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This
is a
complete
alarm
system
with 5
independent
zones
suitable
for a
small
office
or home
environment.
It uses
just 3
CMOS
IC's
and
features
a timed
entry /
exit
zone, 4
immediate
zones
and a
panic
button.
There
are
indicators
for each
zone a
"system
armed"
indicator.
The
schematic
is as
follows:
To
watch
circuit
clearly
Right
click on
circuit
and
choose
"save
picture
as" to
save on
your PC.
Please
Note:
This
diagram
is drawn
with
Relay
and
Switch
Contacts
labeled
click
here
Switch
and
Relay
Wheres
the
Parts
List ?
On the
diagram
click
here for
more
info.
Circuit
Notes:
Each
zone
uses a
normally
closed
contact.
These
can be
micro
switches
or
standard
alarm
contacts
(usually
reed
switches).
Suitable
switches
can be
bought
from
alarm
shops
and
concealed
in door
frames,
or
window
ledges.
Zone 1
is a
timed
zone
which
must be
used as
the
entry
and exit
point of
the
building.
Zones 2
- 5 are
immediate
zones,
which
will
trigger
the
alarm
with no
delay.
Some RF
immunity
is
provided
for long
wiring
runs by
the
input
capacitors,
C1-C5.
C7 and
R14 also
form a
transient
suppresser.
The key
switch
acts as
the
Set/Unset
and
Reset
switch.
For good
security
this
should
be the
metal
type
with a
key.
Operation:
At
switch
on, C6
will
charge
via R11,
this
acts as
the exit
delay
and is
set to
around
30
seconds.
This can
be
altered
by
varying
either
C6 or
R11.
Once the
timing
period
has
elapsed,
LED6
will
light,
meaning
the
system
is
armed.
LED6 may
be
mounted
externally
(at the
bell box
for
example)
and
provides
visual
indication
that the
system
has set.
Once set
any
contact
that
opens
will
trigger
the
alarm,
including
Zone 1.
To
prevent
triggering
the
alarm on
entry to
the
building,
the
concealed
re-entry
switch
must be
operated.
This
will
discharge
C6 and
start
the
entry
timer.
The
re-entry
switch
could be
a
concealed
reed
switch,
located
anywhere
in a
door
frame,
but
invisible
to the
eye. The
panic
switch,
when
pressed,
will
trigger
the
alarm
when
set.
Relay
contacts
RLA1
provide
the
latch,
RLA2
operate
the
siren or
buzzer. |
