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

 

Last Updated: October 18, 2017 05:04 AM

 

Circuits Designed by Dave Johnson, P.E.

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 . . . Circuit by Dave Johnson P.E.-June 04, 2000

Monitors Pump Motor   -  This circuit solves this problem in a novel way.  It clips on the outside of the pump motor’s power cable and provides a transistor switch closure whenever the circuit detects current flowing to the motor.  The circuit draws so little current that a small lithium cell will power the circuit for years . . . Circuit Solution by David A. Johnson P.E.-November 18, 2004

Motion Alarm using piezo Device   -  An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm . . . Circuit by David Johnson P.E.-July 09, 2006

Next-Generation Star-Trek Doorbell   -  in the Star Trek “Next Generation” TV series, the doorbell outside the private quarters of a crew member makes a particular “beep-boop” sound.  The 3v battery powered circuit below tries to simulate this sound.  The circuit uses one 74HCT74 dual D flip/flop . . . Hobby Circuit designed by Dave Johnson P.E.-October 12, 2001

Over-Temperature Micro-Power 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 . . . Hobby Circuit designed by David Johnson P.E.-June 04, 2000

Piezoelectric Device used for Motion Alarm   -  An inexpensive piezo wafer is used to detect vibration and when the vibration is sufficient a switch is activated . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

Power Line Alarm   -  This circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac.   . . . Circuit by David Johnson P.E.-July 09, 2006

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 . . . Circuit by David Johnson P.E.-March 26, 1999

Pump Motor Monitor   -  This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on.  It is designed to detect the motor current using a small inductor placed on the outside of the motor’s power cable.  No direct wire contact is needed . . . Circuit by David Johnson P.E.-November 18, 2004


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

Mains Box Heat Monitor -  This simple circuit monitors the mains distribution box constantly and sounds an alarm when it senses a high temperature due to overheating, helping to prevent disasters caused by any sparking in the mains box due to short circuits.  It also automatically switches on a bright white LED when the power fails.  The LED gives ample light to check the mains box wiring or fuses in darkness.  The circuit beeps once when power fails and again when power resumes. __ Designed by D. Mohan Kumar

Mains Failure/Resumption Alarm -  This mains indicator sounds an alarm whenever AC mains fails or resumes.  It is very useful in industrial installations, cinema halls, hospitals, etc. __ Designed by V. David

Mains Remote-Alert -  Remotely-operates a Beeper and/or a LED via mains supply line __ Contact: IQ Technologies

Mains Supply Failure Alarm -  When ever AC mains supply fails, this circuit alerts you by sounding an alarm.  It also provides a backup light to help you find your way to the torch or the __ Electronics Projects for You

Mains Supply Failure Alarm -  Whenever AC mains supply fails, this circuit alerts you by sounding an alarm.  It also provides a backup light to help you find your way to the torch or the generator key in the dark.  The circuit is powered directly by a 9V PP3/6F22 compact battery.  Pressing of switch S1 provides the 9V power supply to the circuit.  A red LED (LED2), in conjunction with zener diode ZD1 (6V), is used to indicate the battery power level. __ Learning Electronics

Make a Fire-alarm System for Your House! -  Many buildings and homes need smoke detectors to alarm at the initial stage of a developing fire accident.  To prevent damage, smoke detectors perform… __ Designed by Upasana Dewan

Mat Switch -  This Simple Circuit Produces A Warning Beep When Somebody Crosses A Protected Area In Your Home Or Office.  The Switch, Hidden Below The Floor Mat, Triggers The Alarm When The Person __ Electronics Projects for You

May Save Property & Life -  05/13/10 EDN-Design Ideas The circuit in Figure 1 sounds an alarm whenever the perimeter- protection line—a thin copper wire of appropriate length—breaks.  You can get the thin wire from a used relay coil.  Place the wire around a tent, a camping area, or a __ Circuit Design by Vladimir Oleynik, Moscow, Russia

Medical timer warns when pills are due -  05/10/01 EDN-Design Ideas Some people need to take medication at precise, regular intervals.  When you're in a hospital, a medical staff is present to ensure that you take your medication on time.  But when you're taking medication at home, you must frequently look at the clock-a clear annoyance.  When my wife was pregnant, she needed to take medication every two hours from 8 am to 10 pm.  To help her time the two-hour intervals, I built the battery-powered circuit in Figure 1.  The circuit derives its power from a 9V PP3 battery.  All the ICs are CMOS -based; the low power consumption of the circuit allows one-week autonomy.  When you press the start button, BP1, a two-hour delay commences. __ Circuit Design by J Terrade

Melody generator for greeting cards -  his tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell. 
There is not much to the circuit.  The UM66 is connected to its suppl. __ Designed by Radioland.nt.au

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

Micropower Thermocouple Signal Conditioner with Cold Junction Compensation -  A thermistor, shown as R3, is used to monitor the cold junction temperature.  Its resistance becomes smaller as the cold junction temperature increases.  An increase in cold junction temperature will reduce the output voltage of the Type J thermocouple by 52uV/C.  The voltage reference and scaling of resistor values creates an __ Linear Technology/Analog Devices App Note, Jun 21st 2011

Microwave Motion Detector -  Schematic only __ Designed by va3iul

Midnight Security Light -  Most thefts happen after midnight hours when people enter the second phase of sleep called ‘paradoxical’ sleep.  Here is an energy-saving circuit that causes the thieves to abort the theft attempt by lighting up the possible sites of intrusion (such as kitchen or backyard of your house) at around 1:00 am.  It automatically resets in the morning.  The circuit is fully automatic and uses a CMOS IC CD 4060 to get the desired time delay.  Light-dependent resistor LDR1 controls reset pin 12 of IC1 for its automatic action. __ Electronics Projects for You

Mini Alarms -  This is a selection of small self-contained alarm circuits.  They have a very low standby current; and are suitable for battery operation. __ Designed by Ron J

Mini Alarm-Suitable for doors & windows, Portable anti-bag-snatching unit -  This circuit, enclosed in a small plastic box, can be placed into a bag or handbag.  A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord.  If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts oscillating and the loudspeaker emits a loud alarm sound.  A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a small loudspeaker.  Low part-count and 3V battery supply allow a very compact construction. __ Learning Electronics

Miniature Loop Alarm -  A few months ago, I decided to build a compact, yet effective alarm.  My demands were:- simple construction, reliable operation, very small power consumption, and, most of all, small size.  I started with CMOS logic gates, but was soon forced to abandon the concept after a few unsuccessful (and far too complicated) attempts.  Then I suddenly realized that a simple transistor switch might do the job and I was right.

Mock Alarm with Call Bell -  Here is a fully automatic mock alarm to ward off any intruder to your house.  The alarm becomes active at sunset and remains ‘on’ till morning.  The flashing light-emitting diodes (LEDs) __ Electronics Projects for You

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.  It is connected permanently to the 12-volt supply and its operation is "enabled" by opening SW1l __ Designed by Ron J

Monitor Alarm & Indicator Display Multiple Deviation Boundaries -  22-April-10 EDN-Design Ideas Use a microcontroller and its ADCs to indicate process errors. __ Circuit Design by William Grill, Riverhead Systems, Lenexa, KS

Monitors Pump Motor -  This circuit solves this problem in a novel way.  It clips on the outside of the pump motor’s power cable and provides a transistor switch closure whenever the circuit detects current flowing to the motor.  The circuit draws so little current that a small lithium cell will power the circuit for yearsCircuit Solution by David A. Johnson P.E.-November, 2004

Motion Activated Switch for Alarm, Light or Water Sprinkler -  The motion sensor switch circuit can automatically turn on a water sprinkler but you can easily use it as a motion sensor light switch or motion activated alarm too.  Before beginning the construction contact your nearest electronics component vendor and procure a readymade box-type Passive Infrared (PIR) Motion Sensor unit. __  Designed by T.K. Hareendran

Motion Alarm using piezo Device -  An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm. . . Circuit by David Johnson P.E.-July, 2006

Motion Detector Alarm -  This motion detector alarm circuit can detect a moving person from a distance of 1 meter.  It uses a Dual IR Transmitter-Receiver module HOA1405.  When the sensor detects the reflected IR rays, Alarm will sound for 2 minutes.  The circuit can be modified for various applications including AC operated alarm systems.  Motion __ Designed by D Mohankumar

Motor Protection/Regulation -  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. __ Linear Technology/Analog Devices App Note, Oct 26th 2010

Motor Protection/Regulation-LTC2991 -  The LTC2991 is used to monitor system temperatures, voltages and currents.  Through the I2C serial interface, the eight monitors can individually measure supply voltages and can be paired for differential measurements of current sense resistors or temperature sensing transistors.  Additional measurements include internal temperature __ Linear Technology/Analog Devices App Note, Sep 7th 2011

Motorbike Alarm -  This simple-to-build alarm can be fitted in bikes to protect them from being stolen.  The tiny circuit can be hidden anywhere, without any complicated wiring.  Virtually, it suits all bikes as __ Electronics Projects for You

Motorcycle Alarm -  Any number of normally open switches may be used.  Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand.  Use micro-switches to protect removable panels and the lids of panniers etc.  While at least one switch remains closed, the siren will sound.  About two minutes after the switches have been opened again, the alarm will reset. __ Designed by Ron J

Motorcycle Alarm #3 -  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. __ Designed by Andy Collison

Motorcycle Alarm #4 -  This is a simple easy to build transistor based motorcycle alarm.  It's designed to work at 12-volts.  But if you change the relay for one with a 6-volt coil it'll protect your "Classic Bike".  The standby current is virtually zero so it won't drain your battery. __ Designed by Andy Collison

Motorcycle Alarm #7 -  Motorcycle Alarm Circuits:  This is a simple transistor alarmwith a siren cut-off timer.  While the thief continues to move the bikeand the normally-open trigger switch continues to open and closethe siren will continue to sound.  Shortly after the bike stops movingthe siren switches offand the alarm resets. __ Designed by Ron J.

Motorcycle Alarm #8 -  Motorcycle Alarm Circuits:  This transistor alarm has a siren cut-off timerand an LED activation indicator.  Shortly after the thief abandons the bikethe siren will switch off and the alarm will reset.  If the LED is lighting when you returnyou'll know there's been an activation while you were away. __ Designed by Ron J.

Motorcycle Alarms #5 & #6 -  These are two easy to build relay-based alarms.  You can use them to protect your motorcycle but they have many more applications.  If you use relays with 6-volt coils they'll protect your "Classic Bike".  Both alarms are very small.  The completed boards occupy about half a cubic-inch 8 cc.  The standby current is zero so they won't drain your battery.  Circuit designed by Ron J. __ Designed by Andy Collison

Motorcyle Alarm #2 -  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.  Ron has used my Asymmetric Timer as the basis for his design __ Designed by Ron J.

Multidoor Opening Alarm with Indicator -  This door-opening alarm alerts you of intruders.  You can use it for up to three doors.  You simply need to fit a small unit including reed switch on each doorframe and fix __ Electronics Projects for You

Multi-Tone Configurable Alarm -  Presented here is a multi-tone configurable alarm that can be activated by temperature and other physical parameters.  Its output tone can be selected through different switch combinations.  Such an alarm is __ Electronics Projects for You

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

 


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