The document describes an automatic street light circuit that uses a light dependent resistor (LDR) to sense light levels and control a relay that switches a light on and off. When it is dark, the resistance of the LDR increases, which causes a transistor to turn on and energize the relay, powering the light. During the day when it is light outside, the LDR's resistance decreases and the transistor turns off, cutting power to the light. Key components of the circuit include an LDR, transistors, a relay, resistors, and a battery power supply. The circuit can be used to automatically switch any light on at night and off during the day based on light level changes.

1. Submitted By:
Similendu Mallick
1521205148
Seminar
On
AUTOMATIC STREET
LIGHT

2. Content
 RELAY
 VOLTAGE REGULATOR
 FUSE
 LIGHT DEPENDENT RESISTOR
 RESISTOR
 TRANSISTOR
 BATTERY
 References

3. ABSTRACT
 A street light that automatically switches ON when the night falls and
turns OFF when the sun rises.
 In fact we can use this circuit for implementing any type of automatic
night light.
 The circuit uses a LDR to sense the light .
 When there is light the resistance of LDR will be low.
 So the voltage drop across POT R2 will be high.This keeps the
transistor Q1 ON. The collector of Q1(BC107) is coupled to base of
Q2(SL100).
 So Q2 will be OFF and so do the relay. The bulb will remain OFF.
 When night falls the resistance of LDR increases to make the voltage
across the POT R2 to decrease below 0.6V.
 This makes transistor Q1 OFF which in turn makes Q2 ON. The relay
will be energized and the bulb will glow.

4. BLOCK DIAGRAM

5.  Relay is an electromagnetic device which is used to isolate two circuits
electrically and connect them magnetically.
 They are very useful devices and allow one circuit to switch another
one while they are completely separate.
 They are often used to interface an electronic circuit (working at a low
voltage) to an electrical circuit which works at very high voltage.
 For example, a relay can make a 5V DC battery circuit to switch a 230V
AC mains circuit. Thus a small sensor circuit can drive, say, a fan or an
electric bulb.
 A relay switch can be divided into two parts: input and output.
Relay

6. VOLTAGE REGULATOR
 It is a voltage regulator (7805) integrated circuit. It is a member of
78xx series of fixed linear voltage regulator ICs. The voltage source in
a circuit may have fluctuations and would not give the fixed voltage
output.
 The voltage regulator IC maintains the output voltage at a constant
value. The xx in 78xx indicates the fixed output voltage it is designed to
provide. It provides +9V regulated power supply.
 Capacitors of suitable values can be connected at input and output pins
depending upon the respective voltage levels.

7. FUSE[1A]
 Fuse is an electronics safety device placed in a circuit consisting
of a replaceable plug or tube containing wire or metal that will
melt and break the circuit if the current exceeds a specified
amperage.
 Blow a fuse: to cause an electrical fuse to melt.

8. LIGHT DEPENDENT RESISTOR
 An LDR (Light dependent resistor), as its name suggests, offers
resistance in response to the ambient light.
 The resistance decreases as the intensity of incident light
increases, and vice versa.
 In the absence of light, LDR exhibits a resistance of the order of
mega-ohms which decreases to few hundred ohms in the
presence of light.
 It can act as a sensor, since a varying voltage drop can be
obtained in accordance with the varying light.
 It is made up of cadmium sulphide (CdS).
 An LDR has a zigzag cadmium sulphide track. It is a bilateral
device, i.e., conducts in both directions in same fashion.

9. RESISTOR
 Resistor is a passive component used to control current
in a circuit.
 Its resistance is given by the ratio of voltage applied
across its terminals to the current passing through it.
 Thus a particular value of resistor, for fixed voltage, limits
the current through it.
 They are omnipresent in electronic circuits.
 Resistors can be either fixed or variable.
 The low power resistors are comparatively smaller in size
than high power resistors.

10. TRANSISTOR
 BC107 is an NPN bi-polar junction transistor. A transistor, stands for
transfer of resistance, is commonly used to amplify current.
 A small current at its base controls a larger current at collector &
emitter terminals.
 BC107 is mainly used for amplification and switching purposes. It has a
maximum current gain of 800.
 The transistor terminals require a fixed DC voltage to operate in the
desired region of its characteristic curves. This is known as the biasing.
 The voltage divider is the commonly used biasing mode.
 For switching applications, transistor is biased so that it remains fully
on if there is a signal at its base.
 In the absence of base signal, it gets completely off.

11. TRANSISTOR[SL100]
 SL100 is a general purpose, medium power NPN transistor. It is mostly
used as switch in common emitter configuration.
 The transistor terminals require a fixed DC voltage to operate in the
desired region of its characteristic curves. This is known as the biasing.
 For switching applications, SL100 is biased in such a way that it
remains fully on if there is a signal at its base. In the absence of base
signal, it gets turned off completely.
 The emitter leg of SL100 is indicated by a protruding edge in the
transistor case. The base is nearest to the emitter while collector lies at
other extreme of the casing.

12. BATTERY
 It is a collection of one or more electrochemical cells in which stored
chemical energy is converted into electrical energy.
 One half cell houses the Anode to which the positive ions migrate from
the Electrolyte and the other houses the Cathode to which the
negative ones drift.
 The two cells are may be connected via a semi permeable
membranous structure allowing ions to flow but not the mixing of
electrolytes as in the case of most primary cells or in the same solution
as in secondary cells.
 The performance of the cell continues to dip gradually as the
concentration of ions in the solutions decrease, marked by an increase
in internal resistance eventually leading to the exhaustion of the battery.

13. References
 www.google.com
 www.wikipedia.com
 www.studymafia.org

14. Thanks