Alarms of all kinds, electronic circuits, Page 6

Alarm Circuits Page 6
Alarms: #-C D-G H-O P-R S T-U V-Z
Last Updated on: Monday, October 03, 2011 06:08 PM

Circuits Designed by Dave Johnson, P.E.

Unplugged Appliance Alarm
I got a call from an administrator at a large prison. He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens in a commons area. He wanted a battery-powered device, which could be mounted to the outside of the power cord of an appliance. The device would produce a loud alarm whenever the power plug of the appliance was unplugged from a power outlet.......

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

Temperature Alarm Circuit - A simple op-amp circuit that will trigger a relay when a preset temperature is reached. Please note that there is no hysteresis in this circuit, so that if the temperature changes rapidly, then the relay may switch rapidly…. [Circuit design by Andy Collison]

Theft preventer alarm - This circuit utilising a 555 timer IC can be used as an alarm system to prevent the theft of your luggage, burglars breaking into your house etc. The alarms goes ON when a thin wire, usually as thin as a hair is broken. [Radioland.nt.au]

Thermo Alarm - The Th1 thermistor is a regular NTC (Negative Temperature Coeficient) of about 1000 ohms. But other types will work too. Adjust the sensitivity with the 20K trim-pot P1. When the thermistor is at operating temperature, the resistance is high The 330K resistor (R3) is to introduce a little bit hysteresis back on the basis of Q2 to prevent relay chatter.... [Tony van Roon's circuit]

Thief warning device - schematic only, no description included

Three Fake Alarms - Flashing LEDs can be used to create the impression that an alarm has been fitted. Or they can be used in conjunction with a real alarm, to warn-off a potential thief. These three small circuits will flash anything from a single LED, up to 90 LEDs and beyond, with a variety of speeds and patterns.... [Ron J.'s circuit]

Three 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.... [Ron J.'s circuit]

Time to Dust Indicator - I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough. I have not yet built and tested this circuit completely but in concept it should work. The circuit draws very low current from a +3v battery and could be housed in a package similar to a small ashtray. The assembly might be placed in a suitable out of the way area to collect dust. It would alert a maid when it was time to dust the room. The circuit detects dust with an infrared LED that is pulsed so its…. [Designed by David A. Johnson]

Timed Burglar Alarm - This is a simple but effective alarm circuit which can reset its self after a time that you select. it has normally open and normally closed triggers which make this circuit very practical. This alarm has normally open and normally closed triggers. It's on a 555 timer so the alarm will reset it's self after a certain amount of time. The time is adjustable.... (added 10/05)

Tiny 2-zone alarm - Since I travel a lot during summer, I decided to build a really small alarm that could easily fit inside a pocket. However, I also demanded reliable operation, simple construction and very low power consumption. I started with CMOS logic gates, but was soon forced to abandon the concept after a few unsuccessful (and far too complicated) takes.... (Circuit design added 08/08/08)

Tone Control - Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10K and 50Hz. As the controls are passive, the last transistor provides a slight boost. The output…. [Designed by Andy Collison]

Touch Activated Alarm - Not much to tell here as the circuit speaks for itself. The 555 can be almost any type, they are all pin-compatible. Although some CMOS types may not have enough power to drive the transistor, in that case use an ordinary 555. C1's working voltage should be increased to 25V if you decide to go with a 12V power source. Change the value of C1 for the desired output pulse.... [Tony van Roon's circuit]

Touch triggered alarm - No description available.... [Posted by Jospfh]

Transistor Based Motorcycle Alarm - This 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 automatically, and/or immobilize the machine, every time you turn-off the ignition. It's easily adapted for a 6-volt system, so it will protect your "Classic Bike". (Circuit design added 08/08/08)

Travel Touch Alarm - The Travel Touch Alarm can be used to provide a audible alarm when someone touches the door knob or handle of your hotel room. The door knob or handle must be made of metal for the circuit to work. The main chip in the circuit is a 555 timer…. [Circuit design by Randy Linscott]

Two 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]

Two 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 zero - so they won't drain your battery. [Ron J.]

Two-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. [Ron J.'s desoign]

Ultrasonic Remote Control & Alarm - (circuit added 7/02)

Unplugged Appliance Alarm - I got a call from an administrator at a large prison. He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens in a commons area. He wanted a battery-powered device, which could be mounted to the outside of the power cord of an appliance. The device would produce a loud alarm whenever the power plug of the appliance was unplugged from a power outlet....... [Designed by David A. Johnson]

Unplugged Power Cord Alarm - Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries. So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time. The device was designed to snap onto the outside of a power cord, where it senses the AC electric field emitted. No direct connection to the internal wires of the power cord is needed. I also included a low battery voltage monitor.... [Designed by David A. Johnson]

Using the MAXQ3210 in a Light-Beam Alarm System - Maxim App Note 4153 -- 2/26/2008 -- (app note add 5/08)

Alarms: #-C D-G H-O P-R S T-U V-Z