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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.

Detect Motion with a Piezo Device   -  Using a piezoelectric device, this circuit will activate a beeper whenever the circuit is moved.    it could be used as an earthquake alarm.   . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Detector for Human Footsteps   -  This circuit uses a surplus geophone to detect human footsteps from 100 feet away.  It was designed for monitoring the Mexico/USA border.  This preamp part of the system draws about 50 micro amps from a 12 volt supply . . . Hobby Circuit designed by Dave Johnson P.E.-July 11, 2006

Detects Low Voltage 120VAC Power Line    -  This hobby circuit will turn on a beeper when the line voltage drops below 100 volt AC . . . Hobby Circuit designed by David A. Johnson P.E.-July 09, 2006

Detects Shadow Activated Motion   -  This circuit can sound an alarm when the shadow of a hand or arm moves over  two small photo diodes . . . Circuit by Dave Johnson P.E.-August 21, 2005

Doggie Water Dispenser Alarm   -  I have two Beagle dogs.  They drink a lot of water; they go through about 3 gallons a week.  They have two water dispensers.  One is on the inside and second unit on the outside of my house.  Often, I forget to fill one of their two jugs and discover them completely empty.  I do worry that my dogs might get dehydrated if I ever forget to fill both of their containers . . . Circuit by David A. Johnson P.E.-June 04, 2012

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 29, 2000

Door Knock Beeper   -  in some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door . . . Circuit by Dave Johnson P.E.-June 14, 2009

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 04, 2000

Earthquake Alarm Circuit   -  Geophones are dandy motion sensors.  They are metal cans containing a powerful magnet, suspended with springs inside a coil of wire.  The magnet functions as a floating mass.  The slightest vertical motion of the device causes the coil to move relative to . . . Hobby Circuit designed by David A. Johnson P.E.-July 08, 2005

Electric Field Disturbance Monitor-Alarm Discriminator + Battery Monitor   -  This schematic is the alarm discriminator plus the battery 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 26, 2002

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.-July 09, 2006

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.-July 09, 2006

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 11, 2006

Freeze Alarm   -  I chose an accurate thermistor from Keystone as the temperature sensor for this circuit.  This device has a very specific resistance at a particular temperature.  According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water.  The thermistor is wired into a simple bridge circuit, which uses 1% resistors.  The bridge is connected to a very low power voltage comparator.  The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value.  At zero degrees C the voltage at the non-inverting input of the comparator exceeds . . . Circuit Solution by Dave Johnson P.E.-May 07, 2006

Freezer Over-Temperature Alarm   -  This circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.   . . . Circuit by Dave Johnson P.E.-July 20, 2006

Freezing Temperature Alarm   -  The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.   . . . Circuit by David Johnson P.E.-November 05, 2014

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 26, 2002

 


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

Darkness Activated Alarm -  Most darkness activated alarms employ opamps and some logic ICs.  Here, a less expensive approach is shown based on the eternal 555, this time in monostable multivibrator mode.  Components R2 and C1 represent a one-second network.  When the LDR (light dependent resistor) is in the dark, its resistance is high, pulling pin 2 of the 555 to ground. __ Learning Electronics

DayLight Alarm -  The circuit presented here wakes you up with a loud alarm at the break of the daylight.  Once again the 555 timer is used here.  It is working as an astable multivibrator at a frequency of about 1kHz. __ Designed by Radioland.nt.au

DC/DC converter operates from phone line -  01/15/98 EDN-Design Ideas DC/DC converters for use inside the telephone handset require operation from the high-source-impedance phone line.  Additionally, the CCITT specifications call for maximum on-hook power consumption of 25 mA. __ Circuit Design by Gary Shockey, Linear Technology Corp, Milpitas, CA

Delayed Audible Alarm -  In this circuit, three multivibrator-type oscillators and a ripple counter are configured to produce an interesting, alarming sound, using two inexpensive integrated circuits plus a few other components. __ Designed by Arthur Harrison

Destroyer Whooper Alarm -  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

Detect Motion with a Piezo Device -  Using a piezoelectric device, this circuit will activate a beeper whenever the circuit is moved.    It could be used as an earthquake alarm. . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Detector for Human Footsteps -  This circuit uses a surplus geophone to detect human footsteps from 100 feet away.  It was designed for monitoring the Mexico/USA border.  This preamp part of the system draws about 50 micro amps from a 12 volt supply . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Detects Low Voltage 120VAC Power Line  -  This hobby circuit will turn on a beeper when the line voltage drops below 100 volt AC . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

Detects Shadow Activated Motion -  This circuit can sound an alarm when the shadow of a hand or arm moves over  two small photo diodes. . . Circuit by Dave Johnson P.E.-August, 2005

Differential Bridge Amplifier -  The LTC2050HV are zero-drift operational amplifi ers available in the 5- or 6-lead SOT-23 and SO-8 packages.  The LTC2050 operates from a single 2.7V to 6V supply.  The LTC2050HV operates on supplies from 2.7V to Ī5.5V.  The current consumption is 800μA and the versions in the 6-lead SOT-23 and SO-8 packages offer power shutdown __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Differential Bridge Amplifier with Gain Programmed through the Serial Interface & Analog to Digital Conversion (Standby Current Less than 100μA) -  The LTC6915 is a precision programmable gain instrumentation amplifier.  The gain can be programmed to 0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, or 4096 through a parallel or serial interface.  The CMRR is typically 125dB with a single 5V supply with any programmed gain.  The offset is below 10μV with a temperature __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Digital Combination Lock -  A multiple input combination loack using CMOS counter IC's.  Flexibility and code change is allowed by changing output connections. __ Designed by Andy Collison

Digital combination lock using paIR of CD4 013 CMOS chips -  The Circuit Board is Designed to accept 2 types of Drive transistors.  I Used a 2N3906 in this schematic, but for Higher Current Drive for a Solenoid, You can use Various T0-220 PNP types of transistors.  USE ONLY ONE OR THE OTHER, NOT BOTH.  In the Picture, I just put a Resistor and LED, where the Solenoid should go. __ Designed by G.L. Chemelec

Digital Electronic Lock -  The digital lock shown below uses 4 common logic ICs to allow controlling a relay by entering a 4 digit number on a keypad.  The first 4 outputs from the CD4017 decade counter (pins 3, 2, 4, 7) are gated __ Designed by Bill Bowden

Digital Keypad Combination Lock -  This simple circuit is the electronic version of the combination lock.  Using the special purpose LS7220 digital lock IC, the circuit allows a 4 digit combination of your choice to activate a relay for a set period of time.  This relay can then be __ Designed by Aaron Cake

Dinner is ready buzzer -  How often on average do you have to call members of your family each day to tell them that dinner is ready, itís time to leave, and the like? The person you want is usually in a different room, such as the hobby room or bedroom.  A powerful buzzer in the room, combined with a pushbutton at the bottom of the stairs or in the kitchen, could be very handy in such situations __ Learning Electronics

Doggie Water Dispenser Alarm -  I have two Beagle dogs.  They drink a lot of water; they go through about 3 gallons a week.  They have two water dispensers.  One is on the inside and second unit on the outside of my house.  Often, I forget to fill one of their two jugs and discover them completely empty.  I do worry that my dogs might get dehydrated if I ever forget to fill both of their containers. . . Circuit by David A. Johnson P.E.-June, 2012

Door Ajar Alarm -  Ever accidentally left your front door ajar and had a pet escape? Here is a smart solution to this problem.  The circuit is fairly simple but a great example of using a tiny circuit to get the job done.  All you need is a CD4011 IC plus a handful of components.  In this door ajar alarm/beeper circuit, a bar magnet-reed switch __ Designed by T.K. Hareendran

Door Ajar Alert -  Have you ever accidentally left your front door ajar and had a pet or your little kid escape? Here is a smart solution to this problem.  This circuit alerts you every __ Electronics Projects for You

Door Alarm -  Hangs up on the door-handle; Beeps when someone touches the door-handle from outside __ Contact: Flavio Dellepiane, fladello @ tin.it

Door Alert -  This circuit can be operated by any kind of switch.  For example, it can be used in a shop to warn that a customer is waiting, with a micro-switch attached to __ Electronics Projects for You

Door chime Privacy Sentry ATtiny12 -  An ATtiny12 controller as a timer and some switching circuitry turns the doorbell off for 10 hours at the same time each day. __ Designed by Dick Cappels

Door Guard -  This door guard uses operational amplifier ĶA741 and a light-dependent resistor (LDR).  Operational amplifier ĶA741 is used as a sensitive voltage comparator.  Preset VR1 provides reference voltage to the non-inverting terminal __ Electronics Projects for You

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

Door knock Alarm with timer -  This low-cost circuit uses the piezoelectric element of a piezobuzzer as the input sensor.  The piezoelectric element plate is fixed at the centre of the door wing by using a cello tape.  Apply a small quantity of adhesive at the edges between the plate and the door.  Extend wires about 1-1.5 metres from the piezoelectric to the circuit. 

Door Knock Beeper -  In some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door. . . Circuit by Dave Johnson P.E.-June, 2009

Door Monitor -  counts the number of times a door is opened.  Counts up to 9 but can be easily expanded __ Contact: P. Townshend EduTek Ltd

Door Sensor -  This compact and affordable door sensor mechanism uses a Hall-effect sensor fixed at the corner of the door frame and a standard bar magnet fixed on the door panel close to the Hall-effect sensor.  When the door is opened, the magnet moves away from the sensor to generate a wake-up signal to the rest of the electronics.  This __ Designed by T.K. Hareendran

Door Timer with Alarm -  We are in a digital era! Now we can add some intelligence to our doors and gates without too much investments.  Just assemble this little door timer circuit built around a few cheap and simple components and link it to any door/gate as per your requirement and taste.  If the door/gate remains in open condition for a prefixed __ Designed by T.K. Hareendran

Door/window sensor resists tampering -  01/21/99 EDN-Design Ideas The simple, inexpensive circuit in Figure 1 detects a failure(or deliberate tampering] on lines connected to normally closed switch sensors.  For example, common door interlocks and door/window sensors consist of normally open or normally closed magnetic reed switches.  Depending Page includes several designs.  Scroll to find this one __ Circuit Design by Paul Nocella, Q Research, Brookline, NH

Doorbell for the Deaf -  This circuit provides a delayed visual indication when a door bell switch is pressed.  In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch.  The lamp can illuminate the words "Please Wait" for anyone with walking difficulties __ Designed by Andy Collison

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

Doorbell with Security Feature -  This doorbell system works such that when someone presses your calling bell switch during the night, not only the bell rings but the bulb connected to it also glows.  In order __ Electronics Projects for You

Doorbell-Controlled Porchlight -  This add-on circuit automatically turns on your porchlight when your doorbell rings, so you can see the person ringing the doorbell at the doorstep.  This also helps to guard against burglars, __ Electronics Projects for You

Doorbell-Controlled Security Switch -  One way to check whether anybody is at home is to ring the doorbell.  Burglars too use this very technique.  The circuit described here comes handy in such a situation.  It __ Electronics Projects for You

Doorbell-Cum-Visitor Indicator -  This doorbell circuit can also give identification of the visitor to your home in your absence.  When youíre home, you can use it simply as a normal doorbell.  The circuit (see Fig. __ Electronics Projects for You

Doorknob touch alarm -  The project was originally intended as a present for my brotherís dorm room, but a bad capacitor and the lack of a proper oscilloscope caused delays.  It has not made it off the breadboard, and it probably will not until his next semester.  The circuit contains a few basic elements, an flip-flop based oscillator, a set of delays, a flip-flop as a sensor, and the audible alarm.   

Door-Knock or Vibration Alarm -  This is a simple circuit that activates an alarm when there is a knock on the door or there are any vibrations due to movement of heavy goods or furniture.  The circuit uses readily available components. __ Electronics Projects for You

Door-Open Alarm -  This door-open alarm uses an input sensor fixed at the corner of the door frame and a magnet fixed on the door panel close to the sensor.  When the door is __ Electronics Projects for You

Door-Opening Alarm -  Children are at a high risk of drowning in a swimming pool.  Majority of accidents occur when children get into a pool unsupervised.  Such situations can be avoided by attaching a __ Electronics Projects for You

Door-Opening Alarm using Hall Sensor -  This simple door-opening alarm uses a hall sensor to produce sound when someone opens the door.  The circuit can be installed at a workshop, office or home for security purposes.  The __ Electronics Projects for You

Drinking Water Alarm -  The State Jal Boards supply water for limited duration in a day.  Time of water supply is decided by the management and the public does not know the same.  In such __ Electronics Projects for You

Driveway Alarm -  You can install this system in the driveway itself to detect intrusion by a vehicle, person or large animal.  It sounds an alarm when any intrusion takes place.As shown in Fig. __ Electronics Projects for You

Dummy Alarm -  This project makes a superbright LED flash briefly once every 5 seconds to imitate the indicator light of a real alarm.  The circuit is designed to use very little current to prolong battery life so that it can be left on permanently.  This is a simple project, ideal for a beginner __ Designed by John Hewes

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

 


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