This is automatic on/off street light control project based on 555 timer circuit. The street light on when there is darkness and gets off in day time. The circuit uses 4 LEDs for indication of bulb and for high power switching one can connect relay at the output.
Then it will be possible to turn ON/OFF any electrical appliances connected all the way through relay.
Circuit Principle of Automatic Street Light :
This circuit is based on timer IC 555. Pin 6 of IC 555 is connected as comparator with positive rail, the output at pin 3 goes high when the trigger pin 2 is at lower then 1/3rd level of the supply voltage. Conversely the output goes low (0) when it is above 1/3rd level. So small change in the voltage of pin-2 is enough to change the level of output (pin-3) from 1 to 0 and 0 to 1. The output has only two states high and low and cannot remain in any intermediate stage. It is powered by a 6V battery for portable use. The circuit is economic in power consumption. Pin 4, 6 and 8 is connected to the positive supply and pin 1 is grounded. To detect the present of an object we have used LDR and a source of light.
LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega 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. We have made a potential divider circuit with LDR and 100K variable resistance connected in series. We know that voltage is directly proportional to conductance so more voltage we will get from this divider when LDR is getting light and low voltage in darkness. This divided voltage is given to pin 2 of IC 555. Variable resistance is so adjusted that it crosses potential of 1/3rd in brightness and fall below 1/3rd in darkness.
Sensitiveness can be adjusted by this variable resistance. As soon as LDR gets dark the voltage of pin 2 drops 1/3rd of the supply voltage and pin 3 gets high and LED or buzzer which is connected to the output gets activated.
Parts of the Circuit:
9v Battery with strip
Switch
L.D.R (Light Depending Resistance)
I.C NE555 with Base
L.E.D (Light Emitting Diode) 3 to 6 pieces.
Variable Resistance of 47 KΩ
P.C.B (Printed Circuit Board of 555 or Vero board.
Components:
a) Battery: For 9v power supply we can use 6pcs dry cell or 6F22 9v single piece battery.
b)Switch: Any general purpose switch can be used. Switch is used as circuit breaker.
c) LDR: (Light Depending Resistance)
d) LED: (Light Emitting Diode)
e) Variable resistance: (Potentiometer)
f) PCB (Printed Circuit Board)
with the help of PCB it is easy to assemble circuit with neat and clean end products. P.C.B is made of Bakelite with surface pasted with copper track-layout. For each components leg, hole is made.
Connection pin is passed through the hole and is soldered.
How it Works?
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.
Guidelines
a) Use a Sensitive LDR. You can test it using a multimeter.
b) I.C should not be heated too much while soldering, excess heat can destroy it. For safety and easy to replace, use of I.C base is suggested. While placing the I.C pin no 1 should be made sure at right hole.
c) Opposite polarity of battery can destroy IC so please check the polarity before switching ON the circuit. One should use diode in series with switch for safety since diode allows flowing current in one direction only.
d) LED glows in forward bias only so incorrect polarity of L.E.D will not glow. Output voltage of our project is 7.3 volt therefore 4 LED in series can be easily used without resistance.
e) Each component should be soldered neat and clean. We should check for any dry soldered.
f) LDR should be so adjusted that it should not get light from streetlight itself.
