Very sensitive
Uses timer IC 555
Item = Automatic Street
Light
India = Rs:230/ $5.10 USD
Other Country = $35.00 USD
1. Automatic street light (An introduction).
2. Principle
3. Component used
4. About the components.
a) 9V Battery
b) Switch
c) L.D.R
d) I.C 555
e) L.E.D
f) Variable Resistance
g) P.C.B
5. CIRCUIT DIAGRAM
6. WORKING
7. CONCLUSION
8. BIBLIOGRAPHY
An introduction
Automatic Street light needs no manual operation for switching ON and OFF when there is
need of light. It detects itself weather there is need for light or not. When darkness rises to a
certain value then automatically street light is switched ON and when there is other source of
light i.e. day time, the street light gets OFF. The sensitiveness of the street light can also be
adjusted. In our project we have used four L.E.D for indication of bulb but for high power
switching one can connect Relay (electromagnetic switch) at the output of pin 3 of I.C 555.
Then it will be possible to turn ON/OFF any electrical appliances connected all the way through
relay.
PRINCIPLE:
This circuit uses a popular timer I.C 555. I.C 555 is connected as comparator with pin-6
connected with positive rail, the output goes high(1) 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 can not 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 drops1/3rd of the supply voltage and pin 3 gets high and LED or buzzer which
is connected to the output gets activated.
Component used
1) 9v Battery with strip
2) Switch
3) L.D.R (Light Depending Resistance)
4) I.C NE555 with Base
5) L.E.D (Light Emitting Diode) 3 to 6 pieces.
6) Variable Resistance of 47 Kilo ohms
7) 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) L.D.R: (Light Depending Resistance) 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.
d) L.E.D: A diode is a component that only allows electricity to flow one way. It can be
thought as a sort of one way street for electrons. Because of this characteristic, dioded are
used to transform or rectify AC voltage into a DC voltage. Diodes have two connections, an
anode and a cathode. The cathode is the end on the schematic with the point of the triangle
pointing towards a line. In other words, the triangle points toward that cathode. The anode is,
of course, the opposite end. Current flows from the anode to the cathode. Light emitting
diodes, or LEDs, differ from regular diodes in that when a voltage is applied, they emit light.
This light can be red (most common), green, yellow, orange, blue (not very common), or infa
red. LEDs are used as indicators, transmitters, etc. Most likely, a LED will never burn out like a
regular lamp will and requires many times less current. Because LEDs act like regular diodes
and will form a short if connected between + and -, a current limiting resistor is used to prevent
that very thing. LEDs may or may not be drawn with the circle surrounding them.
e) Variable resistance: (Potentiometer) Resistors are one of the most common
electronic components. A resistor is a device that limits, or resists current. The current limiting
ability or resistance is measured in ohms, represented by the Greek symbol Omega. Variable
resistors (also called potentiometers or just "pots") are resistors that have a variable
resistance. You adjust the resistance by turning a shaft. This shaft moves a wiper across the
actual resistor element. By changing the amounts of resistor between the wiper connection and
the connection (s) to the resistor element, you can change the resistance. You will often see
the resistance of resistors written with K (kilohms) after the number value. This means that
there are that many thousands of ohms. For example, 1K is 1000 ohm, 2K is 2000 ohm, 3.3K is
3300 ohm, etc. You may also see the suffix M (mega ohms). This simply means million.
Resistors are also rated by their power handling capability. This is the amount of heat the
resistor can take before it is destroyed. The power capability is measured in W (watts).
Common wattages for variable resistors are 1/8W, 1/4W, 1/2W and 1W. Anything of a higher
wattage is referred to as a rheostat.
f) P.C.B: (Printed Circuit Board) 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 with copper
track-layout. For each components leg, hole is made. Connection pin is passed through the
hole and is soldered.
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.
Precautions:
a) LDR used should be sensitive. Before using in the circuit it should be tested with
multimeter.
b) I.C should not be heated much while soldering, too much heat can destroy the I.C. 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 I.C 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) L.E.D glows in forward bias only so incorrect polarity of L.E.D will not glow. Out put
voltage of our project is 7.3 volt therefore 3 LED in series can be easily used with out
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.