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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.

Micro Power Over-Temperature Alarm -  The circuit is powered for years by a single 3 volt lithium battery.  It sounds an alarm when the temperature exceeds a certain point.  With some minor changes the circuit could also be configured for an under temperature (freeze) alarm.  The circuit uses a. . . Circuit by Dave Johnson P.E.-June, 2000

Monitors Pump Motor -  This circuit solves this problem in a novel way.  It clips on the outside of the pump motor’s power cable and provides a transistor switch closure whenever the circuit detects current flowing to the motor.  The circuit draws so little current that a small lithium cell will power the circuit for yearsCircuit Solution by David A. Johnson P.E.-November, 2004

Next-Generation 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 . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2001

Over-Temperature Micro-Power Alarm -  The circuit is powered for years by a single 3 volt lithium battery.  It sounds an alarm when the temperature exceeds a certain point.  With some minor changes the circuit could also be configured for an under temperature (freeze) alarm.  The circuit uses a . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

Power Loss Beeper -  For some medical equipment it is important for an operator 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. . . Circuit by David Johnson P.E.-March, 1999

Pump Motor Monitor -  This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on.  It is designed to detect the motor current using a small inductor placed on the outside of the motor’s power cable.  No direct wire contact is needed. . . Circuit by David Johnson P.E.-November, 2004

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

N/O: N/C 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 

Next-Generation 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 . . . Hobby Circuit designed by Dave Johnson P.E.-October, 2001

Night Lamp with Alarm -  This circuit automatically turns on a night lamp when bedroom light is switched off.  The lamp remains ‘on’ until the light sensor senses daylight in the morning.  A super-bright white LED is used as the night lamp.  It gives bright and cool light in the room.  When the sensor detects the daylight in the morning, a melodious __ Designed by Popescu Marian

Noise-Level Alarm -  Noise is a serious environmental problem that affects us in our daily life.  There is scientific evidence supporting that noise exposure can cause hearing loss, hypertension, heart disease, annoyance, sleep disturbance __ Electronics Projects for You

Novel buzzer using a relay & transformer -  This novel buzzer circuit uses a relay in series with a small audio transformer and speaker.  When the switch is pressed, the relay will operate via the transformer primary and closed relay contact.  As soon as the relay operates the normally closed contact will open, removing power from the relay, the contacts close and the sequence repeats, all very quickly __ Designed by Andy Collison

One Time Only Alarm -  This alarm is designed to sound its Siren only once.  That iswhen the alarm is activatedthe 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 __ Designed by Ron J.

One-button lock provides high security -  03/04/99 EDN-Design Ideas (contains several designs, scroll to find this one)   Figure 1 is the block diagram of an easily programmed, single-button combination lock.  You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button.  The circuit uses inexpensive CMOS logic.  The retriggerable timer, T1, locks out entries made after the T1 code-entry window, thereby greatly enhancing security.  The circuit in Figure 2 operates as follows: The Schmitt-trigger quad NAND gate, IC1, debounces the code-entry switch and, with the aid of simple analog circuitry, produces separate outputs for activation times of less than and more than 0.3 sec.  These outputs connect to the select gate, IC5 __ Circuit Design by Maxwell Strange, Fulton, MD

One-IC Design Monitors Ajar Doors -  This design senses an ajar door and, if the situation isn’t corrected within 20 sec, sounds a beeping alarm. __ Circuit Design by Fred Hicks, General Electric Co, Louisville, KY

One-Time-Only Burglar Alarm -  Multi-Zone Burglar Alarm Circuits:  When this alarm is activated its Siren will sound oncefor 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, there's also a range of Expansion Modules.  These will allow you to add any number of Instant Zones, Tamper Zones and Personal Attack Zones to your system. __ Designed by Ron J.

One-Time-Only Motorcycle Alarm -  Motorcycle Alarm Circuits:  This is a "one-time-only" alarmwith an LED activation indicator.  If the bike is movedthe siren will sound for about a minute.  Then it will switch offand remain off.  It won't activate a second time.  It can't be activated againuntil the next time the alarm is set. __ Designed by Ron J.

Open Fridge-Door Alarm -  It beeps if the fridge door is left open for too long or hasn't closed properly, to stop food from spoiling.  There are lots of other uses as well.  A refrigerator or freezer door that is left open or ajar may cause the food contents to spoil.  In some cases, the internal temperature of the fridge or freezer will be maintained if the refrigeration system can cope with the open door __ Learning Electronics

Open-door Alarm prevents accidental Defrosts -  1-Feb-07 EDN-Design Ideas __ Circuit helps save a lab freezer or temperature chamber's contents __ Circuit Design by Tom Lyons Fisher, Juniata College, Huntingdon, PA

Opened Window or Door Alarm -  Economical circuit of an electronic alarm, notifies you when your door or window is open, is presented here.  This circuit wired around the Quad 2-input NAND Schmitt trigger IC 4093 (IC1) can be powered from a standard 9V battery.  Here, a normally-closed (N/C) push switch (S1) is used to monitor the door/window activity.  For __ Designed by T.K. Hareendran

Optical Smoke Detector -  This optical smoke detector uses a low-cost, readily-available, slotted, through-scan, infrared photo-switch.  When smoke is detected, the relay energises to activate the audio/visual warning alarm.  Fig.1 shows the circuit of the __ Electronics Projects for You

Oscillating Output Improves System Security -  02/06/03 EDN-Design Ideas Filter allows comparison of noisy signalsMany electronic-control systems have digital outputs that use transistors.  One method of improving the security in these outputs is to use an oscillating signal to represent a logic-high state instead of a fixed voltage level(Figure 1).  This type of signal, a dynamic variable, can drive the circuit shown in Figure 2 __ Circuit Design by Jorge Marcos and Ana Gómez, University of Vigo, Vigo, Spain

Oscillator/Reference Oven Temperature Regulation -  The LTC2990 is used to monitor system temperatures, voltages and currents.  Through the I2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC.  The internal 10ppm/°C reference minimizes the number of supporting __ Linear Technology/Analog Devices App Note, Mar 16th 2011

Overheat Detector Alarm Switch -  At the heart of this overhead detector (fire alarm) circuit is a precision integrated temperature sensor type LM35 (IC1), which provides an accurately linear and directly proportional output in mV, over the zero to +155 degrees C temperature range.  This can be used as part of fire smoke detectors but do not use it as a home __ Designed by Popescu Marian

Over-Temperature Alarm -  This circuit can be used as a warning device which triggers an alarm whenever the temperature exceeds a preset level.  It can also be used as a door-alert or general warning __ Electronics Projects for You

Over-Temperature Micro-Power Alarm -  The circuit is powered for years by a single 3 volt lithium battery.  It sounds an alarm when the temperature exceeds a certain point.  With some minor changes the circuit could also be configured for an under temperature (freeze) alarm.  The circuit uses a . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

Panic Alarm -  If you feel threatened or need emergency assistance, simply activate this alarm.  It will catch the attention of others for immediate help.  The alarm will sound for three minutes and then __ Electronics Projects for You

PC Temperture Alarm -  This circuit uses a temperature sensor to detect the temperature inside the PC and generates an alarm if the temperature exceeds a pre-set limit. __ Electronics Projects for You

PC wakeup on call -  You want to access your PC at home when you are away? And you want to have it switched off to save power and to be sure that it is not hacked in the mean time? This is your solution.  This little piece of electronics interfaces one of the analog phone outputs of your VoIP/DSL router to the power-on pin of your PC.  Due to the use of a transformer and an optical coupler, everything is completely insulated and lightning protected.  Give yourself a call from whereever you are and after 3 rings your PC will power on.  What if your PC hangs up while you are away? Let it ring 7 times and you PC will hard switch off and is ready for a reboot. __ Designed by Herbert Dingfelder

PC Watcher Turn On & you’ll hear the Alarm -  This little PC Watcher circuit will help you to prevent unauthorised access to your personal computer.  After construction on a small piece of veroborad, enclose the whole circuit in a tamper proof plastic box and connect its input to a vacant USB port at the rear of your Desktop PC, using a standard USB cable.  Now hide the unit __ Designed by T.K. Hareendran

PC-Controlled Burglar Alarm SystE - M -  Fancy a full-featured alarm control panel with dialler capabilities? This one is PC-programmed and controlled and can handle up to eight zones.  The PC only needs to be powered up for arming and disarming, or you can use an optional keypad. __ SiliconChip

Perimeter Monitor -  Using a single cable such as speaker wire or doorbell cable, this circuit can be remotely positioned, for example, at the bottom of a garden or garage, and used to detect all sound in that area.  The cable can be buried in a hosepipe or duct and is concealed out of sight.  The mic is an ordinary dynamic mic insert __  Designed by Andy Collison

Personal Alarm -  Small, portable, anti-bag-snatching unit; Also suitable for doors and windows control __ Contact: Flavio Dellepiane, fladello @ tin.it

Photodiode Alarm -  This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area.  The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode.  When the beam path breaks, alarm will be triggered.  The circuit uses a PN Photodiode in the reverse bias mode to detect light __ Designed by D Mohankumar

Photodiode-Based Fire Detector -  This ultra-sensitive fire sensor protects your electronic devices like computer and television set.  It uses a photodiode as the fire sensor and sounds an alarm immediately on sensing a spark or __ Electronics Projects for You

Photoelectric Smoke Detector -  This photoelectric smoke detector circuit uses one LED and 2 LDRs to detect the smoke and sound an alarm.  The LM1801 IC is the best choice for this circuit because we need a few external components and is used in almost any smoke alarm.  The whole photoelectric smoke detector circuit is powered from the 220V mains supply.  D1 __ Designed by Popescu Marian

PIC Projects: Alarm Clock-Cum-Temperature Indicator -  Although many circuits for digital clocks have been published in Electronics For You, this circuit is a PIC microcontroller (MCU) based easy-to-construct gadget, which combines a clock with a temperature indicator __ Electronics Projects for You

PIC12F635 Based Door Alarm SystE - M -  Now you can build your own simple door alarm security system using a tiny microcontroller chip PIC12F635! The circuit is nothing but an aural alert unit, which raises a warning tone when the concerned door is opened by someone.  You can install this unit in your front/back door as a security alarm to deter burglars and __ Designed by T.K. Hareendran

PIC12F675 Microcontroller Based Security Alarm -  Crime in general is still on the rise, and having a security alarm installed is no longer a perquisite of the wealthy! Here is a simple and compact security alarm system to protect your home/shop and valuables.  The circuit is built around a tiny microcontroller chip PIC12F675.  Besides, a ready-made Passive Infrared (PIR) __ Designed by T.K. Hareendran

PIC16F84 Alarm Clock -  This is an alarm clock I built.  It was very effective during the sort time I used it, because I programmed it to play a very annoying tune through a speaker.  I actualy started to wake up before the alarm went of, so other people int he house didn't wake up from the anoying pitches it played.  The Jal sourcecode is available on my download page Features * Timekeeping

Piezoelectric Device used for Motion Alarm -  An inexpensive piezo wafer is used to detect vibration and when the vibration is sufficient a switch is activated . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Piezoelectric Heat Sensor -  Here is an Ultrasensitive Heat Sensor to monitor high temperature in Electronic devices.  It can be placed inside the electronic gadget that usually generates heat during its operation.  The circuit also functions as a sensitive Fire Alarm.  This heat sensor uses the piezoelectric property to sense heat.  The sensor element is the __ Designed by D Mohankumar

Platinum RTD Digitizer Accurate within 1° Over 0°C to 100°C -  Platinum RTD Value Is Linearly Converted to Period by LTC1799.  Logic and Second LTC1799 Clock Digitize Period into Output Data Bursts.  Bootstrapping Pin Capacitance is used to Permit Remotely Located Sensor. __ Linear Technology/Analog Devices App Note, Apr 7th 2010

Platinum RTD Signal Conditioner with Curvature Correction -  The left stage forms a stable precision current source by establishing the reference voltage across a precision resistor, and about half of this current passes through the sensor.  The right opamp provides an amplification of the resistance difference between the sensor and a fixed precision resistor to generate a temperature __ Linear Technology/Analog Devices App Note, Jun 21, 2011

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

 


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