MICRO POWER
OVER-TEMPERATURE
ALARM
The circuit
is powered for
years by a
single 3 volt
lithium battery.
It sounds an
alarm when the
temperature
exceeds a
certain point.
With some minor
changes the
circuit could
also be
configured for
an under
temperature
(freeze) alarm.
The circuit uses
a cheap but
accurate
thermistor as
the temperature
sensor.
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POWER REMINDER
BEEPER
This circuit
produces a short
beep once each
minute. It is
powered directly
off the 120vac
power line to
remind you that
a device
connected to the
circuit is
turned on. It is
simple enough to
be packaged
inside a small
plastic box. It
might be ideal
for computers,
printers or some
test equipment
that shouldn't
be left on all
night. |
MACHINE POWER
LOSS BEEPER
For some
medical
equipment it is
important for an
operator when
power is lost to
the machine. The
beeper is
powered from a
9v battery and
requires the
machine to have
a power switch
with a third set
of contacts. |
DOORKNOB ALARM
Many
companies offer
simple alarm
devices for
personal use in
bedrooms or
hotel rooms. A
metal chain
attached to a
box holding the
electronics is
placed around
the inside
doorknob of a
wood door.
Anyone grabbing
the knob from
the outside is
detected by the
electrical
capacitance
change that
occurs from the
human hand
contact between
the knob and the
box. Almost all
of the
commercial
devices sold use
a more expensive
and power
consuming radio
frequency
circuit approach
to detect the
capacitance
change. But, a
very inexpensive
and micro power
technique can
also work. This
circuit
schematic should
dramatically
reduce the cost
of the device
and allows it to
operate for many
years from one
set of
batteries.
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WATER SEEPAGE
ALARM
This simple
circuit sounds a
beeper when its
electrodes
detect water. It
is powered by a
single 1.5v N
cell. A small
1.5v button
battery will
also work. |
ELECTRIC FIELD
DISTURBANCE
MONITOR
This
schematic is the
power supply and
front-end
sections of the
field monitor
that is
discussed in
more detail at
Electric
Field
Disturbance
Monitor.
(this link
is off-site)
The system can
detect human and
animal motion by
the electric
fields they
disturb. |
ELECTRIC FIELD
DISTURBANCE
MONITOR
This
schematic is the
motion
discriminator
alarm and
battery monitor
sections of the
field monitor
that is
discussed in
more detail a
Electric
Field
Disturbance
Monitor.
(this link
is off-site)
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TIME TO DUST
INDICATOR
I thought about
this circuit
when I heard
that a lot
cleaning
personal in
hotels were
either dusting
rooms more often
than necessary
or not enough. I
have not yet
built and tested
this circuit
completely but
in concept it
should work. The
circuit draws
very low current
from a +3v
battery and
could be housed
in a package
similar to a
small ashtray.
The assembly
might be placed
in a suitable
out of the way
area to collect
dust. It would
alert a maid
when it was time
to dust the
room. The
circuit detects
dust with an
infrared LED
that is pulsed
so its light
shines onto a
smooth flat
plate. Any dust
settling onto
the surface is
detected by a
phototransistor,
mounted at a 90
degree angle
from the LED.
When the dust
reaches a
particular
level,
sufficient light
is reflected
into the
phototransistor
to change the
logic state of
the circuit to
an alarm
condition. The
alarm output
could be
connected to a
beeper, a
flashing LED or
to one of the
LED flashing
circuits in this
Tutorials circuit
section. |
UNPLUGGED POWER
CORD ALARM
Many medical
devices, such a
portable X-ray
and ultrasound
equipment, carry
their own
batteries.
However, the
frantic pace of
some hospital
emergency rooms
might cause the
device to be
shoved off into
a corner without
being plugged
back into an AC
power source to
recharge their
batteries. So, I
designed this
circuit to emit
an audible alarm
whenever the
device’s power
cord was
unplugged from
the wall for a
period of time.
The device was
designed to snap
onto the outside
of a power cord,
where it senses
the AC electric
field emitted.
No direct
connection to
the internal
wires of the
power cord is
needed. I also
included a low
battery voltage
monitor. |
12C508
Smart
Lock:
The base
sends a
data
sequence
(the
password)
which is
recognized
by the
key. The
key
checks
the
sequence
and -if
it
recognizes
it
-sends
to the
base
another
data
sequence,
as an
answer
to the
password.
At the
Time
when the
base
gets a
correct
answer
(which
means
that the
key has
been
introduced),
the
relay is
put into
action,
and it
can
command
a number
of
consumers.
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4 Digit
Keypad:
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5 Zone
Alarm
Circuit:
|
5 Zone
Alarm
Circuit:
|
Active
IR
Motion
Detector:
|
Alarm
Control
keypad:
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Alarm
Loop
Sensor
(LM3915):
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Alarm
Touched
Triggered:
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Almost
Ultrasonic
Motion
Sensor:
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Anit
Theft
Motorcycle
Alarm:
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Anti
Theft
Security
for Car
Audios:
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Auto
Burglar
Alarm:
This
alarm
circuit
is based
on
two555
Timers.
The
alarm
will
sound
your car
horn if
anyone
opens
the car
door
while
the
circuit
is
armed.
The
Timers
will
allow
you to
leave
the car
without
sounding
the
horn. To
turn the
circuit
on S1
must be
closed.
To set
the
alarm,
open S2
( it is
normally
closed )
this
will
give you
about5
seconds
to get
out and
close
the
door.
The exit
delay
Time is
set by
R1 and
C1. If
anyone
opens
the
doors
for more
then two
seconds
the horn
will
sound
until
power is
removed
from the
circuit.
The2
second
Time is
set by
R2 and
C2. If
you open
the
door,
you must
deactivate
the
alarm by
closing
S2. This
very
basic
circuit
could be
used for
a home
also.
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Automatic
Entry
Control
System:
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Automotive
Alarm
System:
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Basic RF
Transmitter
for PIR
Sensors:
|
Battery
Low
Voltage
Alarm #2:
|
Battery
Low
Voltage
Alarm:
|
Battery
Low
Voltage
Beeper:
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Capacitance
Proximity
Alarm:
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Car
Burglar
Alarm:
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Car
indicator
alarm:
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CMOS
Single
Zone
Alarm:
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Cold
Activated
Switch:
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Combination
Lock
(PIC16F84):
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Combination
Lock
(Simple
Version):
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Combination
Lock:
This
circuit
is very
basic to
build.
To open
a the
lock
which is
connected
to the
K1 Load.
you must
press
each
momentary
switch
in the
correct
sequence.
The
sequence
used in
this
circuit
is
S1,S2,S3,S4.
If any
of the
other
switches
are
pressed
the
circuit
will
reset
and you
will
need to
start
over.
Depending
on how
you wire
the
switches,
you can
use any4
switch
combination
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Cut
Phone
Line
Detector
#1:
Can be
used to
alarm
security
system
|
Cut
Phone
Line
Detector
#1:
Can be
used to
alarm
security
system
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Digital
Combination
Lock:
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Digital
Entry
Lock:
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Dummy
alarm:
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Electronic
Card
Lock
System:
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Electronic
Door
Codelock:
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Electronic
Lock:
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Enhanced
Alarm
Keypad:
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Four
Digit
Keypad:
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Freezer
Door
Alarm:
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Frost
Alarm:
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Fuse
Monitor
/ Alarm:
a simple
way to
see if a
fuse has
blown
without
removing
it from
its
holder
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Gate
Alarm
Circuit:
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Glitch
Detector:
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Home
Security
Project:
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Infrared
Alarm:
This
circuits
consist
of two
parts,
the
first
part
will
transmit
a
signal,
and the
second
part
will
detect
that
signal
and
trigger
a relay.
To
adjust
the
circuit,
hold
down S1
while
pointing
LED1 at
the
receiver.
Adjust
R6 until
you hear
the
relay
click.
You can
increase
range by
using a
high
output
LED for
LED1.
Bright
light
will
stop the
receiver
from
responding
to the
transmitter.
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Infrared
Transmitter
/
Detector:
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Intruder
Radio
Alert
System:
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Knock
Alarm:
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Loop
Alarm:
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Low
Power
RFID
Transponder:
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Luggage
Security
System:
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