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

 

Last Updated: December 07, 2017 02:03 PM

 

Circuits Designed by Dave Johnson, P.E.

Freeze Alarm -  I chose an accurate thermistor from Keystone as the temperature sensor for this circuit.  This device has a very specific resistance at a particular temperature.  According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water.  The thermistor is wired into a simple bridge circuit, which uses 1% resistors.  The bridge is connected to a very low power voltage comparator.  The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value.  At zero degrees C the voltage at the non-inverting input of the comparator exceedsCircuit Solution by Dave Johnson P.E.-May, 2006

Freezer Over-Temperature Alarm -  This circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.. . . Circuit by Dave Johnson P.E.-November, 2014

Freezing Temperature Alarm -  The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.. . . Circuit by David Johnson P.E.-November, 2014

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

 
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Freeze Alarm -  I chose an accurate thermistor from Keystone as the temperature sensor for this circuit.  This device has a very specific resistance at a particular temperature.  According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water.  The thermistor is wired into a simple bridge circuit, which uses 1% resistors.  The bridge is connected to a very low power voltage comparator.  The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value.  At zero degrees C the voltage at the non-inverting input of the comparator exceedsCircuit Solution by Dave Johnson P.E.-May, 2006

Freezer Over-Temperature Alarm -  This circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.. . . Circuit by Dave Johnson P.E.-November, 2014

Freezing Temperature Alarm -  The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.. . . Circuit by David Johnson P.E.-November, 2014

Fridge Alarm-Version 1 -  activated by the light in a fridge or freezer.  Sounds an alarm if the door is left open too long __ Contact: P. Townshend EduTek Ltd

Fridge Alarm-Version 2 -  this 10a MOSFET driver will power most small to medium power dc motors up to 24v __ Contact: P. Townshend EduTek Ltd

Fridge Door Alarm -  This fridge door alarm is using a 3V battery supply should be placed (in a small box) in the fridge near the lamp or close to the opening.  With the door closed the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1.  When a beam of light enters from the opening, __ Designed by Popescu Marian

Fridge door Alarm -  Beeps if you leave open the door over 20 seconds; 3V battery operation, simple circuitry __ Contact: Flavio Dellepiane, fladello @ tin.it

Fridge door Alarm (2nd Version) -  Alternative version of the popular circuit; 3V battery supplyStill operating at 1.3V __ Contact: Flavio Dellepiane, fladello @ tin.it

Fridge-Door Open 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. __ SiliconChip

Fridge-Door Open 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

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

Frost Alarm -  The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius.  A suitable bead type thermistor is found in the Maplin catalogue.  The 100k pot allows this circuit to trigger over a wide range of temperatures.  A slight amount of hysteresis is provided by inclusion of the 270k resistor.  This prevents relay chatter when temperature is near the switching threshold of this circuit __ Designed by Andy Collison

Full-Bridge Amplification using a Resistor Arrays to Provide Precise Matching in Excitation Amplifier -  This example provide excitation using resistor arrays to produce precise gain.  The circuit is configured to provide 10V and 5V excitation to the bridge, producing a common mode voltage at the input to the LTC2430/LTC2431 of 2.5V, maximizing the AC input range for applications where induced 60Hz could reach amplitudes up __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Full-Bridge Amplification using a Single Amplifier -  This example shows a single amplifier being used to produce single-ended gain.  This topology is best used in applications where the gain setting resistor can be made to match the temperature coefficient of the strain gauges.  If the bridge is composed of precision resistors, with only one or two variable elements, the reference __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Full-Bridge Amplification using Autozero Amplifiers to Reduce Input Referred Noise -  This circuit shows an example of a simple amplification scheme.  This example produces a differential output with a common mode voltage of 2.5V, as determined by the bridge.  The use of a true three amplifier instrumentation amplifier is not necessary, as the LTC2430/LTC2431 have common mode rejection far beyond that of most __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Fuse Monitor/Alarm -  a simple way to see if a fuse has blown without removing it from its holder __ Designed by Andy Collison

Fuse-Cum-Power Failure Indicator -  This fuse-cum-power failure indicator comprises an LED (LED1), light-dependent resistor (LDR1), inverter circuit and two timer circuits built around IC NE555.  LDR1 and preset VR1 form a voltage divider at the __ Electronics Projects for You

Gag Bomb Countdown Timer -  18-Jul-14 -Design News:   I created this Hollywood movie-style gag bomb that doubles as an alarm clock and a countdown timer.  This is a fun project that you can build in a day or two.  It is made using an 8051 microcontroller.  The project can be easily done with other microcontrollers or an Arduino, or you can even hack an __   Gadget Freak-Case #259

Gamma-photon Detector -  04/24/03  EDN-Design Ideas LED driver delivers constant luminosityThe circuit of Figure 1 includes a PIN photodiode that detects individual photons of gamma radiation.  The reverse bias on the photodiode sometimes creates a depletion region.  When such a ph __ Circuit Design by Bruce Denmark, Maxim Integrated Products, Sunnyvale, CA

Gas Leak Detector -  Here is a gas leak detector circuit that detects the leakage of LPG gas and alerts the user through audio-visual indications.  The circuit operates off a 9V PP3 battery.  Zener diode ZD1 is used to convert 9V into 5V DC to drive the gas sensor module.  The gas leakage circuit uses the SEN-1327 gas sensor module from RhydoLABZ. __ Designed by Popescu Marian

Gas Leakage Alarm -  LPG gas is supplied in pressurised steel cylinders.  As this gas is heavier than air, when it leaks from a cylinder it flows along floor and tends to settle in low __ Electronics Projects for You

Gate alarm -  Figure 1 represents a cheap and simple Gate Alarm, that is intended to run off a small universal AC-DC power supply. __ Designed by Andy Collison

Gated alarm -  Sometimes the need arises for a simple, gated, pulsed alarm.  The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-done for simplicity.  While it does not offer the most powerful output, it is likely to be adequate for many applications.  A dual CMOS timer IC type 7556 is used for the purpose, __ Learning Electronics

General purpose Alarm using discrete transistors -  The alarm may be used for a variety of applications, such as frost monitor, room temperature monitor, and so on.  In the quiescent state, the circuit draws a current of only a few microamperes, so that, in theory at least, a 9 V dry battery (PP3, 6AM6, MN1604, 6LR61) should last for up to ten years.  Such a tiny current is not possible when ICs are used, and the circuit is therefore a discrete design.  Every four seconds a measuring bridge, __ Learning Electronics

Glass Break Alarm -  This circuit can be used for sounding an alarm to detect the breaking of a glass window by an intruder, even when the intruder ensures there is no sound of the __ Electronics Projects for You

Glass Break Detector -  Glass Break Detector can be designed with 3 types of implementations in mind: Standalone, wireless connectivity and Fixed/Wired Connectivity.  The first two implementations are battery operated.  The functional block diagram of the glass break detector is divided into 3 sub-blocks: the sensing block, the processor and the communication interface blocks.  When implementing a basic standalone type of glass break detector, the processor and the communication interface are not needed

Graphical Alarm Clock -  Software: The software is written in a state machine manner.  Here are the states: (the state numbers were chosen randomly) State 1: Show the power up graphics State 2: Main time/date display State 50: Main menu State 60: Set the clock State 61: Set __ Designed by Atmel ATmega32 Part 1

GSM Home Security Alarm System with Arduino -  This project deals with the design & development of a theft control system for home, which is being used to prevent/control any theft attempt.  The developed system makes use of an embedded system (comprises an open hardware microcontroller and a gsm modem) based on Global System for Mobile communication (GSM) technology. __ Designed by T.K. Hareendran

Gunn diode proximity Detector -  Schematic only __ Designed by va3iul

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


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