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Alarm Circuits
Alarms:  #'s         A-C         D-F      G-K     
 L -O        P-R        S       
T-U       V-Z

 

Last Updated: April 07, 2016 01:00 PM

 

Circuits Designed by Dave Johnson, P.E.

  • 120 VAC Low Voltage Alarm  -  This circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac. . . . [Circuit by Dave Johnson P.E.,  07/09/06]

  • 3v Sweeping Siren Alarm  -  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 . . . [Circuit by David A. Johnson P.E.,  06/24/08]


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

1 Time Only Alarm -  This alarm is designed to sound its Siren only once. That is - when the alarm is activated - the Siren will sound for a preset length of time. Then it will switch off and remain off. The alarm will not re-activate.The basic circuit has a single zone with independently adjustable Exit and Entry delays… [Circuit designed Ron J.]

 

10 GHz CW Radar based on a X-band Gunnplexer -  This is a modified burglar alarm, based on a X-band Gunnplexer type design. It's interesting, because it has two detector diodes 1/4 wave apart, so you effectively get I/Q demodulation, which allows you to distinguish between approaching and receding doppler. That price was for a pair.… [Jim Lux]

 

12 Volt Alarm Power Supply -  A 12 Volt power suppiled designed for Ron's Modular Burglar Alarm. However, being a popular supply voltage this circuit will have many other uses as well.… [Andy Collison's website]

 

120 VAC Low Voltage Alarm -  This circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac. . . . [Circuit by Dave Johnson P.E.,  07/09/06]

 

1-IC Design Monitors Ajar Doors -  11/05/12  EDN Design Idea   This design senses an ajar door and, if the situation isn’t corrected within 20 sec, sounds a beeping alarm.… [by Fred Hicks, General Electric Co, Louisville, KY ]

 

1-Time-Only Burglar Alarm -  When this alarm is activated its Siren will sound once, for up to 20-minutes. Then it will switch off and remain off. The basic circuit has a single zone with independently adjustable Exit and Entry delays.This will be adequate in many situations. However,… [Ron J.'s circuit]

 

2 CMOS Based Vehicle Anti-Hijack Alarms -  The first circuit is designed for the situation where a hijacker forces the driver from the vehicle. If a door is opened while the ignition is switched on - the circuit will trip. After a few minutes delay - when the thief is at a safe distance - the alarm will sound and the engine will fail. The second circuit is a modification of the first - offering enhanced protection in many more situations.… [Ron J.'s circuit]

 

2 Simple Relay Based Motorcycle Alarms -  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 zeroso they won't drain your battery.… [Ron J.'s circuit]

 

2 Zone Intruder Alarm -  This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devicessuch as magnetic reed contacts - foil tape - PIRs etc. I've used a 12-volt supply in the diagram - but the circuit will work at anything from 9 to 15-volts. All you need do is select a siren, buzzer and relay to suit the voltage you want to use… [Circuit designed by Ron J.]

 

2-input alarm -  This article describes a 2-Input alarm developed on the PIC LICK-1 Module using a Microchip PIC16F628-04.  The program uses the internal 4MHz oscillator and if any other frequency is used, the timer values will need to be changed … [email Colin Mitchell: talking AT tpg.com.au]

 

2-Zone Burglar Alarm -  This two-zone alarm has automatic exit, entry and siren cut-off timers. It was developed for the Beginner's Guide To Cmos Timers. So it has a particularly detailed circuit description. There's an optional One-Time-Only module. It will force the siren to switch off after the first ten minutes - and prevent the alarm from activating a second time. … [Electronic design by Ron J.]

 

3 Flashing LED Doorbells -  These circuits combine a buzzer with one or more LED displays. When the push switch is operated - the buzzer will sound and the LEDs will flash. When the switch is released - the buzzer will stop - but the LEDs will go on flashing for another 30 seconds or so.… [Electronic design by Ron J.]

 

3 Zone Duress Alarm -  This is a 3 zone alarm for use in high risk areas or possible duress situations. Typical examples being banking or betting booths. The alarm consists of 3 normally open push button switches which can be hidden or in plain view. Once pressed the alarm will latch and a LED will light showing which zone has pressed the alarm… [Circuit by Andy Collison]

 

3v Sweeping Siren Alarm -  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 . . . [Circuit by David A. Johnson P.E.,  06/24/08]

 

4 Digit Keypad -  This is an enhanced 4 digit keypad which may be used with the Modular Alarm System… [Circuit design by Ron J.]

 

4 in 1 Burglar Alarm -  In this circuit, the alarm will be switched on under the following four different conditions: 1. When light falls on LDR1 (at the entry to the premises). 2. When light falling on LDR2 is obstructed. 3. When door switches are opened or a wire is broken. 4. When a handle is touched. The light dependent resistor LDR1 should be placed in darkness near the door lock or handle etc. If an intruder flashes his torch… [Radioland.nt.au]

 

4-Digit Alarm Control Keypad -  This Keypad is suitable for the Modular Burglar Alarm. However, it has other applications. Pressing a single key will energize the relay. Entering the Four-Digit code of your choice will de-energize it.  … [Ron J.'s circuit]

 

4-Digit Keypad Controlled Switch -  This is a Universal version of the Four-Digit Alarm Control Keypad. I have modified the design to free up the relay contacts.This allows the circuit to operate as a general-purpose switch. I've used a SPCO/SPDT relay, but you can use a multi-pole relay if you wish… [Electronic design by Ron J.]

 

5 Digit Alarm Keypad -  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… [Andy Collison's website]

 

5 Zone Alarm Circuit -  This is a complete alarm system with 5 independent zones suitable for a small office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a "system armed" indicator.… Andy Collinson

 

5 Zone Alarm System -  Alarms and security related electronic circuit diagrams / circuit schematics… [designed by Andy Collison]

 

555 Door Ajar Flasher -  A magnet is placed on the door and a magnetic reed switch on the door casing so when the door is closed the circuit is disabled. When the door is open, the LED flashes VERY BRIGHTLY—when closed, the circuit is disabled in such a way that it draws virtually no current for maximum battery life. Door Ajar LED Light Schematic Bill… [Circuit posted by Jim Keith]

 

555-Timer Based Motorcycle Alarm -  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. Now With Free SIMetrix Circuit Simulation.… [Ron J.'s circuit]

 

5-Digit Alarm Control Keypad -  This Keypad is suitable for the Modular Burglar Alarm. However, it has other applications. Entering the First Four Digits of your chosen Five-Digit code, will energize the relay. Entering the Full Five-Digit code, will de-energize it.  … [Ron J.'s circuit]

 

6 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… [Andy Collison, designer]

 

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Alarms:  #'s          A-C         D-F        G-K      L -O       P-R         S        T-U       V-Z


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