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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.

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:

Telephone Dialler for Burglar Alarms -  Esy-to-build circuit dials a pre-programmed number via a modem and sends a warning tone if your alarm is triggered __ SiliconChip

Temperature Monitor using 741 opamp -  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. __ Designed by Andy Collison

Temperature Monitor with Alarm -  This temperature monitor alarm circuit continuosly monitors the room temperature and beeps when the temperature drops below 20 degrees centigrade.  This capability to constantly monitor the room temperature can help lower your air-conditioning costs by reminding you to turn off your airconditioner.  An optical display like a __ Designed by Popescu Marian

Temperature Monitoring with an NTC Thermistor While Measuring Load Current & LTC4151 Supply Current -  The LTC4151 is a high side power monitor that operates over a wide voltage range of 7V to 80V.  In default operation mode, the onboard 12-bit ADC continuously measures high side current, input voltage and an external voltage.  Data is reported through the I2C interface when polled by a host.  The LTC4151 can also perform on-demand __ Linear Technology/Analog Devices App Note, Apr 26th 2010

Temperature Sensor Control -  A basic circuit using Diodes to detect temperature differences __ Designed by G.L. Chemelec

Temperature to Frequency Converter -  3% Linearity from –20°C (Fout = 20kHz) to 75°C (Fout = 25kHz) The LTC6990 is a precision silicon oscillator with a programmable frequency range of 488Hz to 2MHz.  It can be used as a fixed-frequency or voltage-controlled oscillator (VCO).  The LTC6990 is part of the TimerBlox family of versatile silicon timing devices. __ Linear Technology/Analog Devices App Note, Jun 16th 2010

Temperature-to-Frequency Converter -  Precision oscillator structure uses SCR effect to discharge integration capacitor.  A temperature dependent device (LM134) effects the integrator trip point to form a variable interval.  An output transistor detects the reset action and forms a logic pulse. __ Linear Technology/Analog Devices App Note, Jun 21, 2011

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. __ Designed by Radioland.nt.au

Thermal Proximity Detector using a RPW100 -  Schematic only __ Designed by va3iul

Thermally Controlled NiCad Charger -  A voltage controlled current (maximum of 1A) is used to charge a NiCd battery.  The control voltage is derived from the temperature difference between the battery and the ambient air.  The charge current is reduced as the battery heats up. __ Linear Technology/Analog Devices App Note, Jun 21, 2011

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 __ Designed by Tony van Roon  VA3AVR

Thermocouple Thermometer with Cold Junction Compensation -  The LTC2997 is a high-accuracy analog output temperature sensor. __ Linear Technology/Analog Devices App Note, Jul 7th 2011

Thermostat Control for Electric Heaters -  One Advantage of these two units is the Sensor can be placed Away from the heater, therefore sensing the Actual Room temperature, not the direct heat from the heater.  These can also be used in a confined space with a Heat Lamp, to create a Drying Oven __ Designed by G.L. Chemelec

Thief warning Device -  schematic only, no description included

Three Flashing LED Doorbells -  Battery Powered LED Circuits:  These circuits combine a buzzer with one or more LED displays.  When the push switch is operatedthe buzzer will sound and the LEDs will flash.  When the switch is releasedthe buzzer will stopbut the LEDs will go on flashing for another 30 seconds or so. __ Designed by Ron J.

Tilt Sensor Alarm -  Ultra simple circuit of the tilt sensor alarm presented here can be fabricated using readily available inexpensive components.  The circuit is a true transistor based design.  Home made Tilt sensor for this circuit is an ordinary little glass/plastic bottle with two metal needles inserted through its cap, and a small quantity of __ Designed by T.K. Hareendran

Time to Dust -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Hobby Circuit designed by David A. Johnson P.E.-May, 2006

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 

Timer for Geyser -  This timer circuit for geyser sounds an alarm after the set timing of 22 minutes when the water is heated up.  The circuit comprises a timer IC 555 wired as an astable __ Electronics Projects for You

Timer warns when pills are due -  05/10/01 EDN-Design Ideas Some people need to take medication at precise, regular intervals.  When you're in a hospital, a medical staff is present to ensure that you take your medication on time.  But when you're taking medication at home, you must frequently look at the clock-a clear annoyance.  When my wife was pregnant, she needed to take medication every two hours from 8 am to 10 pm.  To help her time the two-hour intervals, I built the battery-powered circuit in Figure 1.  The circuit derives its power from a 9V PP3 battery.  All the ICs are CMOS -based; the low power consumption of the circuit allows one-week autonomy.  When you press the start button, BP1, a two-hour delay commences. __ Circuit Design by J Terrade

Timer with Alarm -  This simple alarm timer circuit is made with 4060 which has an integrated oscillator with a good stability with a relatively wide frequency range.  In the circuit diagram the oscillator frequency is set by the RC network that is connected at pins 9, 10 and 11.  When the timer with alarm circuit is connected with S1, the pulse __ Designed by Popescu Marian

Timer with Musical Alarm -  This low-cost timer can be used for introducing a delay of one minute to two hours.  After the timing period is over, a musical song is heard.  The circuit is built around __ Electronics Projects for You

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 __ copy of geocities.com/tomzi.geo page

Tiny Door Guard with Alarm -  This simple Door Chime protects the door and gives a loud Alarm tone when there is an attempt of theft.  The circuit is too simple and battery operated.  A Normally Closed (NC) reed switch and magnet is used to trigger the circuit.  Alarm generator is the popular ROM IC UM 3561.  This 8 pin IC has an inbuilt oscillator to generate __ Designed by D Mohankumar

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 __ Designed by Tony van Roon  VA3AVR

Touch Alarm -  This is a new type of touch alarm that uses an RF oscillator at its input.  One special feature of this touch alarm is that it can use a big-size touch __ Electronics Projects for You

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

Touch triggered alarm -  No description available __ Designed by Jospfh

Transistor Based Motorcycle Alarm -  Motorcycle Alarm Circuits:  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 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.

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.

Transistor based Security Siren -  This circuit was requested by several correspondents.  Its purpose was to obtain more power than the siren circuit already available on this website (One-IC two-tones Siren) and to avoid the use of ICs.  A complementary transistor pair (Q2 & Q3) is wired as a high efficiency oscillator, directly driving the loudspeaker.  Q1 ensures a full charge of C2 when power is applied to the circuit __ Learning Electronics

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

Transistor based single zone intruder alarm -  This circuit features automatic Exit and Entry delays – timed bell cut-off – and system reset.  It has provision for normally-open and normally-closed switches – and will suit all of the usual input devices (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia Sensors). 

Transistor Delays to Detect if a door is open for a long period -  You're charging the capacitor directly from the battery.  So the charging time is related to the product RC, where R is just the internal resistance of the battery.

Two CMOS Based 24-Hour Timers -  Timer Circuits:  A pair of multi-range timers offering periods of up to 24 hours and beyond.  Both are essentially the same.  The main difference is, that when the time runs out, Version 1 energizes the relay and Version 2 de-energizes it.  The first uses less power while the timer is running; and the second uses less power after the timer stops.  Pick the one that best suits your application. __ Designed by Ron J.

Two CMOS Based Vehicle Anti-Hijack Alarms -  Automobile Alarm Circuits:  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 onthe circuit will trip.  After a few minutes delaywhen the thief is at a safe distancethe alarm will sound and the engine will fail.  The second circuit is a modification of the firstoffering enhanced protection in many more situations. __ Designed by Ron J.

Two Simple Circuit Relay Based Motorcycle Alarms -  Motorcycle Alarm Circuits:  These are twoeasy to buildrelay-based alarms.  You can use them to protect your motorcyclebut they have many more applications.  If you use relays with 6-volt coilsthey'll protect your "Classic Bike".  Both alarms are very small.  The completed boards occupy about half a cubic-inch8 cc.  The standby current is zeroso they won't drain your battery. __ Designed by Ron J.

Two-Terminal Temperature-to-Current Thermometer Suitable for Use at the End of Long Wire Runs -  Adding the LT3092 to a thermistor kit along with three 0.1% accuracy resistors and one final trim, a very accurate 2-terminal temperature-to-current converter can be built.  This circuit measures 700μA operating current at 0°C, dropping by 2μA every degree until 100°C, at which point the current measures 500μA.  The obvious __ Linear Technology/Analog Devices App Note, Oct 26th 2010

Two-Tone Siren using One 4093 IC -  This circuit is intended for children fun, and can be installed on bicycles, battery powered cars and motorcycles, but also on models and various games and toys.  With SW1 positioned as shown in the circuit diagram, the typical dual-tone sound of Police or Fire-brigade cars is generated, by the oscillation of IC1A and IC1B gates. __ Red Free Circuits

Two-Zone Burglar Alarm -  Multi-Zone Burglar Alarm Circuits:  This two-zone alarm has automatic exit, entry and siren cut-off 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 minutesand prevent the alarm from activating a second time. __ 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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