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Alarm Circuits
Alarms:  #'s       A - C       D - G       H - L       M - Q       R - T      
U - Z

 

Last Updated: December 07, 2017 02:03 PM

 

Circuits Designed by Dave Johnson, P.E.

Door Knob 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. . . Circuit by David Johnson P.E.-May, 2000

Doorbell heard in Basement -  If you can't hear your doorbell when you are in your basement try this circuit.  This circuit takes advantage of the 24vac power source located near the furnace.  Using a simple current transformer technique, the circuit sounds a beeper whenever the . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

 

Electric Field Disturbance Monitor-Alarm Discriminator + Battery Monitor -  This schematic is the alarm discriminator plus the batterry monitor of my "Electric Field Disturbance Monitor".  The system can detect human and animal motion by the electric fields they disturb. . . Circuit by David A. Johnson P.E.-March, 2002

Fence Alarm  -  It was deer hunting season and cattle rancher was fed up with hunters cutting his barbed wire fence, to gain entrance onto his property.  The rancher want to be alerted when the barbed wire was cut.  The circuits below is placed inside a small plastic box which is placed inside the house.  A power jack for the +12v input and a terminal block for the earth ground and sensor wire connections are installed.  Two additional terminals were connected to a siren.  Central to the design is a closed pushbutton switch.  When pressed, the button would test the circuit by simulating a broken fence wire. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 2 Oct 2009

Front End + Power Supply Circuits of the Electric Filed Disturbance Monitor -  This schematic is the power supply and front-end sections of my field monitor, "Electric Field Disturbance Monitor".  The system can detect human and animal motion by the electric fields they disturb . . . Hobby Circuit designed by David A. Johnson P.E.-March, 2002

 
Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Factory Siren -  This circuit produces a sound similar to a factory siren.  It makes use of a 555 timer IC used as an astable multivibrator of a center frequency of about 300Hz.  The frequency is controlled by the pin 5 of the IC.  When the supply is switched ON, the capacitor charges slowly and this alters the voltage at pin 5 of the IC hence __ Designed by Radioland.nt.au

Fake Alarm Blinker -  Get an old used alarm panel with keypad, remove the standard internal electronic board, add this circuit and a 3.6V lipo battery.  Push one button for blink, and another button for off.  This way you fool stupid people to think you got a real alarm unit installed, so they go some where else and brake in. __ Designed by Thomas Scherrer OZ2CPU

Fake Car Alarm Light -  Whenever the carís ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system. . . Circuit by David Johnson P.E.-October, 2005

Fake LED Alarm Simulator -  This circuit simulates an alarm to discourage thieves and it is originally designed to be used on bicycles but can be used for cars too.  It blinks a LED on and off thus simulating a real alarm circuit.  The fake LED alarm electronic circuit consists of a square wave oscillator generating a 1 MHz signal with a pulse width of 10 __ Designed by Popescu Marian

Faulty Car Indicator Alarm -  Before taking a turn, either left or right, car drivers need to switch on the carís turn-indicator lamps so that the approaching vehicle drivers can take precaution accordingly.  An accident is __ Electronics Projects for You

Fence Alarm  -  It was deer hunting season and cattle rancher was fed up with hunters cutting his barbed wire fence, to gain entrance onto his property.  The rancher want to be alerted when the barbed wire was cut.  The circuits below is placed inside a small plastic box which is placed inside the house.  A power jack for the +12v input and a terminal block for the earth ground and sensor wire connections are installed.  Two additional terminals were connected to a siren.  Central to the design is a closed pushbutton switch.  When pressed, the button would test the circuit by simulating a broken fence wire. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 2 Oct 2009

Fire Alarm -  With the onset of summer, chances of fire accidents increase.  Such fire accidents can be prevented if timely alarms are available.  The circuit presented here warns the user against such fire __ Electronics Projects for You

Fire Alarm -  In this fire alarm circuit project, a thermistor works as the heat sensor.  When temperature increases, its resistance decreases, and vice versa.  At normal temperature, the resistance of the thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature ncreases beyond 100įC.  The circuit uses __ Designed by Popescu Marian

Fire Alarm -  This circuit warns the user against fire accidents.  It relies on the smoke that is produced in the event of a fire.  When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR decreases.  This causes the resistance of LDR to increase and the voltage at the base of the transistor __ Designed by Radioland.nt.au

Fire Alarm using Thermistor -  In this fire alarm circuit, a thermistor works as the heat sensor.  When temperature increases, its resistance decreases, and vice versa.  At normal temperature, the resistance of the thermistor (TH1) is __ Electronics Projects for You

Fire Alarm using Thermistor -  In this fire alarm circuit, a Thermistor works as the heat sensor.  When temperature increases, its resistance decreases, and vice versa.  At normal temperature, the resistance of the Thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature increases beyond 100 C.  The circuit uses readily available components and can be easily constructed on any general-purpose PCB. __ Learning Electronics

Fire Alarm with a Thermistor -  This project can effectively be used as a temperature-sensing fire alarm.  Here, an NTC thermistor is used as the temperature sensor.  Resistance of the NTC thermistor decreases with an increase in __ Electronics Projects for You

Fire-Door Alarm -  Battery-Powered Alarm Circuits:  This circuit will let you know when something that should be kept closedhas in fact been left open.  If you attach it to say a Fire-Doorit will allow you to pass back and forth freely.  It's only when the door is open for more than about 30-secondsthat the buzzer will sound the alarm.  The Page includes a free SiMetrixcircuit simulation. __ Designed by Ron J.

Five Zone Alarm -  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. __ Designed by Andy Collinson

Five-Digit Alarm Control KeypA - D -  Alarm Control Keypads:  This Keypad is suitable for the Modular Burglar Alarm.  However, it has other applications.  Entering the First Four Digits of your chosen Five-Digit codewill energize the relay.  Entering the Full Five-Digit codewill de-energize it. __ Designed by Ron J.

Five-Digit Alarm KeypA - D -  This is an enhanced 5 digit keypad which may be used with the Modular Alarm System.  This switch will suit the Modular Burglar Alarm circuit.  However, it also has other applications.  The Keypad must be the kind with a common terminal and a separate connection for each key.  On a 12-key pad, look for 13 terminals.  The matrix type with 7 terminals will NOT do.  Choose the five keys __ Designed by Andy Collison

Five-Zone Alarm SystE - M -  Alarms and security related electronic circuit diagrams / circuit schematics __ Designed by Andy Collison

Flashing Light to simulate Car Alarm -  Whenever the carís ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system . . . Hobby Circuit designed by David Johnson P.E.-October, 2005

Footstep Alarm for Human Traffic -  This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps.  At has an adjustable sensitivity . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Four Digit KeypA - D -  This is an enhanced 4 digit keypad which may be used with the Modular Alarm System __ Designed by Ron J.

Four Small Transistor Alarm Circuits -  Battery-Powered Alarm Circuits:  This is a selection of simple self-contained transistor based alarm circuitscomplete with photographs.  They are designed around the Complementary Latch.  All may be triggered by both normally-open and normally-closed switches.  They have a very low standby currentand are ideal for battery operation. __ Designed by Ron J.

Four-Digit Alarm Control KeypA - D -  Alarm Control Keypads:  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. __ Designed by Ron J.

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Alarms:  #'s       A - C       D - G       H - L       M -Q       R - T       U - Z


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