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Alarm Circuits Page 2
Alarms:  #-C          D-G         H-O         P-R         S       
T-U       V-Z

Last Updated on: Tuesday, April 01, 2014 04:28 AM
 

Circuits Designed by Dave Johnson, P.E.

  • Doggie Water Dispenser Alarm - I have two Beagle dogs.  They drink a lot of water; they go through about 3 gallons a week.  They have two water dispensers.  One is on the inside and second unit on the outside of my house.  Often, I forget to fill one of their two jugs and discover them completely empty.  I do worry that my dogs might get dehydrated if I ever forget to fill both of their containers.  To help prevent this, I decided to design and build a battery powered alarm system which would monitor the level of water in the jugs and sound an alarm when the water level dropped below a certain volume....(circuit of the week designed by David Johnson, P.E.)

  • DOORKNOB ALARM
    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 placed around the inside doorknob of a wood door. Anyone grabbing the knob from the outside is detected by the electrical capacitance change that occurs from the human hand contact between the knob and the box. Almost all of the commercial devices sold use a more expensive and power consuming radio frequency circuit approach to detect the capacitance change. But, a very inexpensive and micro power technique can also work. This circuit schematic should dramatically reduce the cost of the device and allows it to operate for many years from one set of batteries. Also see Completed Project  by Matthew C. Ruschmann
  • Door Knock Beeper
    In some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door from the outside.  The circuit is powered by a 9v battery, which should provide years of service.  An on/off switch allows the device to be turned off if desired...
  • Earthquake Alarm Circuit
    Geophones are dandy motion sensors.  They are metal cans containing a powerful magnet, suspended with springs inside a coil of wire.  The magnet functions as a floating mass.  The slightest vertical motion of the device causes the coil to move relative to the magnet.  This induces a small voltage in the wire coil...
  • Fake Car Alarm Light
    Whenever the car’s ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system. (added 7/06)
  • Freezer Over-Temperature Alarm
    This circuit turns on a beeper whenever the inside temperature of a freezer is greater then 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.   (added 12/04)
  • Freezing Temperature Alarm
    This circuit turns on a beeper whenever the outside air temperature is less 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.   (added 12/04)

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
DayLight Alarm -  The circuit presented here wakes you up with a loud alarm at the break of the daylight. Once again the 555 timer is used here. It is working as an astable multivibrator at a frequency of about 1kHz…. [Radioland.nt.au]
DC/DC Converter operates from Phone Line -  15-Jan-98 Issue of EDN DC/DC converters for use inside the telephone handset require operation from the high-source-impedance phone line. Additionally, the CCITT specifications call for maximum on-hook power consumption of 25 mA. The dc/dc converter in Figure 1 is 70%-efficient at an input power of 25 mA, providing 5V at 3.4 mA. Controlled, low-peak switch.... [Design Idea by Gary Shockey, Linear Technology Corp, Milpitas, CA]
Digital Combination Lock -  A multiple input combination loack using CMOS counter IC's. Flexibility and code change is allowed by changing output connections.
Digital Electronic Lock circuitdb -  The digital lock shown below uses 4 common logic ICs to allow controlling a relay by entering a 4 digit number on a keypad. The first 4 outputs from the CD4017 decade counter (pins 3,2,4,7) are gated....(added 05/07)
Doggie Water Dispenser Alarm - I have two Beagle dogs.  They drink a lot of water; they go through about 3 gallons a week.  They have two water dispensers.  One is on the inside and second unit on the outside of my house.  Often, I forget to fill one of their two jugs and discover them completely empty.  I do worry that my dogs might get dehydrated if I ever forget to fill both of their containers.  To help prevent this, I decided to design and build a battery powered alarm system which would monitor the level of water in the jugs and sound an alarm when the water level dropped below a certain volume....(circuit of the week designed by David Johnson, P.E.)
Door Alarm -  Hangs up on the door-handle.  Beeps when someone touches the door-handle from outside (added 3/05)
Door Knock Beeper -  In some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door from the outside.  The circuit is powered by a 9v battery, which should provide years of service.  An on/off switch allows the device to be turned off if desired.... [Designed by David A. Johnson]
Door/window sensor resists tampering -  01/21/99 Issue of EDN  The simple, inexpensive circuit in Figure 1 detects a failure (or deliberate tampering] on lines connected to normally closed switch sensors. For example, common door interlocks and door/window sensors consist of normally open or normally closed magnetic reed switches. Depending....Page includes several designs.  Scroll to find this one.... [Design Idea by Paul Nocella, Q Research, Brookline, NH]
Doorknob Alarm -  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 placed around the inside doorknob of a wood door. Anyone grabbing the knob from the outside is detected by the electrical capacitance change that occurs from the human hand contact between the knob and the box. Almost all of the commercial devices sold use a more expensive and power consuming radio frequency circuit approach to detect the capacitance change. But, a very inexpensive and micro power technique can also work.  This circuit schematic should dramatically reduce the cost of the device and allows it to operate for many years from one set of batteries. …. [Hobby Corner Circuit by Dave Johnson]
Doorknob Proximity Alarm -  Reverse engineered circuit diagram of a popular retail doorknob alarm. It contains a small transmitter and the doorknob acts as an antenna so it will not work on a metal door. When a person comes close to the doorknob this loads down the oscillator and the alarm sounds. The proximity sensor circuitry is perfectly capable of driving 74HCT series CMOS logic instead of the noise maker IC's shown in the circuit diagram.... [Reverse engineered schematic by Stepan Novotill]
Doorknob touch alarm -  The project was originally intended as a present for my brother’s dorm room, but a bad capacitor and the lack of a proper oscilloscope caused delays. It has not made it off the breadboard, and it probably will not until his next semester. The circuit contains a few basic elements, an flip-flop based oscillator, a set of delays, a flip-flop as a sensor, and the audible alarm.  (project added 6/07)
Dozen Small CMOS Alarm Circuits -  This is a selection of small self-contained alarm circuits. They have a very low standby current; and are suitable for battery operation. Some are triggered by normally-open and normally-closed switches. Some react to changes in light or temperature. The result is a variety of output times and patterns.  (Circuit design added 04/05/06)
Dummy alarm -  Schematic only, no circuit description
Dummy Alarm -  This project makes a superbright LED flash briefly once every 5 seconds to imitate the indicator light of a real alarm. The circuit is designed to use very little current to prolong battery life so that it can be left on permanently.  This is a simple project, ideal for a beginner.... (circuit added 06/07/08) [Designed by John Hewes]
Earthquake Alarm Circuit -  Geophones are dandy motion sensors.  They are metal cans containing a powerful magnet, suspended with springs inside a coil of wire.  The magnet functions as a floating mass.  The slightest vertical motion of the device causes the coil to move relative to the magnet. This induces a small voltage in the wire coil.... [Hobby Corner Circuit by Dave Johnson]
Earthquake Detector -  Circuit designed by Jochen Leug
Electric Field Disturbance Monitor -  This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor.  The system can detect human and animal motion by the electric fields they disturb. ….
Electric Field Disturbance Monitor-2 -  This schematic is the motion discriminator alarm and battery monitor sections of the field monitor that is discussed in more detail a Electric Field Disturbance Monitor. (this link is off-site) …. [Designed by David A. Johnson]
Electronic Buzzer -  This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC. The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on. The frequency can be changed by varying the 10K resistor.  (added 10/05)
Electronic buzzer -  This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC. The 555 is setup as an astable multivibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on. The frequency can be changed by varying the 10K resistor.... [Radioland.nt.au]
Electronic Canary Doorbell -  This circuit is a modified "Hartley Oscillator" with a couple extra parts.  T1, the LT700 (Tony van Roon's or equivalent, is a small center tapped (Tony van Roon's ct) audio transformer with an impedance of 1000 ohms at 1000 hertz.  The secondary of this transformer has an impedance of 8 ohms.  Usually noted as 1K:8 ct.  I tried a couple other models like the red and green types (Tony van Roon's taken out of a $5 made-in-china am pocket radio) and they both work good.  You may have to adjust the caps to get the sound.... [Tony van Roon's circuit]
Electronic Card Lock System -  (electronic Circuit / Schematic added 10/04)
Electronic Combination Lock -  This circuit is very basic to build. To open a the lock which is connected to the K1 Load you must press each momentary switch in the correct sequence. The sequence used in this circuit is S1,S2,S3,S4. If any of the other switches are pressed the circuit will reset and you will need to start over.... [Randy Linscott, designer]
Electronic door codelock PIC16F84 -  (circuit diagram added 2/07) [Peter Jakab, Electrical Engineer, Engineer of Informatics]
Electronic Door Release -  This circuit is designed to operate an electrical door-release mechanism, but it will have other applications. When you enter the four-digit code of your choice, the relay will energize for a preset time period. Use the relay contacts to power the release mechanism. The standby current is virtually zero, so battery power is a realistic option. [Circuit designed by Ron J.]
Electronic Keypad -  The IC is a quad 2 input "AND" gate, a CMOS 4081. These gates only produce a HIGH output, when BOTH the inputs are HIGH. When the key wired to 'E' is pressed, current through R1 and D1 switchs Q5 on.The relay energises; and Q5 is 'latched on' by R8. Thus, the Alarm is set by pressing a single key,say one of the two non-numeric symbols.... [Ron J.'s circuit
Electronic Lock -  The digital lock shown below uses 4 common logic ICs to allow controlling a relay by entering a 4 digit number on a keypad. The first 4 outputs from the CD4017 decade counter (pins 3,2,4,7) are gated.… [Posted by Jospfh]
Emergency Light & Alarm -  Powered by2-AA NI-CD batteries Four switchable options (added 6/06)
Emergency Siren Simulator -  This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail.  (Circuit design added 08/08)
Enhanced 4 Digit Alarm Keypad -  (circuit diagram added 1/07)
Enhanced 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….(Circuit design added 08/08/08)
Enhanced 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....(diagram added 6/03)
Enhanced Shed/ Garage Alarm  -  This is an enhanced version of the simple Garage/Shed Alarm. The Entry and Exit delays have been increased to about 30-seconds, and I've added a timed Siren cut-off and automatic Reset. I've also replaced the LED with an entry Buzzer. These enhancements mean that the new version will have a much wider application. Photo (Circuit design added 04/05/06)
Ethernet Based Security System -   [Site is underconstruction right now]
Everything-that-moves alarm -  A crucial failing of proximity detectors is their unreliable and tricky nature.  This is where they are used to detect humans, not to speak of smaller living beings. One common approach is to detect.... (electronic design added 10/06)
Expandable Multi-Zone Modular Burglar Alarm -  This circuit features automatic Exit and Entry delays and a timed Bell Cut-off. It has provision for both normally-closed and normally-open contacts, and a 24-hour Personal Attack/Tamper zone. By using the Expansion Modules, you can add as many zones as you require; some or all of which may be the inertia (shock) sensor type.... [Circuit by Ron. J.]
Expandable SCR Based Burglar Alarm -  This is a simple SCR based burglar alarm circuit. Its features include automatic Exit and Entry delays, together with a timed Bell Cut-off and Reset. The basic alarm has a single zone.  This will be adequate in many situations. However, the modular design means that you can add as many zones as you like to the system. Details of a Four-Zone expansion module are provided... [Circuit by Ron. J.]
Expandable Transistor Based Burglar Alarm -  This transistor based alarm features automatic Exit and Entry delays, together with a timed Bell Cut-off and system Reset. Along with the Exit/Entry zone, the basic alarm board has one Instant Zone.  This will be adequate in many situations. However, the modular design means that it's easy to add as many zones as you like to the system. Details of a Four-Zone expansion module are provided.... [Circuit by Ron. J.]
Factory Siren -  This circuit produces a sound similar to a factory siren.  It makes use of a 555 timer IC used as an astable multivibrator of a center frequency of about 300Hz. The frequency is controlled by the pin 5 of the IC. When the supply is switched ON, the capacitor charges slowly and this alters the voltage at pin 5 of the IC hence....(added 05/07) [Radioland.nt.au]
Fake Car Alarm Light -  Whenever the car’s ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system+O860 [Designed by David A. Johnson]
Fire Alarm -  This circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire. When this smoke passes between a bulb and an LDR, the amount of light falling on the LDR decreases.  This causes the resistance of LDR to increase and the voltage at the base of the transistor  [Radioland.nt.au]
Four Digit Keypad -  (diagram added 6/03)
Four Small Transistor Alarm Circuits -  This is a selection of simple self-contained transistor based alarm circuits, complete with photographs. They are designed….(Circuit design added 04/05/06)
Four-Digit Alarm Keypad -  Pressing a single key on the keypad, will energize the relay. Entering a four-digit code of your choice, will de-energize it. The circuit was designed to control the Modular Burglar Alarm System -....(added 05/07)
Freezer Over-Temperature Alarm -  This electronic hobby 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 hobby circuit.  The average 9ua current is so low that the battery should last for many years.... [Hobby Corner Circuit by Dave Johnson]
Freezing Temperature Alarm -  This circuit turns on a beeper whenever the outside air temperature is less 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.... [Hobby Corner Circuit by Dave Johnson]
Fridge door Alarm -  Beeps if you leave open the door over 20 seconds.  3V battery operation, simple circuitry.  (circuit added 9/04)
Frost Alarm (Andy Collinson) -  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. (added 2/06)
Fuse Blown Indicator -  a simple way to see if a fuse has blown without removing it from its holder (added 4/02)
Fuse Monitor/Alarm -  a simple way to see if a fuse has blown without removing it from its holder (added 4/02)
Gate alarm circuit -  Figure 1 represents a cheap and simple Gate Alarm, that is intended to run off a small universal AC-DC power supply….(diagram added 2/07)


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



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