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

 

Last Updated: October 24, 2017 02:54 PM

 

Circuits Designed by Dave Johnson, P.E.

Simple Circuit Wire Security Loop Alarm -  A wire loop is used to protect valuable objects in this alarm circuit.  The circuit is powered by a 9v battery.. . . Circuit by David A. Johnson P.E.-December, 2004

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. . . Circuit by Dave Johnson P.E.-October, 2001

Still Another Very Loud piezo Alarm Beeper -  This is yet another beeper circuit that really draws attention.  It sweeps the drive frequency slightly to produce a very annoying sound.  It uses a transformer to increase the drive voltage across the piezo device to more than 200 volts peak to peak . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Touch Alarm for Door Knob -  I designed this hobby circuit many years ago and it seems be a very popular construction project.  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 place . . . Hobby Circuit designed by David A. Johnson P.E.-May, 2000

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

Simple  Smoke Detector -  This simple smoke detector is highly sensitive but inexpensive.  It uses a Darlington-pair amplifier employing two npn transistors and an infrared photo-interrupter module as the sensor.  The circuit gives audio-visual alarm __ Electronics Projects for You

Simple  Suitcase-Lift Alarm -  This suitcase-lift alarm circuit uses vibration sensor HDX-2NC instead of a commercially available sensor.  A home-made mercury switch can also be used instead.  Circuit and working Circuit diagram of the simple suitcase-lift alarm __ Electronics Projects for You

Simple Alert Timer -  This timer is a useful device for people who often forget to turn off devices in time.  Suppose you want to boil water in your electric kettle or cook something on __ Electronics Projects for You

Simple Circuit 6-Input Alarm -  This simple alarm circuit was designed for use in a combined garage and rumpus room.  It can be assembled on Veroboard and uses just one IC plus a handful of cheap components.  The circuit is based on a straightforward 555 timer circuit (IC1).  This is wired as a monostable and sets the siren period which is adjustable up to about three minutes using potentiometer VR1. __ Learning Electronics

Simple Circuit Alarm with telephone dialler interface -  This is the lowest cost dialing alarm on the market and shows what can be done with an 8-pin microcontroller.  The complete circuit is shown below.  You cannot see all the features of this project by looking at the circuitmost of them are contained in the program __ Designed by Colin Mitchell, Talking Electronics

Simple Circuit Alarms -  To use the circuit shown below (left), the diode should be permanently illuminated by a beam of light.  When the light beam is cut, by an intruder, the conductivity of the diode decreases and the alarm sounds.  The alarm will continue to sound, even when the light returns, until the reset switch is pressed.  The value of resistor R is found by experiment but will probably be between 100k and 560k (start with 180k.)  If you want an alarm which sounds when the diode is exposed to light (for example, in order to protect a bag, drawer, suitcase etc) you will need to use the modifications to the circuit shown in the diagram on the right. __ Designed by © David Hoult

Simple Circuit Blown-Fuse Indicator Sounds an Alarm -  10-Jul-08 EDN-Design Ideas A simple blown-fuse-indicator circuit sounds a buzzer and flashes an LED when a fuse blows __ Circuit Design by Vladimir Oleynik, Moscow, Russia

Simple Circuit 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

Simple Circuit Door Alarm -  This is a simple, easy to build, alarm circuit.  For power, I used a small 9-volt battery.  But the circuit itself will work from 5 to 15-volts, just choose a buzzer that's suitable for the voltage

Simple Circuit 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.

Simple Circuit Knock Alarm -  This circuit uses a thin piezoelectric sensor to sense the vibrations generated by knocking on a surface; eg, a door or table.  Basically, it amplifies and processes the signal from the sensor and sounds an alarm for a preset period.  In operation, the piezoelectric sensor converts mechanical vibration into an electrical signal.  This sensor can be attached to a door, a cash box, cupboard, etc using adhesive. __ Raj. K. Gorkhali  c Silicon Chip Electronics

Simple Circuit laser Alarm that gets triggered when beam from a laser pointer is broken -  This circuit is a laser alarm system like the one we see in various movies.  It uses a laser pointer beam to secure your valuables and property.  Essentially, when the beam gets interrupted by a person, animal or object, the resistance of a photodiode will increase and an alarm will be activated.  The laser and the receiver can be fitted in same box, sharing a common power supply. __ Learning Electronics

Simple Circuit Shop-Door Alarm -  Battery-Powered Alarm Circuits:  Attach this circuit to the door of an unattended shop or reception areaand the sound of the buzzer will tell you when you have a customer.  Add a sirenand it becomes a simple intruder alarm.  The Page includes a free SiMetrix circuit simulation. __ Designed by Ron J.

Simple Circuit Touch Alarm -  Touch the sensor of the alarm with your finger and it starts beeping, goes on for some time and then stops.  Touching it again, and it goes again! This little and flexible circuit consists of a touch sensor and a directly coupled transistor amplifier with a small loudspeaker as the output load.  Two sensor strips of metal are __ Designed by T.K. Hareendran

Simple Circuit Transistor Based Motorcycle Alarm -  Motorcycle Alarm Circuits:  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 automaticallyand/or immobilize the machineevery time you turn-off the ignition.  It's easily adapted for a 6-volt systemso it will protect your "Classic Bike". - Now With Free SiMetrix Circuit Simulation. __ Designed by Ron J.

Simple Circuit Wire Security Loop Alarm -  A wire loop is used to protect valuable objects in this alarm circuit.  The circuit is powered by a 9v battery.. . . Circuit by David A. Johnson P.E.-December, 2004

Simple Digital Security SystE - M -  You can use this simple and reliable security system as a watch dog by installing the sensing loops around your building.  You have to stretch the loop wires two feet above __ Electronics Projects for You

Simple, gated, pulsed alarm -  Sometimes the need arises for a simple, gated, pulsed alarm.  The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-done for simplicity.  While it does not offer the most powerful output, it is likely to be adequate for many applications.  A dual CMOS timer IC type 7556 is used for the purpose, __ Learning Electronics

Single Supply Type K Thermocouple Signal Conditioning Amplifier with Cold Junction Compensation -  The LTC2050 is a zero-drift precision chopper stabilized operational amplifier available in the 5- or 6-lead SOT-23 and SO-8 packages.  It minimizes board area while providing uncompromising DC performance, including 3mV (max) DC offset and 30nV/°C (max) DC offset drift.  It operates from a 2.7V supply while still supporting __ Linear Technology/Analog Devices App Note, Apr 9th 2010

Single Zone Alarm -  A single zone alarm circuit with entry and exit delay and other facilities. __ Designed by Andy Collison

Single Zone CMOS Alarm -  This is a single zone alarmwith automatic exit, entry and siren cut-off timers.  It will accommodate all the usual types of normally-closed input devicessuch as magnetic-reed contactsfoil tapePIRs etc. __ Designed by Andy Collison

Single-button lock provides high security -  03/04/99 EDN-Design Ideas (contains several designs, scroll to find this one)   Figure 1 is the block diagram of an easily programmed, single-button combination lock.  You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button.  The circuit uses inexpensive CMOS logic.  The retriggerable timer, T1, locks out entries made after the T1 code-entry window, thereby greatly enhancing security.  The circuit in Figure 2 operates as follows: The Schmitt-trigger quad NAND gate, IC1, debounces the code-entry switch and, with the aid of simple analog circuitry, produces separate outputs for activation times of less than and more than 0.3 sec.  These outputs connect to the select gate, IC5 __ Circuit Design by Maxwell Strange, Fulton,MD

Siren Simulator -  This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail. __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Six-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 __ Designed by Andy Collison

Sleep Switch Cum Wake Up Timer -  Here is a sleep-switch circuit that can be easily converted into a wake-up timer.  A dual-mode time setting makes the system versatile.  The circuit is low-cost and can function as a __ Electronics Projects for You

Small CMOS Alarm Circuits -  Battery-Powered Alarm Circuits:  This is a selection of small self-contained alarm circuits.  They have a very low standby currentand are ideal for battery operation.  Some are triggered by normally-open and normally-closed switches.  And some react to changes in light or temperature.  Included with each is a free SiMetrix circuit simulation. __ Designed by Ron J.

Smart Loop Burglar Alarm -  Simple loop burglar alarms sound whenever the loop breaks.  What if a clever thief comes to know of the working of this alarm? He may simply short the loop by using __ Electronics Projects for You

Smart Smoke Alarm -  At the heart of this ultra simple smoke alarm is H21A1, which is a photo-interrupter module consists of a gallium-arsenide infrared LED coupled to a silicon phototransistor in a plastic housing.  The slot between the infrared sender(LED) and receiver (phototransistor) allows interruption of the signal with smoke, switching the __ Designed by T.K. Hareendran

Smoke Alarm -  The original smoke alarm circuit http://www.  electroschematics.  com/5450/smart-smoke-sensor-alarm/ has some problems and has left some hobbyists and students disappointed.  Rather than to attempt to solve its many problems, I have created an update that uses the venerable LM741 op amp.  It is simpler, more conventional, easier to __ Designed by Jim Keith

Smoke Alarm Battery Life Extender -  While smoke alarms are quite cheap devices, the cost of 9V batteries quickly exceeds their purchase price.  Added to that is the irritation of random beeps from the alarm as the battery reaches the end of its useful life.  This circuit allows typical smoke alarms to be powered from the 12V supply in a burglar alarm while still keeping the standard 9V batteries in place __ Learning Electronics

Smoke Detector -  Smoke Detectors are designed for 3 basic types of system implementations; Standalone, Wireless Connectivity, and Fixed/Wired Connectivity, the first two being battery powered implementations.  Smoke Detectors have 3 main functional blocks; The Sensor and Signal Chain, Processor, and the Communication Interface.  Where the processor and communications interface typically are not needed in your very basic standalone detectors

Smoke Detector -  This home smoke detector circuit warns the user against fire accidents.  It relies on the smoke that is produced in the event of a fire and passes between a bulb and an LDR, the amount of light falling on the LDR decreases.  This type of circuit is called optical smoke detector.  Do not use it as a home smoke detector it’s __ Designed by Popescu Marian

Smoke, Alcohol & LPG-Detection Alarm -  Presented here is a circuit for raising an alarm on detecting smoke or LPG cooking gas leakage, or even alcohol vapours in breath.  This is achieved by using a basic unit __ Electronics Projects for You

Snore Alarm -  The idea behind this snore alarm, is just to rouse the snorer, not the entire household.  To wake the sleeper, vibration is used, not an audible alert.  The vibration is provided by a small motor housed in a small 35mm film case, which can be placed under the sleepers mattress or pillow.  This circuit has a level control and peak display indicator, a variable trigger __ Designed by Andy Collison

Snore Alarm Electronic Device -  Here I describe a little electronic device that detects snoring.  The principle though very simple is efficient and well protected against false triggerings.  Upon detection, it generates a noisy and painfull alarm.  Just what's necessary to wake up everybody except the snorer. __ Designed by chabin laurent

Snow Depth Alarm -  The design of this system alerts a snowplow driver when the snow depth has exceeded four inches.  A visible red LED packaged in a 10mm package is pulsed at a rate of about 50Hz with 10uS pulses.  Twenty four inches away a phototransistor detects the light from the LED.  The LED and the phototransistor are housed in a section of ½ inch PVC pipe, forming a waterproof seal. . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Solar-Powered Intruder Alarm for Sheds & Boats -  Most blokes have got a shedor wish they had! While many people have alarms for their home and cars, a lot of valuable stuff is unprotected in garages and sheds.  It needs protecting and now you can do it with this simple alarm based on a PIR sensor.  It's solar-powered so no mains supply is needed.  And let's not forget boats on mooringsthey need protecting too. __ SiliconChip

Sound operated music bell using 555 timer -  Sometimes ringing the bell manually becomes difficult, especially when you are holding something in your hands. The sound-operated music bell takes care of the problem

Sound Sensor Alarm -  This 6V battery-operated circuit triggers an acoustic piezobuzzer when a sound is detected.  It can also be used as a cheap acoustic-type glass break detector and/or ambient sound level monitor.  The circuit __ Electronics Projects for You

Sound-Operated Intruder Alarm -  When this burglar alarm detects any sound, such as that created by opening of a door or inserting a key into the lock, it starts flashing a light as well as __ Electronics Projects for You

Speed Alarm for Cars; Pt 1 -  Is your license looking a bit a bit dodgey? This compact speed alarm will help you stick to the speed limits. __ SiliconChip

Speed Limit Alarm -  Wireless portable unit; Adaptable with most internal combustion engine vehicles __ Contact: Flavio Dellepiane, fladello @ tin.it

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. . . Circuit by Dave Johnson P.E.-October, 2001

Step Alarm -  This Circuit can monitor the door steps or Staircase.  When a person crosses the steps, the alarm sounds indicating the entry.  The circuit is too sensitive and operates in day light.  The circuit uses an NPN Darlington phototransistor L14F1.  It senses the intensity of light through its exposed base and passes current in the __ Designed by D Mohankumar

Still Another Very Loud piezo Alarm Beeper -  This is yet another beeper circuit that really draws attention.  It sweeps the drive frequency slightly to produce a very annoying sound.  It uses a transformer to increase the drive voltage across the piezo device to more than 200 volts peak to peak . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Sun-Up Alarm -  The SunUp Alarm can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on.  It can also be used to detect a light beam, headlights etc.  The circuit works as follows.  The phototransistor is very sensitive to light.  (Any phototransistor will work fine) __ Designed by Randy Linscott

Sweeping Siren Alarm-3 volts -  A while back I was challenged by a visitor to the website.  He needed a very loud sweeping siren type audio sound generator powered by 3v.  He tried some of the commercial sirens but they were not very loud when powered by 3v.  He also said that those . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2008

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

 


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