19-07-2012, 11:16 AM
HOUSE SECURITY SYSTEM
[attachment=28033]
Here is a low-cost, invisible laser
circuit to protect your house
from thieves or trespassers. A
laser pointer torch, which is easily available
in the market, can be used to operate
this device.
The block diagram of the unit shown
in Fig. 1 depicts the overall arrangement
for providing security to a house. A laser
torch powered by 3V power-supply is used
for generating a laser beam.
A combination of plain mirrors
M1 through M6 is used
to direct the laser beam
around the house to form a
net. The laser beam is directed
to finally fall on an
LDR that forms part of the
receiver unit as shown in Fig.
2. Any interruption of the
beam by a thief/
trespasser will result
into
energisation of
the alarm. The
3V power-supply
circuit is a conventional
fullwave
rectifier-filter
circuit. Any
alarm unit that
operates on 230V
AC can be connected
at the output.
The receiver unit comprises two identical
step-down transformers (X1 and X2),
two 6V relays (RL1 and RL2), an LDR, a
transistor, and a few other passive components.
When switches S1 and S2 are
activated, transformer X1, followed by a
full-wave rectifier and smoothing capacitor
C1, drives relay RL1 through the laser
switch.
The laser beam should be aimed continuously
on LDR. As long as the laser
beam falls on LDR, transistor T1 remains
forward biased and relay RL1 is thus in
energised condition. When a person
crosses the line of laser beam, relay RL1
turns off and transformer X2 gets
energised to provide a parallel path across
N/C contact and the pole of relay RL1.
In this condition, the laser beam will have
no effect on LDR and the alarm will continue
to operate as long as switch S2 is
on.
When the torch is switched on, the
pointed laser beam is reflected from a definite
point/place on the periphery of the
house. Making use of a set of properly
oriented mirrors one can form an invisible
net of laser rays as shown in the
block diagram. The final ray should fall
on LDR of the circuit.
Note. LDR should be kept in a long
pipe to protect it from other sources of
light, and its total distance from the
source may be kept limited to 500 metres.
The total cost of the circuit, including the
laser torch, is Rs 400 or less.
[attachment=28033]
Here is a low-cost, invisible laser
circuit to protect your house
from thieves or trespassers. A
laser pointer torch, which is easily available
in the market, can be used to operate
this device.
The block diagram of the unit shown
in Fig. 1 depicts the overall arrangement
for providing security to a house. A laser
torch powered by 3V power-supply is used
for generating a laser beam.
A combination of plain mirrors
M1 through M6 is used
to direct the laser beam
around the house to form a
net. The laser beam is directed
to finally fall on an
LDR that forms part of the
receiver unit as shown in Fig.
2. Any interruption of the
beam by a thief/
trespasser will result
into
energisation of
the alarm. The
3V power-supply
circuit is a conventional
fullwave
rectifier-filter
circuit. Any
alarm unit that
operates on 230V
AC can be connected
at the output.
The receiver unit comprises two identical
step-down transformers (X1 and X2),
two 6V relays (RL1 and RL2), an LDR, a
transistor, and a few other passive components.
When switches S1 and S2 are
activated, transformer X1, followed by a
full-wave rectifier and smoothing capacitor
C1, drives relay RL1 through the laser
switch.
The laser beam should be aimed continuously
on LDR. As long as the laser
beam falls on LDR, transistor T1 remains
forward biased and relay RL1 is thus in
energised condition. When a person
crosses the line of laser beam, relay RL1
turns off and transformer X2 gets
energised to provide a parallel path across
N/C contact and the pole of relay RL1.
In this condition, the laser beam will have
no effect on LDR and the alarm will continue
to operate as long as switch S2 is
on.
When the torch is switched on, the
pointed laser beam is reflected from a definite
point/place on the periphery of the
house. Making use of a set of properly
oriented mirrors one can form an invisible
net of laser rays as shown in the
block diagram. The final ray should fall
on LDR of the circuit.
Note. LDR should be kept in a long
pipe to protect it from other sources of
light, and its total distance from the
source may be kept limited to 500 metres.
The total cost of the circuit, including the
laser torch, is Rs 400 or less.