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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.

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

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

 

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

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, 2002

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

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, 2005

Earthquake Detector -  Here is an ultra sensitive earthquake detector circuit that can sense seismic vibrations.  It can be used to detect vibrations in the Earth.  So it is an ideal device to monitor entry passages.  The circuit exploits the direct piezo electric property of the piezo element used in buzzers.  The Lead Zirconate crystals present in the __ Designed by D Mohankumar

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

Electrolytic capacitor-based data backup power solution for a 12V system with 5V to 36V input -  EDN-Design Ideas 11/30/2016    This module provIdeas hold-up power in e.   g., embedded systems, and can also be combined with a buck-boost module for a robust power system suitable __ Circuit Design by LTC Design Note

Electronic Buzzer -  This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC.  The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on.  The frequency can be changed by varying the 10K resistor. 

Electronic buzzer -  This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC.  The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on.  The frequency can be changed by varying the 10K resistor __ Designed by Radioland.nt.au

Electronic Canary Doorbell -  This circuit is a modified "Hartley Oscillator" with a couple extra parts.    T1, the LT700 (Tony van Roon's or equivalent, is a small center tapped (Tony van Roon's ct) audio transformer with an impedance of 1000 ohms at 1000 hertz.    The secondary of this transformer has an impedance of 8 ohms.    Usually noted as 1K:8 ct.    I tried a couple other models like the red and green types (Tony van Roon's taken out of a $5 made-in-china am pocket radio) and they both work good.    You may have to adjust the caps to get the sound __ Designed by Tony van Roon  VA3AVR

Electronic Chime -  Scroll Down to find this circuit.  This circuit simulates a chime similar to the sound many cars make when the keys are left in the ignition.  The bottom two gates form a squarewave audio oscillator that drives the base of the 2N4401, turning it on and off at an audio rate.  The top two gates produce a short low-going pulse about once per second that discharges the 10 uF capacitor through the diode.  The voltage then jumps up and slowly decays __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Electronic Combination Lock -  This 7-digit combination lock can be easily hard-wired for any combination that you choose.  The circuit uses a 4-bit, divide-by-8 Johnson counter (IC1), ten pushbutton switches and npn transistor T1.  At power-‘on,’ __ Electronics Projects for You

Electronic combination lock based on PIC -  This is my electronic combination lock to use with an outdoor gate.  The functionality is implemented in software.  It turns on a relay (usually to open a door) for a few seconds.  Uses a PIC16F84A. __ Designed by Peter Jakab

Electronic Combination Lock with AVR -  CodeLock AVR electronic combination lock is realised with Atmel AVR microcontroller AT89C2051 or AT90S2313 or ATtiny2313 or ATtiny45.  Program in hex code is 2 kB long.  One user code (Ver.1) is consisted of 1 to 8 digits.  One user code (Ver.2.1, 2.2, 2.3) is consisted of 1 to 4 digits.  If you buy the chip (Ver.2.1, 2.2, 2.3) than you can enter 1 or 8 user codes that are consisted of 1 to 9 digits. 

Electronic door codelock PIC16F84 -  This is my electronic combination lock to use with an outdoor gate.  The functionality is implemented in software.  It turns on a relay (usually to open a door) for a few seconds if someone enters the valid code.  Alternatively, it works as an ON/OFF switch, which toggles the relay each time the code is entered __ Designed by Peter Jakab

Electronic Door Release -  Keypad-Operated Door-Lock Release:  This circuit is designed to operate an electrical door-release mechanismbut it will have other applications.  When you enter the four-digit code of your choicethe relay will energize for a preset time period.  Use the relay contacts to power the release mechanism.  The standby current is virtually zeroso battery power is a realistic option. __ Designed by Ron J.

Electronic Gate Keeper -  This circuit can do the job of a Gatekeeper and alerts you if someone passes through the gate.  The alarm can be an AC bell or a Lamp.  The alarm turns on for 1 minute and stops if the light barrier is restored again.  Infrared rays are used as the light barrier to activate the

Electronic KeypA - D -  The IC is a quad 2 input "AND" gate, a CMOS 4081.  These gates only produce a HIGH output, when BOTH the inputs are HIGH.  When the key wired to 'E' is pressed, current through R1 and D1 switchs Q5 on.  The relay energises; and Q5 is 'latched on' by R8.  Thus, the Alarm is set by pressing a single key, say one of the two non-numeric symbols __ Designed by Ron J.

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

Electronic Locker Guard -  Protect your Locker or Briefcase from theft using this pocket sized gadget.  It gives a loud police siren to catch attention.  The circuit uses a single IC and a few discrete components.  It works on the principle of light detection by LDR.  When the unit is in dark, LDR cease to conduct and the alarm generator does not get power __ Designed by D Mohankumar

Electronic Reminder -  This easy-to-build electronic alarm will remind you of an impotant task after a preset time.  It is particularly useful for housewives and busy professionals.  All you have to do is set __ Electronics Projects for You

Electronic Water Alarm -  Aburst water-supply hose of the washing machine, a bathroom tap that you forgot to close, or a broken aquarium wall may turn your house into a pond.  You can avoid this __ Electronics Projects for You

Electronics Card-Lock SystE - M -  The circuit presented here can be used as a lock for important electronic/electrical appliances.  When card is inserted inside its mechanism, depending upon the position of punched hole on the card, a __ Electronics Projects for You

Emergency Light & Alarm -  Powered by two AA NI-CD batteries; Four switchable options __ Contact: Flavio Dellepiane, fladello @ tin.it

Emergency 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.

Enhanced 4 Digit Alarm KeypA - D -  This is an enhanced 4 digit keypad which may be used with the Modular Alarm System __ Designed by Ron J.

Enhanced 5 Digit Alarm KeypA - D -  This is an enhanced 5 digit keypad which may be used with the Modular Alarm System.  This switch will suit the Modular Burglar Alarm circuit.  However, it also has other applications.  The Keypad must be the kind with a common terminal and a separate connection for each key.  On a 12-key pad, look for 13 terminals.  The matrix type with 7 terminals will NOT do.  Choose the five keys __ Designed by Andy Collison

Enhanced Shed / Garage Alarm -  Battery-Powered Alarm Circuits:  This is an enhanced version of the simple Garage/Shed Alarm.  The Entry and Exit delays have been increased to about 30-secondsand I've added a timed Siren cut-off and automatic Reset.  I've also replaced the LED with an entry Buzzer.  These enhancements mean that the new version will have a much wider application. __ Designed by Ron J.

Entry Alarm This is an Infrared based Broken beam alarm to protect doors and entry passages.  It gives a loud alarm when somebody crosses the Invisible Infrared barrier.  It can protect the doors both day and night and is free from false triggering.  The circuit is too simple and can be a good evening project for the hobbyists.  The circuit __ Designed by D Mohankumar

Estimating available applicaiton power for Power-over-Ethernet applications -  Many existing Ethernet devices are being converted from wall-adapter power sources to utilize the newly released IEEE 802.3af Power-over-Ethernet (PoE) standard.  Powersystem efficiency formerly was not much of an issue with a wall adapter—but PoE changes that. __ Designed by Texas Instruments App Notes, SLYT085

Ethernet based Security SystE - M -  The need for Security systems have rapidly grown from being specialized for high-risk areas (like banks, companies , governmental institutions), to be available and demanded rapidly by the average public.  In the last ten years, small businesses have rapidly grown and expanded and the need of reliable, cheap and effective security system is becoming a must ,not only for the business owners ,but also at homes __ Contact: IQ Technologies

Everything-that-moves alarm -  A crucial failing of proximity detectors is their unreliable and tricky nature.  This is where they are used to detect humans, not to speak of smaller living beings.  One common approach is to detect __ Designed by © Rev. Thomas Scarborough

Expandable Multi-Zone Modular Burglar Alarm -  Multi-Zone Burglar Alarm Circuits:  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.  By using the Expansion Modules, you can add as many zones as you require; some or all of which may be the inertia   (shock) sensor type. __ Designed by Ron J.

Expandable SCR Based Burglar Alarm -  Multi-Zone Burglar Alarm Circuits:  This is a simple SCR based burglar alarm circuit.  Its features include automatic Exit and Entry delaystogether with a timed Bell Cut-off and Reset.  The basic alarm has a single zone.  This will be adequate in many situations.  Howeverthe modular design means that you can add as many zones as you like to the system.  Details of a Four-Zone expansion module are provided. __ Designed by Ron J.

Expandable Transistor Based Burglar Alarm -  Multi-Zone Burglar Alarm Circuits:  This transistor based alarm features automatic Exit and Entry delaystogether with a timed Bell Cut-off and system Reset.  Along with the Exit/Entry zonethe basic alarm board has one Instant Zone.  This will be adequate in many situations.  Howeverthe modular design means that it's easy to add as many zones as you like to the system.  Details of a Four-Zone expansion module are provided. __ Designed by Ron J.

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

 


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