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

 

Last Updated: November 30, 2017 07:38 AM

 

Circuits Designed by Dave Johnson, P.E.

Circuit Monitors Power Loss -  For some medical equipment it is important for an operator to know 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 . . . Hobby Circuit designed by David A. Johnson P.E.-March, 1999

Clip-on AC Current Indicator Circuit -  Several times over the last few years I have received calls from people looking for a simple circuit that would tell them when a sump pump or water well pump motor was running.  These people told me that the electrical circuits that turn on and off . . . Hobby Circuit designed by David A. Johnson P.E.-November, 2004

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

Car Alarm Arming Horn Beep Canceller -  It's a great convenience that most modern cars come with a built in alarm, however it is nothing but noise pollution that the horn sounds when the alarm is armed.  Disconnecting the alarm system from the horn relay will eliminate this, but prevent the horn from sounding in the even of an actual alarm.  This circuit serves to silence the arming beep yet maintain the alarm by introducing a small delay into the signal. __ Designed by Aaron Cake

Car Alarm Sound Booster -  For car alarms, emphasis should be put on hearing the audible alert and identifying it as belonging to your ‘wheels’.  Unfortunately, modern car alarm systems seem to have the more or less the same alarm sound — especially if they are from the same brand.  Also.  must register on this site __ Designed by Published in Elecktor July/Aug, 2010

Car anti theft wireless alarm -  This FM radio-controlled antift alarm can be used with any vehicle having 6to 12-volt DC supply system.  The mini VHF, FM transmitter is fitted in  vehicle at night when it is parked in  car porch or car park.  The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in  market at reasonable rate, is kept inside.  Receiver is __ Designed by Radioland.nt.au

Car 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.

Car Anti-Theft Alarm & Immobilizer -  Automobile Alarm Circuits:  This car alarm circuit features Exit and Entry delaysan instant alarm zonean optional intermittent siren outputand an automatic Reset.  By adding external relays you can immobilize the vehicle and flash the lights. __ Designed by Ron J.

Car Anti-Theft Guard -  Here is an easy-to-build car anti-theft guard.  The circuit, shown in Fig.1, is simple and easy to understand.  When key-operated switch S2 of the car is turned on, 12V DC __ Electronics Projects for You

Car Back-up Alarm -  The brake lights of  automobile trigger this circuit on and off.   This save  annoyance of  alarm when it is not needed.   This is an older circuit which was published in Popular Electronics Magazine, but still a good circuit today. __ Designed by Tony van Roon  VA3AVR

Car burglar alarm -  No circuit description, schematic only __ CdS Electronic

Car Porch Guard -  Protect your costly vehicle from theft using this electronic safety system.  The system immediately switches on the porch lamp and sounds a loud alarm as soon as it detects any attempt __ Electronics Projects for You

Carbon Monoxide Alarm -  Carbon monoxide is an insidious poison which canand doeskill.  It's colourless, odourless and sneaks up on you! The first time victims become aware of carbon monoxide poisoning could be too late. __ SiliconChip

Car-Reversing Audio-Visual Alarm -  Here is a simple car-parking alarm circuit based on an AVR microcontroller and an ultrasonic module.  The circuit will alert you while you are reversing your car for parking, if there __ Electronics Projects for You

Car-Reversing Horn with Flasher -  Here is a simple circuit that starts playing the car horn whenever your car is in reverse gear.  The circuit (refer Fig.1) employs dual timer NE556 to generate the sound. __ Electronics Projects for You

Cash Box Guard -  Most thefts happen after midnight when people enter the second phase of sleep called 'paradoxical sleep.' Here is a smart security circuit for your cash box that thwarts the theft attempt __ Electronics Projects for You

Chain Link Fence Alarm -  Long stretches of steel fence can be monitored using the simple circuit below.  An insulated wire is woven through the links in the fence.  Where the fence begins, the circuit is connected to an earth ground and the security wire.  At the end of the fence,. . . Circuit by Dave Johnson P.E.-October, 2005

Cheap Bicycle Alarm -  The author wanted a very cheap and simple alarm for some of his possessions, such as his electrically assisted bicycle.  This alarm is based on a cheap window alarm, which has a time-switch added to it with a 1-minute time-out.  The output pulse of the 555 replaces the reed switch in the window alarm -- must register on this site __ Designed by Published in Elecktor July/Aug, 2010

Cheap 'n' Easy Motorbike Alarm -  It's simple to build, can be fitted to almost any bike and is very easy to operate.  It's armed and disarmed with the ignition key. __ SiliconChip

Circuit forms gamma-photon Detector -  04/24/03  EDN-Design Ideas LED driver delivers constant luminosityThe circuit of Figure 1 includes a PIN photodiode that detects individual photons of gamma radiation.  The reverse bias on the photodiode sometimes creates a depletion region.  When such a ph __ Circuit Design by Bruce Denmark, Maxim Integrated Products, Sunnyvale, CA

Circuit 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

Circuit Monitors Power Loss -  For some medical equipment it is important for an operator to know 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 . . . Hobby Circuit designed by David A. Johnson P.E.-March, 1999

Cistern Overflow Alert SystE - M -  The system presented here will electronically monitor cistern (tank that holds water to flush the toilet) overflows that can otherwise cause seepage in the flats below in a multi-storied building.  In __ Electronics Projects for You

Clear Channel Assessment using TI MSP430 & CC2500 Radio -  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 __ Designed by Texas Instruments App Notes, 31-Jul-07

Clip-on AC Current Indicator Circuit -  Several times over the last few years I have received calls from people looking for a simple circuit that would tell them when a sump pump or water well pump motor was running.  These people told me that the electrical circuits that turn on and off . . . Hobby Circuit designed by David A. Johnson P.E.-November, 2004

Clock/Calendar/Alarm with EEPROM-Based Interpreter & DS Interface -  This is the timekeeping test circuit.  It includes a one-transistor circuit to switch in the 5V power supply when present and drop back to the 3v battery the rest of the time.  That loop of blue wire-wrapping wire is a lariat used to quickly and easily pull the chip out of the socket during development without damage and without having to reach for the removal tool. __ Designed by Dick Cappels

CMOS 4060 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 Ron J.

CMOS 4060 Burglar Alarm -  Single-Zone Burglar Alarm Circuits:  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 contacts, foil tape, PIRs etc.  But it's easy to add a normally-open trigger.  When the alarm is activatedthe siren will sound for a fixed length of time.  Then it will switch offand remain off.  The alarm will not reactivate.  The Circuit Description offers a good introduction to both the CMOS 4060and the SCR. __ Designed by Ron J.

CMOS Based Motorcycle Alarm -  Motorcycle Alarm Circuits:  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.  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.

CMOS Based Single Zone Alarm -  Single-Zone Burglar Alarm Circuits:  This circuit features automatic Exit/Entry delays, timed Bell Cut-off and System Reset.  It has provision for normally-open and normally-closed switches and will accommodate the usual input devices   (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia Sensors). __ Designed by Ron J.

CMOS Based Vehicle Anti-Theft Alarm -  Automobile Alarm Circuits:  This car alarm circuit features Exit and Entry delaysan instant alarm zonean optional intermittent siren outputand an automatic Reset.  By adding external relays you can immobilize the vehicle and flash the lights. __ Designed by Ron J.

CMOS Single Zone 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

CMOS Single Zone Alarm -  Single-Zone Burglar Alarm Circuits:  This circuit features automatic Exit/Entry delays, timed Bell Cut-off and System Reset.  It will accommodate the usual normally-closed input devices   (Magnetic Reed contacts, Micro Switches, Foil Tape and PIRs).  Andwith a simple modificationa normally-open trigger may be added. __ Designed by Ron J.

CMOS single zone intruder alarm -  Alarms and security related electronic circuit diagrams / circuit schematics

Cold Activated Switch -  The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius.  A suitable bead type thermistor is found in the Maplin catalogue.  The 100k pot allows this circuit to trigger over a wide range of temperatures.  A slight amount of hysteresis is provided by inclusion of the 270k resistor.  This prevents relay chatter when temperature is near the switching threshold of this circuit __ Designed by Andy Collison

Combination Digital 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

Combination Lock -  Combination lock are nice to enable alarms, but are useful for controlling a wide range of electric devices.  These software keys can open gates, garages, TV sets, telephones, VCRs, well pumps  In practice this circuit is capable to lock or time all the devices that can be connected to relays. __ Designed by Projects & Ideas from Nutchip.com

Combination Lock -  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

Combination lock -  Operate your gate or something different by this simple electronic combination lock.  The combination can have a chosen length of numbers or alphabets, and can be changed any time.  The LCD display is optional, the circuit works fine without it.  After entering the correct combination, a relay is operated for the predefined time __ Designed by Peter Jakab

Combination Locks -  This circuit uses 4013 D-type bi-stable flip-flops (D stands for data).  Each flip-flop has a data input and a clock input.  The voltage applied to the input is transferred to the Q output at the instant when the clock input goes from 0 to 1.  (We say these flip-flops are "edge-triggered".) Switches 1, 2, 3 and 4 are the switches which form the code and any number of "wrong" switches can be connected, in parallel, at the point shown. __ Designed by © David Hoult

Combination Lock -  a digital lock with keypadenter the correct code to operate a solenoid.  Based around ua3731 __ Contact: P. Townshend EduTek Ltd

Combination Lock2 -  a digital lock with switches.  A nifty circuit i'm chuffed with, based around just 2 logic ics! __ Contact: P. Townshend EduTek Ltd

Complete Type K Thermocouple Measurement System (SPI) with Cold Junction Compensation -  The LTC2484 is ideal for direct digitization of thermocouples and other low voltage output sensors.  The input has a typical offset error of 500nV (2.5μV max) offset drift of 10nV/°C and a noise level of 600nVRMS.  The only signal conditioning is a simple surge protection network.  In any thermocouple meter, the cold junction __ Linear Technology/Analog Devices App Note, Apr 8th 2010

Computer Voltage & Temperature Monitoring -  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

Controller provides multiple alarm-driver formats -  01/15/98 EDN-Design Ideas Using a piezoelectric element for alarm applications offers low cost, low power, and flexibility.  By coupling this element with a 12C508 programmable controller(Microchip Technology, Chandler, AZ], you can implement an eight-pin alarm generator.  This approach provIdeas multiple driver formats with a minimum of additional cost and footprin __ Circuit Design by William Grill, Riverhead Systems, Littleton, CO

Cordless Multidoor Alarm -  Thwart the attempt of burglary by detecting intrusion with this alarm circuit.  Each door is protected by a separate circuit built around an independent 555 timer IC in conjunction with reed __ Electronics Projects for You

Count Down Alarm with 7 LED Segments -  Here I have added two fets for the time-out switch, it is like an electronic relay, just much more reliable it can be used to sound a big horn, or what ever you like. __ Designed by Thomas Scherrer OZ2CPU

Current Limiting Bench Power Supply -  Power Supply Circuits:  This is a 1-amp variable-voltage PSU.  It adjusts from about 3v to 24v: and has the added feature that you can limit the maximum output current.  This is invaluable when   (for example) you power-up a project for the first time or soak-test a piece of equipment. __ Designed by Ron J.

Cut Phone Line Alarm -  Burglars, rapists and other criminals will often cut a phone line before they break into a home.  The cut phone line will prevent many alarm systems from alerting the police.  The battery powered circuit below will sound an alarm when the unit. . . Circuit by David A. Johnson P.E.-October, 2005

Cut Phone Line Detector -  A while ago I got an email asking for the schematic of a circuit to detect cut phone lines.  It didn't take me long to find this circuit in Electronics Now.  When the circuit detects that a phone line has been cut, it activates a MOSFET which can be used to drive a relay, motor, etc.  It can also be connected to a security system __ Designed by Aaron Cake

Cut Phone Line Detector -  This circuit speaks for itself.    When the phone line is okay, Q1 acts as a short with a very high ohms value via R1, R2, and R3 for a total of about 66 MegOhm so very high.  When the phone line is cut (Tony van Roon's open) , it activates the MOSFET (Tony van Roon's Q3) via transistor Q2 to drive the load.    Substitutes are fine, none of the components are critical __ Designed by Tony van Roon  VA3AVR

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


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