than 16V however, this may damage the IC555. The current consumption of the circuit is 4mA, exclusive of the relay, at a supplied level of 12V. The sensitivity of the trigger circuit can be controlled by 1 Meg preset.

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    3 Discussions


    Question 11 months ago

    How we connect the pole of relay in the circuit?