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Alarm Circuits Page
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Alarms: #-C
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Last Updated on:
Monday, October 03, 2011 06:07 PM |
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Circuits Designed by Dave Johnson, P.E. |
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Bad Light Bulb Indicator
This request came from a Discover Circuits visitor. He wanted to turn on a LED
indicator light whenever a circuit detected a burned out tail/brake light on a car
or truck. The circuit shown below uses a transistor switch, to detect current
flowing through a low value resistor. If current is flowing to a light bulb,
the circuit shunts current around a LED light, keeping the LED turned off. If there
is no current detected, the LED turns on. The circuit should operate from 6v
to 24v....
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Chain Link Fence Alarm
Long stretches of steel fence can be monitored using the simple circuit below. An
insulated wire is woven through the links in the fence. Where the fence begins, the
circuit is connected to an earth ground and the security wire. At the end of the
fence, the wire is connected to one of the steel posts, held in the ground.
The typical earth ground resistance will be in the 1000s of ohms range,...
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Cut Phone Line Alarm
Burglars, rapists and other criminals will
often cut a phone line before they break into a home. The cut phone line will
prevent many alarm systems from alerting the police. The battery powered
circuit below will sound an alarm when the unit no longer detects the voltage
present on an active phone line....
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| Links to electronic circuits,
electronic schematics, designs for engineers, hobbyists, students & inventors:
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12 Volt Alarm Power Supply - A 12 Volt power supplied designed for Ron's Modular
Burglar Alarm. However, being a popular supply voltage this circuit will have many other
uses as well….(circuit / schematic design added 6/06) |
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120 VAC Low Voltage Alarm - This circuit will activate a beeper alarm whenever
the AC line voltage is less than 100vac. [Designed by David A. Johnson] |
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2 Zone Intruder Alarm - This is a two-zone alarm - with automatic exit, entry
and siren cut-off timers. It can be triggered by the usual types of normally-closed input
devices - such as magnetic reed contacts - foil tape - PIRs etc. I've used a 12-volt
supply in the diagram - but the circuit will work at anything from 9 to 15-volts. All you
need do is select a siren, buzzer and relay to suit the voltage you want to use....
[Circuit designed by Ron J.] |
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2-input alarm - This article describes a 2-Input alarm developed on the PIC
LICK-1 Module using a Microchip PIC16F628-04. The program uses the internal 4MHz
oscillator and if any other frequency is used, the timer values will need to be
changed....(electronic circuit added 05/06/07) |
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3 Zone Duress Alarm - This is a 3 zone alarm for use in high risk areas or
possible duress situations. Typical examples being banking or betting booths. The alarm
consists of 3 normally open push button switches which can be hidden or in plain view.
Once pressed the alarm will latch and a LED will light showing which zone has pressed the
alarm... [Circuit by Andy Collison] |
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4 Digit Keypad - (diagram added 6/03) |
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4 in 1 Burglar Alarm - In this circuit, the alarm will be switched on under the
following four different conditions: 1. When light falls on LDR1 (at the entry to the
premises). 2. When light falling on LDR2 is obstructed. 3. When door switches are opened
or a wire is broken. 4. When a handle is touched. The light dependent resistor LDR1 should
be placed in darkness near the door lock or handle etc. If an intruder flashes his
torch.... [Radioland.nt.au] |
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4-Digit Alarm Control Keypad - This Keypad is suitable for the Modular Burglar
Alarm. However, it has other applications. Pressing a single key will energize the relay.
Entering the Four-Digit code of your choice will de-energize it. (Circuit design
added 08/08/08) |
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5 Zone Alarm Circuit - (electronic schematic added 8/02) |
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555-Timer Based Motorcycle Alarm - This circuit features an intermittent siren
output and automatic reset. It can be operated manually using a key-switch or a hidden
switch; but it can also be wired to set itself automatically when you turn-off the
ignition. By adding external relays you can immobilize the bike, flash the lights etc.
(Circuit design added 08/08/08) |
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5-Digit Alarm Control Keypad - This Keypad is suitable for the Modular Burglar
Alarm. However, it has other applications. Entering the First Four Digits of your chosen
Five-Digit code, will energize the relay. Entering the Full Five-Digit code, will
de-energize it. (Circuit design added 08/08/08) |
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6 Zone Alarm with 7 Segment Display - This alarm system has 6 independent zones,
1 timed entry/exit zone, a 7 segment LED display and a test or walkthrough facility.
Suitable for a small office or home environment, it can also be adapted to use a
combination lock or keypad to set and reset the alarm.... [Andy Collison, designer] |
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A 4-Digit Alarm Control Keypad - This Keypad is suitable for the Modular Burglar
Alarm. However, it has other applications. Pressing a single key will energize the relay.
Entering the Four-Digit code of your choice will de-energize it…. [Designer Ron J.] |
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A 4-Digit Keypad Controlled Switch - This is a Universal version of the
Four-Digit Alarm Control Keypad. I have modified the design to free up the relay contacts.
This allows the circuit to operate as a general-purpose switch. I've used a SPCO/SPDT
relay, but you can use a multi-pole relay if you wish....(electronic schematic added
05/09) [Designer Ron J.] |
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A 555 -Timer Based Motorcycle Alarm - This circuit features an intermittent
siren output and automatic reset. It can be operated manually using a key-switch or a
hidden switch; but it can also be wired to set itself automatically when you turn-off the
ignition. By adding external relays you can immobilize the bike, flash the lights etc.
(Circuit design added 08/08/08) [Circuit Designed by Ron J.] |
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A 5-Digit Alarm Control Keypad - This Keypad is suitable for the Modular Burglar
Alarm. However, it has other applications. Entering the First Four Digits of your chosen
Five-Digit code, will energize the relay. Entering the Full Five-Digit code, will
de-energize it. (Circuit design added 08/08/08) [Circuit Designed by Ron J.] |
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A Battery-Powered One-Time-Only Burglar Alarm - This is a single zone alarm,
with independently adjustable Exit, Entry and Siren Cut-Off timers. When the alarm is
activated its Siren will sound once, for up to 20-minutes. Then it will switch off and
remain off. If you wish, you can use a mains power supply. But the extremely low standby
current makes battery power a realistic option.... [Ron J.'s design] |
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A CMOS 4060 Burglar Alarm - This is a single zone alarm, with automatic exit,
entry and siren cut-off timers. It will accommodate all the usual types of normally-closed
input devices, such as magnetic reed contacts, foil tape, PIRs etc. But it's easy to add a
normally-open trigger.... [Design by Ron J.] |
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A CMOS Based Motorcycle Alarm - This circuit features an intermittent siren
output and automatic reset. It can be operated manually using a key-switch or a hidden
switch; but it can also be wired to set itself automatically when you turn-off the
ignition.… [Design by Ron J.] |
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A CMOS Based Single Zone Alarm - This circuit features automatic Exit and Entry
delays, timed bell cut-off, and system reset. It has provision for normally-open and
normally-closed switches, and will suit all of the usual input devices (Pressure Mats,
Magnetic Reed contacts, Foil Tape, PIRs and Inertia-Sensors, see.... [Design by Ron J.] |
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A Dozen Small CMOS Alarm Circuits - This is a selection of small self-contained
alarm circuits. They have a very low standby current; and are suitable for battery
operation. Some are triggered by normally-open and normally-closed switches. Some react to
changes in light or temperature. The result is a variety of output times and patterns.....
[Circuit designer is Ron J.] |
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A One-Time-Only Burglar Alarm - This alarm is designed to sound its Siren only
once. That is - when the alarm is activated - the Siren will sound for a preset length of
time. Then it will switch off and remain off. The alarm will not re-activate.
[Circuit designer is Ron J.] |
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A Shed / Garage Alarm - This is a basic single-zone burglar alarm circuit. Its
features include automatic Exit and Entry delays. It has an extremely small standby
current. This makes it ideal for battery-powered operation. Use it in your caravan,
mobile home, lock-up, or anywhere mains power is not available.... [Circuit by Ron J.] |
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A simple electronic buzzer - This very simple circuit just uses a couple of
resistors, a capacitor and the easily available 555 timer IC. The 555 is setup as an
astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise
when switched on. The frequency can be changed by varying the 10K resistor.... [Radioland.nt.au] |
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A Simple Fire-Door Alarm - This circuit will let you know when something that
should be kept closed, has in fact been left open. Attach it to a Fire-Door. It will allow
you to pass through the door as usual. However, if it's left open for more than 30-seconds
or so, the buzzer will sound.... [Circuit by Ron J.] |
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A Simple Shop-Door Alarm - Attach this circuit to the door of an unattended
shop, or reception area, and the sound of the buzzer will tell you when you have a
customer. Add a siren, and it becomes a simple intruder alarm…. [Design by Ron J.] |
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A Simple Transistor Based Motorcycle Alarm - This is an even simpler transistor
based motorcycle alarm. The circuit features a timed output and automatic reset. It can be
operated manually using a key-switch or a hidden switch. By adding an external relay, it
will set itself automatically, and/or immobilize the machine, every time you turn-off the
ignition. It's easily adapted for a 6-volt system, so it will protect your "Classic
Bike"... [Design by Ron J.] |
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A Simpler CMOS Single Zone Alarm - This circuit features automatic Exit/Entry
delays, timed Bell Cut-off and System Reset. It will accommodate the usual normally-closed
input devices (Magnetic Reed contacts, Micro Switches, Foil Tape and PIRs). And, with a
simple modification, a normally-open trigger may be added... [Design by Ron J.] |
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A Transistor Based Burglar Alarm - This is a simple transistor-based burglar
alarm circuit. Its features include automatic Exit and Entry delays - together with a
timed Bell cut-off and Reset. It's designed to be used with the usual types of
normally-closed input devices such as - magnetic-reed contacts - micro switches - foil
tape - and PIRs....(circuit added 01/2010) [Circuit Designed by Ron J.] |
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A Transistor Based Motorcycle Alarm - This circuit features a timed output and
automatic reset. It can be operated manually using a key-switch or a hidden switch. By
adding an external relay, it will set itself automatically, and/or immobilize the machine,
every time you turn-off the ignition. It's easily adapted for a 6-volt system, so it will
protect your "Classic Bike"... [Circuit Designed by Ron J.] |
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AC Line Under/Over Voltage Alarm - Power lines, which deviate much beyond normal
voltages can damage expensive electronic equipment. The circuit below sounds an
alarm whenever the line voltage is higher or lower than normal. I set the alarm
limits at about +-15% from standard levels. The circuit rectifies and filters the
power line signal. I set the resistor values, so the DC voltage produced is close to
1% of the RMS value of the line. Thus, a 120vac line would yield about 1.2v DC.
That voltage is fed to a pair of voltage comparators. The outputs of the comparators
decide if the sampled voltage is above, below or acceptable.... [Designed by David A.
Johnson] |
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Alarm Circuit - Surround your Entire Yard with this Laser Alarm ….(Circuit
design added 12/08) |
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Alarm control keypad - The IC is a quad 2 input "AND" gate, a CMOS 4081. These
gates only produce a HIGH output, when BOTH the inputs are HIGH. When the key wired to 'E'
is pressed, current through R1 and D1 switchs Q5 on.The relay energises; and Q5 is
'latched on' by R8. Thus, the Alarm is set by pressing a single key,say one of the two
non-numeric symbols.... [Ron J.'s circuit |
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Alarm monitors rotational speed of DC-mmotor - 2-Oct-08 Issue of EDN This Design
Idea monitors the rotating speed of a dc fan motor, sounding an alarm and powering down if
the motor stalls.... [Design Idea by Peter Demchenko, Vilnius, Lithuania] |
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Alarm Power Supply - ….(Circuit design added 03/08) |
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Alarm Power Supply With Battery Back-up - This Power Supply is suitable for the
Modular Burglar Alarm. However, it has other applications. It is designed to provide an
output of 12-volts, with a current of up to 1-amp. In the event of mains failure, the
back-up battery takes over automatically....(Circuit design added 08/08/08) |
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Alarm PSU - A 12 Volt power suppiled designed for Ron's Modular Burglar Alarm.
However, being a popular supply voltage this circuit will have many other uses as
well….(circuit / schematic design added 6/06) |
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Alarm System - (design added 8/03) |
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Alarm tells you to close the refrigerator door - 25-Jun-09 Issue of EDN A
simple gadget that you place inside the refrigerator alerts you by beeping if the door
stays open for 20 seconds or longer.... [Design Idea by Boris Khaykin, TRW Automotive,
Livonia, MI] |
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American Police Car Siren (linscott) - Scroll down to locate this circuit. The
555 on the right is wired as an alarm tone generator and the second 555 timer on the left
is wired as a low frequency astable timer which generates a ramp waveform of about 6
seconds that is buffered by the transistor and again used to frequency modulate the tone
generator. The transistor is used to help strengthen the signal to the
speaker....(electronic design added 08/08/08) |
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An Enhanced Shed / Garage Alarm - This is an enhanced version of the simple
Garage/Shed Alarm. The Entry and Exit delays have been increased to about 30-seconds, and
I've added a timed Siren cut-off and automatic Reset. I've also replaced the LED with an
entry Buzzer. These enhancements mean that the new version will have a much wider
application.... [Circuit by Ron J.] |
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An Expandable Multi-Zone Modular Burglar Alarm - This circuit features automatic
Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed
and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. By using the
Expansion Modules, you can add as many zones as you require; some or all of which may be
the inertia (shock) sensor type... [Circuit designed by Ron J.] |
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An Expandable SCR Based Burglar Alarm - This is a simple SCR based burglar alarm
circuit. Its features include automatic Exit and Entry delays, together with a timed Bell
Cut-off and Reset. The basic alarm has a single zone. This will be adequate in many
situations. However, the modular design means that you can add as many zones as you like
to the system. Details of a Four-Zone expansion module are provided.... [Ron J.'s circuit] |
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An Expandable Transistor Based Burglar Alarm - This transistor based alarm
features automatic Exit and Entry delays, together with a timed Bell Cut-off and system
Reset. Along with the Exit/Entry zone, the basic alarm board has one Instant Zone.
This will be adequate in many situations. However, the modular design means that it's easy
to add as many zones as you like to the system. Details of a Four-Zone expansion module
are provided.... [Ron J.'s circuit] |
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An SCR Based Burglar Alarm - (electronic design added 6/07) |
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Anit Theft Motorcycle Alarm - (schematic added 9/02) |
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Audio Security Monitor - A remote listening circuit. The area to be monitored is
connected via a cable and allows remote audio listening….. [designer Andy Collison] |
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Auto Burglar Alarm (Randy Linscott) - This alarm circuit is based on two 555
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.…. |
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Automatic Intruder Alarm - Circuit designed by Ron J (electronic design added
6/07) |
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Automatic Night Lamp with Morning Alarm - (electronic Circuit / Schematic added
10/04) |
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Battery Low Voltage Beeper - This circuit provides an audible and visual low
voltage warning for 12V battery powered devices. Idle current: 6ma Low Voltage Warning
current: 15ma…. [G. Forrest Cook] |
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Battery Powered One Time Alarm Only (Ron J) - This is a single zone alarm - with
independently adjustable Exit, Entry and Siren Cut-Off timers. It will accommodate the
usual types of normally-closed input devices - such as magnetic-reed contacts, foil tape
and PIRs…. [Ron J.'s design] |
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Battery-Powered One-Time-Only Burglar Alarm - This is a single zone alarm, with
independently adjustable Exit, Entry and Siren Cut-Off timers. When the alarm is activated
its Siren will sound once, for up to 20-minutes. Then it will switch off and remain off.
If you wish, you can use a mains power supply. But the extremely low standby current makes
battery power a realistic option. |
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Beeper - [Radioland.nt.au] |
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Beeper bug transmitter for fox hunt & vehicle tracking - (diagram added 05/07)
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Big Ben Sound - This circuit produces famous Big Ben sound. It produces
"ding dong" sound when switched ON. Basically circuit alternates between two
frequencies which are adjustable. This produces "ding-dong" sound. The first C
(left) oscillates at about 1Hz. The second IC's tone is modulated by changing
voltage at output of first IC.... (added 10/05) [Radioland.nt.au] |
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Brakelight Flasher - This is basically a flasher circuit modified to turn on and
off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator.
The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying
preset VR1. The ON time of circuit is given by: TON= 0.69xC1x(R1 + VR1) second
and OFF time is: TOFF= 0.69xC1xVR1 second.... [Radioland.nt.au] |
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British Police Car Siren - The first circuit simulates the siren of a British
police car. It uses two 555 timers in the circuit. The 555 on the right is wired as an
alarm tone generator and the second 555 timer on the left is a 1 Hz astable multivibrater....(electronic
design added 08/08/08) |
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Broken Charger-Connection Alert - Detects if a device is not properly connected
to its supply. Suitable for battery chargers, portable appliance supplies etc.
(added 3/050 |
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Burglar Alarm - This is a single zone alarm, with automatic exit, entry and
siren cut-off timers. It will accommodate all the usual types of normally-closed input
devices, such as magnetic reed contacts, foil tape, PIRs etc. But it's easy....(electronic
design added 7/08) |
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Car Alarm - (application / block diagram added 6/07) |
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Car Alarm and Immobilizer - This circuit features automatic exit and entry
delays - an optional instant alarm zone - an optional intermittent siren output - and an
automatic reset. By adding external relays you can immobilize the vehicle and flash the
lights…. [Design by Ron J.] |
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Car Alarm Sound Booster - For car alarms, emphasis should be put on hearing the
audible alert and identifying it as belonging to your ‘wheels’. Unfortunately, modern car
alarm systems seem to have the more or less the same alarm sound — especially if they are
from the same brand. Also….must register on this site... [Published in Elecktor
July/August 2010] |
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Car anti theft wireless alarm - This FM radio-controlled antift alarm can be
used with any vehicle having 6to 12-volt DC supply system. The mini VHF, FM transmitter is
fitted in vehicle at night when it is parked in car porch or car park. The
receiver unit with CXA1019, a single IC-based FM radio module, which is freely available
in market at reasonable rate, is kept inside. Receiver is.... [Radioland.nt.au] |
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Car Back-up Alarm - The brake lights of automobile trigger this circuit on
and off. This save annoyance of alarm when it is not needed. This is an older
circuit which was published in Popular Electronics Magazine, but still a good circuit
today. (Tony van Roon's electronic design added 6/06) [Tony van Roon's circuit] |
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Car HiJack Alarm - Before fitting this or any other engine cut-out to your
vehicle, carefully consider both the safety implications of its possible failure, and the
legal consequences of installing a device that could cause an accident. If you decide to
proceed, you will need to use the highest standards of materials and
workmanship....(electronic design added 6/07) |
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Car indicator alarm - Schematic only, no circuit description |
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Car-Police Siren - This siren circuit simulates police, fire or other emergency
sirens that produce an up and down wail. (Circuit design added 08/08) |
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Chain Link Fence Alarm - Long stretches of steel fence can be monitored using
the simple circuit below. An insulated wire is woven through the links in the fence.
Where the fence begins, the circuit is connected to an earth ground and the security
wire. At the end of the fence, the wire is connected to one of the steel posts, held in
the ground. The typical earth ground resistance will be in the 1000s of ohms range,
which is low enough to keep the n-channel FET turned off in the circuit below. If
the wire is cut or broken,.... [Designed by David A. Johnson] |
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Cheap Bicycle Alarm - The author wanted a very cheap and simple alarm for some
of his possessions, such as his electrically assisted bicycle. This alarm is based on a
cheap window alarm, which has a time-switch added to it with a 1-minute time-out. The
output pulse of the 555 replaces the reed switch in the window alarm.….must register on
this site... [Published in Elecktor July/August 2010] |
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CMOS 4017 Sequential Timer - This circuit uses a Cmos 4017 decade counter to
create a sequence of four separate events. The number of events in the sequence may be
increased to nine or ten. And the length of each event is controlled independently. D13
causes the sequence to repeat continuously. If you leave out D13, the sequence will run
only once. I've used a 12-volt supply in the diagram, but the circuit will work at
anything from 5 to 15-volts.... [Circuit design by Ron J.] |
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CMOS 4060 Alarm - This is a single zone alarm - with automatic exit, entry and
siren cut-off timers. It will accommodate all the usual types of normally-closed input
devices - such as magnetic-reed contacts - foil tape - PIRs etc…. [Circuit design by Ron
J.] |
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CMOS 4060 Burglar Alarm - This is a single zone alarm, with automatic exit,
entry and siren cut-off timers. It will accommodate all the usual types of normally-closed
input devices, such as magnetic reed contacts, foil tape, PIRs etc. But it's easy to add a
normally-open trigger....(Circuit design added 06/07/08) |
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CMOS Based Motorcycle Alarm - This circuit features an intermittent siren output
and automatic reset. It can be operated manually using a key-switch or a hidden switch;
but it can also be wired to set itself automatically when you turn-off the
ignition....[Ron J.'s circuit] |
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CMOS Based Vehicle Anti-Theft Alarm - This car alarm circuit features Exit and
Entry delays, an instant alarm zone, an intermittent siren output and automatic Reset. By
adding external relays you can immobilize the vehicle and flash the lights….(Circuit
design added 06/07/08) |
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CMOS Single Zone Alarm - (diagram added 6/03) |
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Cold Activated Switch - The thermistor used has a resistance of 15k at 25
degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the
Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of
temperatures. A slight amount of hysteresis is provided by inclusion of the 270k resistor.
This prevents relay chatter when temperature is near the switching threshold of this
circuit.... [Andy Collison's circuit] |
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Combination Digital Lock - A multiple input combination loack using CMOS counter
IC's. Flexibility and code change is allowed by changing output connections…. [Circuit
designed by Andy Collison] |
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Combination Lock PIC16F84 - (diagram added 6/03) |
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Controller provides multiple alarm-driver formats - 15-Jan-98 Issue of EDN
Using a piezoelectric element for alarm applications offers low cost, low power, and
flexibility. By coupling this element with a 12C508 programmable controller (Microchip
Technology, Chandler, AZ], you can implement an eight-pin alarm generator. This
approach provides multiple driver formats with a minimum of additional cost and footprin....
[Design Idea by William Grill, Riverhead Systems, Littleton, CO] |
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Countersurveillance Monitor - This simple-to-build, yet effective circuit can
help you search out and remove electronic eavesdropping devices…. [Tony van Roon's
circuit] |
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Cut Phone Line Detector - A while ago I got an email asking for the schematic of
a circuit to detect cut phone lines. It didn't take me long to find this circuit in
Electronics Now. When the circuit detects that a phone line has been cut, it activates a
MOSFET which can be used to drive a relay, motor, etc. It can also be connected to a
security system... [Arron Cake] |
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Cut Phone Line Detector - This circuit speaks for itself. When the phone
line is okay, Q1 acts as a short with a very high ohms value via R1, R2, and R3 for a
total of about 66 MegOhm so very high. When the phone line is cut (Tony van Roon's open),
it activates the MosFet (Tony van Roon's Q3) via transistor Q2 to drive the load.
Substitutes are fine, none of the components are critical.... [Tony van Roon's circuit] |
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Alarms:
#-C
D-G
H-O
P-R
S
T-U
V-Z
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