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

 

Last Updated: November 21, 2017 05:44 AM

 

Circuits Designed by Dave Johnson, P.E.

Under/Over Voltage Alarm on AC Line   -  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 . . . Circuit by David A. Johnson P.E.-March 29, 2009

Unplugged Appliance Alarm   -  I received a call from an administrator at a large prison.  He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens in a commons area.  He wanted a battery-powered device, which could be mount . . . Circuit by Dave Johnson P.E.-April 25, 2010

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 . . . Circuit by Dave Johnson P.E.-July 08, 2000

Water Cistern Level Alarm   -  I received an unusual request from a Discover Circuits visitor a while back.    The guy had a deep water cistern which has to be filled when nearly empty.  The cistern was described as a deep cylindrical tube, holding 1000s of gallons of drinking water.    Periodically, the cistern is filled from a tanker truck, when the water inside reached a critical level.    The guy wanted a simple circuit he could build which would flash an LED when the water level reached a certain depth.    That flasher would tell him it was time to order more water . . . Circuit by David Johnson P.E.-April 27, 2014

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 . . . Hobby Circuit designed by David A. Johnson P.E.-June 11, 2000

Wire Loop Security Alarm   -  A wire is looped through various objects which are to be monitored.  The loop wire is typically an aircraft cable but could also be any insulated stranded wire.  The loop is attached to a table or desk.  Should the loop be cut, the alarm is sounded . . . Hobby Circuit designed by David A. Johnson P.E.-July 09, 2006


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

UHF Doppler Motion Detector -  Schematic only __ Designed by va3iul

UHF Movement Detector -  Schematic only __ Designed by va3iul

Ultrasonic Beam Barrier -  This circuit generates inaudible ultrasound to make a barrier across the entry.  At the moment the circuit detects a break in the sound barrier, it generates a loud alarm indicating the entry of a person.  This can be used to protects the entry passages and helps to detect unauthorized entry of persons in protected areas.  The __ Designed by D Mohankumar

Ultrasonic Intruder Detector -  The next circuit is an ultrasonic intruder detector. It uses Doppler shift from a moving object. Ultrasonics aren't used much for this commercially as they can be a bit temperamental to set up and tend to detect cats and curtains moving in a draft. Modern detectors tend to use a narrow beam microwave system which only scans a small area such as a doorway. Ultrasonics tend to scan the whole room. __ Designed by Richard Torrens

Ultrasonic Proximity Detector -  We the humans can hear sound of up to 20kHz frequency only. This proximity detector works at a frequency of 40 kHz. It uses two specially made ultrasonic transducers: One transducer __ Electronics Projects for You

Ultrasonic Proximity Detector 2 -  This ultrasonic proximity detector comprising independent, battery-powered transmitter and receiver sections makes use of a pair of matched ultrasonic piezoceramic transducers operating at around 40 kHz each.  This circuit can be __ Electronics Projects for You

Ultrasonic radar alarm -  The objective of this project is to use inexpensive PIR sensor to detect if a human has moved.  To build this project I use a PIC18F25K20 microcontroller to detect if the sensor had change state and it will emit a sound from the speaker or piezo, the MCU also detect the voltage of the battery in the startup, the algorithm it´s very simple it use an interrupt on change to detect the change on the PIR sensor. __ Designed by Helio Pereira

Ultrasonic Radar Alarm -  Schematic only __ Designed by va3iul

Ultrasonic Sound Beam Burglar Alarm -  This unique burglar alarm makes use of the invisible, inaudible ultrasonic sound beam to detect movements.  Ultrasonic transducers operate at maximum efficiency when driven at 40kHz frequency.  So an ultrasonic transmitter __ Electronics Projects for You

UM3561 Siren Generator Design -  UM3561 is an excellent ROM IC that can generate Multi siren tones simulating Police siren, Ambulance siren, Fire brigade siren and Machine gun sound.  This 8 pin low power IC can work down to 2.4 volts.  The UM 3561 is a low cost siren generator designed for use in toy applications.  The IC has an inbuilt oscillator and tone __ Designed by D Mohankumar

Under/Over Voltage Alarm on AC Line -  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. . . Circuit by David A. Johnson P.E.-March, 2009

Unplugged Appliance Alarm -  I received a call from an administrator at a large prison.  He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens in a commons area.  He wanted a battery-powered device, which could be mount. . . Circuit by Dave Johnson P.E.-April, 2010

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. . . Circuit by Dave Johnson P.E.-July, 2000

USB Based Temperature Monitor using the ADuC7120 Precision Analog Microcontroller & an External Thermistor  -  Circuit linearization techniques can be accomplished in software; however, that will not be discussed here.  , Despite the powerful ARM7 core and high speed SAR ADCs, the ADuC7122 still provides a low power solution __ Analog Devices from the Lab

Using the MAXQ3210 in a Light-Beam Alarm SystE - M -  App Note 4153  -- 2/26/2008 --  (add 5/08) __ Maxim Integrated

Vehicle Anti-Hijack Alarm No.3 -  Automobile Alarm Circuits:  Like the first two Hijack Alarmsif a door is opened while the ignition is switched onthe circuit will trip.  And after a few minutes delaywhen the thief is at a safe distancethe Siren will sound.  But this time the engine does not go on to fail automatically.  Insteadit will continue to run until the thief turns off the ignition.  Then the engine will not re-start. __ Designed by Ron J.

Versatile Audio-Visual Alarm -  This circuit uses an NE555 timer IC, some LEDs, a couple of piezo buzzers and a few other components to produce audio-visual effects as per your requirement.  The timer NE555 and __ Electronics Projects for You

Volumetric Sensor Alarm -  Detects small variations in air pressure;  Can be battery powered (6/12V) __ Contact: Flavio Dellepiane, fladello @ tin.it

Wailing Siren -  This circuit provides a warbling sound to any alarm circuit.  IC2 is wired as a low frequency astable with a cycle period of about 6 seconds.  The slowly varying ramp waveform at C1 is fed to PNP emitter follower Q1, and is then used to frequency modulate alarm generator IC1 via R6.  IC1 has a natural center frequency of about 800Hz. __ Designed by Tony van Roon  VA3AVR

Warble Alarm -  The circuit above provides a 'warble' alarm-call generator that simulates the european 'dee-dah-dee-dah' type sirens used in several european countries __ Designed by Tony van Roon  VA3AVR

Warning Alarm with CD4 001 -  Unorthodox warning alarm circuit presented here is infact a single chip based general purpose sounder, which produces a pulsed alert tone when its input receives a valid trigger signal.  The circuit can be easily interfaced with a number of electronic gadgets and sensors and it requires only 12V dc supply input for proper __ Designed by T.K. Hareendran

Water Activated Alarm -  The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C.  Under dry conditions, the transistor will have no bias current and be fully off.  As the probes get wet, a small current flows between base and emitter and the transistor switches on.  A larger current flows in the collector circuit enabling the 555 osillator to sound __ Designed by Tom 

Water Alarm -  The LM1830 fluid detector IC from National Semiconductor is designed to be able to detect the presence of fluids using a probe.  This chip requires a relatively high supply voltage and is not the most frugal power consumer.  It is also quite specialised so unless you are buying in bulk the one-off price is not cheapmust register on this site __ Designed by Elecktor July/Aug, 2010

Water Cistern Level Alarm -  I received an unusual request from a Discover Circuits visitor a while back.    The guy had a deep water cistern which has to be filled when nearly empty.  The cistern was described as a deep cylindrical tube, holding 1000s of gallons of drinking water.    Periodically, the cistern is filled from a tanker truck, when the water inside reached a critical level.    The guy wanted a simple circuit he could build which would flash an LED when the water level reached a certain depth.    That flasher would tell him it was time to order more water. . . Circuit by David Johnson P.E.-April, 2014

Water Level Alarm -  A circuit that offers visual indication of fluid level in a vessel, with a switchable audible alarm.  Example uses would be to monitor the level of water in a bath or cold storage tank. __ Designed by Andy Collison

Water Level Alert -  This circuit will emit an intermittent beep (or will flash a LED) when the water contained into a recipient has reached the desired level.  It should be mounted on top of the recipient (e.g.  a plastic tank) by means of two crocodile clips, acting also as probes. __ Red Free Circuits

Water Level Indicator with Alarm -  Here is a simple, versatile circuit which indicates the level of water in a tank.  This circuit produces alarm when water level is below the lowest level L1 and also when __ Electronics Projects for You

Water Level Indicator with alarm -  This circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full.    The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs.  When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch __ Designed by Radioland.nt.au

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 . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Water Sensor Alarm -  This small water sensor alarm circuit makes a loud warning sound when a humidity sensor detects a quantity of water.  This circuit assembly is an application of low power comparator LM1801 made by National Semiconductor.  The reference voltage for the integrated circuit is fixed with the help of R2.  When pin 4 of the LM1801 __ Designed by Popescu Marian

Water-level Alert -  This circuit will emit an intermittent beep (or will flash a LED) when the water contained into a recipient has reached the desired level.  It should be mounted on top of the recipient (e.g.  a plastic tank) by means of two crocodile clips, acting also as probes.  If a deeper sensing level is needed, the clips can be extended by means of two pieces of stiff wire (see pictures). __ Contact: Flavio Dellepiane, fladello @ tin.it

Waterpump Safety Guard for Fish-pond -  The circuit below was developed to guard the fish pond.  In this case to prevent that the pump sucks just air when the water level get below the pump.  When the water filters get saturated and dirty, the water level behind the filter gets to an unacceptable level.  You can see this when the pump also produces air bubbles in the water __ Designed by Tony van Roon  VA3AVR

Wet Bulb Psychrometer -  The LTC2990 is used to monitor system temperatures, voltages and currents. __ Linear Technology/Analog Devices App Note, Oct 26th 2010

Whooper Alarm, #1 -  If you've ever watched any TV at all and seen those old WWII navy movies, you've heard that distinctive "whoop-whoop-whoop" as a destroyer sliced through the waves, guns blazing, and everybody yelling "battle stations!" __ Designed by Tony van Roon  VA3AVR

Whooper Alarm, #2 -  Destroyer Whooper alarm using 5 transistors. __ Designed by Tony van Roon  VA3AVR

Wind Direction & AirFlow Measurement -  The LTC2990 is used to monitor system temperatures, voltages and currents.  Through the I2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC.  The internal 10ppm/°C reference minimizes the number of supporting __ Linear Technology/Analog Devices App Note, Mar 16th 2011

Wire Break Sensor Alarm -  Circuit of a loop sensor based simple security alarm is described here.  The sensor loop is nothing but a short length of thin enamelled copper wire, which bridges two input points of the electronic alarm circuit.  When the loop is opened the alarm circuit fires an active electric/electronic hooter to raise an ear-splitting __ Designed by T.K. Hareendran

Wire Loop Alarm -  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 __ Designed by Aaron Cake

Wire Loop Security Alarm -  A wire is looped through various objects which are to be monitored.  The loop wire is typically an aircraft cable but could also be any insulated stranded wire.  The loop is attached to a table or desk.  Should the loop be cut, the alarm is sounded . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2004

Wire-Break Alarm with Delay -  Here is a simple circuit of wire-break alarm that activates after a delay of 15 to 30 seconds.  When the thin-wire loop running across the entrance door is broken, the alarm __ Electronics Projects for You

Wireless Alarm -  A full featured alarm, nonetheless simble to build.  It features a radio remote control, delayed and immediate wireless sensors, light to show the statusincluding and useful pre-alarm LEDand a relay output to drive a siren.  Inputs for both delayed and immediate "wired" sensors are also provided.  Thanks to the Nutchip, you can customize it to suit your needs, changing the times and the logic. __ Designed by Projects & Ideas from Nutchip.com

Wireless Alarm Transmitter & Receiver -  Here are two circuits that make it possible to add up to eight detectors to an existing alarm system without running a single cable.  Each transmitter has a unique number that is reported to the central unit in the event of an alarm, and the transmitter battery condition is monitored.  must register on this site __ Designed by Published in Elecktor July/Aug, 2010


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


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