By
Alex
Meaden
-
-
This
circuit
is a
simple
wire
loop
alarm
that
can
be
used
in
doorways,
hallways,
or
any
other
place
the
tripwire
will
be
broken
by
intruders.
The
circuit
has
a
built
in
siren,
but
it
can
be
replaced
by a
relay
to
drive
an
external
siren,
commercial
alarm,
etc.
Schematic
Parts:
| Part |
Total Qty. |
Description |
Substitutions |
| R1 |
1 |
100K 1/2W 1% Resistor |
|
| R2, R4 |
2 |
10K 1/2W 1% Resistor |
|
| R3 |
1 |
1 Meg 1/2W 1% Resistor |
|
| C1, C3 |
2 |
0.1uF Ceramic Disc Capacitor |
|
| C2 |
1 |
0.01uF Ceramic Disc Capacitor |
|
| IC1 |
1 |
4001UBE Quad 2-i/p NOR Gate |
|
| Q1 |
1 |
MPSA14 Low Power NPN Transistor |
|
| SIREN |
1 |
Micro piezo siren 12V DC 150mA, 110dB @ 1M |
|
| LOOP |
1 |
See "Notes" |
|
| MISC |
1 |
Board, Wire, Socket For IC1 |
|
Notes:
1. The
loop can
be any
type of
hookup
wire,
with a
maximum
resistance
of about
90K.
Using
very
thin
wire
(40AWG,
for
example)
will
make a
very
sensitive
trip
wire,
but will
shorten
the
distance
it can
be
strung
due to
the high
resistance.
2. The
siren
can be
replaced
with a
relay to
drive
external
loads.
|
