AUTOMATIC ROOM LAMP

AUTOMATIC
ROOM LAMP

ABSTRACT:



This simple circuit
can be used as an automatic
room lamp
controller. It disables the
room lamp
at daytime and enables it at night. The circuit is built around a light
-
dependant resistor (LDR1),
reed switch (S1), two transistors BC547 (T1) and SK100 (T2), a 12V 1
-
change over (C/O) relay
(RL1), a step
-
down transformer X1 (12V
-
0
-
12V, 250mA se
condary) along
with some discrete
components.



During daytime, lamp operation is not necessary due to the presence of sunlight so LDR1

is
used. Fit LDR1 near the
room window where it can receive sunlight (reflected sunlight is
enough). At day
time if you o
pen the
room door, resistance of LDR1 reduces and keeps both
transistors T1 and T2 in cut
-
off s
tate. Relay RL1 does not energiz
e and lamp remains off.



At night, if you open the
room door, resistance of LDR1 is high, which keeps both the transistors
T1 an
d T2 in con
ducting state. Relay RL1 energiz
es and lamp (B1) is switched on. The power
supply required to operate the circuit is derived from transformer X1.







CIRCUIT DIAGRAM:









POWER SUPPLY
:
















LDR

CIRCUIT


TRANSISTOR


LAMP


RELAY


TRANSFOR
MER


BRIDGE
CIRCUIT



FILTER


REGUALATOR



The input to the circuit is applied from the regulated power supply. The a.c. input i.e.,
230V from the mains supply is step down by the transformer to 12V and is fed to a
rectifier. The
output obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c voltage,
the output voltage from the rectifier is fed to a filter to remove any a.c components present even
after rectification. Now, this voltage i
s given to a voltage regulator to obtain a pure constant dc
voltage.

ADVANTAGES:



No unnecessary usage of
man
power



It is operated 5v DC.

APPLICATIONS:



Homes



Schools, colleges



Hospitals



Shopping complex