PRESENTED BY:
M.KARTHIKEYAN
P.S.MOHAMMED MYDEEN

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AIM
Our aim is to design an “AUTOMATIC CONTROL OF STREET LIGHT” using LDR , and to implement it.
OBJECTIVES
1. To save the electric power.
2. To reduce the man power.
PRINCIPLE
It works under the principle , when the light falls on the LDR
depending upon the value of the resistance the light is turnedON and OFF.
ABSTRACT
• Needs no manual operation for switching.
• When there is a need of light it automatically detects that weather there is need of light or not.
• Light is switched OFF at night and ON at the morning hours.
LDR
• It is a special type of resistance whose value depends on the
brightness of light which is falling on it.
• It has resistance of about 1mega ohm when in total darkness,
but a resistance of only about 5k ohms when brightness illuminated.
• It responds to a large part of light spectrum.
TRANSFORMER
For 9v ac power supply we can use step down transformer in order to convert 230 volt to 9 volt.
P.C.B
• With the help of P.C.B it is easy to assemble circuit with neat and clean end products.
• P.C.B is made of Bakelite with surface pasted withcopper track-layout.

• Connection pin is passed through the hole and is soldered.
WORKING
• When light falls on the LDR then its resistance decreases which
results in increase of the voltage at pin 2 of the IC 555.
• IC 555 has got comparator inbuilt, which compares between
the input voltage from pin2 and 1/3rd of the power supply voltage
• When input falls below 1/3rd then output is set high otherwise
it is set low.
• Since in brightness, input voltage rises so we obtain no positive
voltage at output of pin 3 to drive relay or LED, besides in poor
light condition we get output to energize.