Door alarm for Fridge

This circuit will help you to save your electricity bill.  Incase if you leave the fridge door open more than twenty seconds. The circuit consumes very little current as it can operates by a 3 volts battery. You can enclose this whole circuit in a small box and keep inside the fridge.

R2 is a photo resistor. Normally photo resister has a low resistance but when you close the fridge door, with the darkness the photo resister’s resistance will go high. When you open the door fridge lamp will light and photo resister’s resistance goes down.

 Then the IC1 start its action. You can set the preset according to your wish but in this circuit it is set for 20 seconds delay. After 20 seconds the piezo starts beeps until you close the door.

Remember not to place the alarm box inside the freezer try to place it near the lamp.

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Touch Sensitive Alarm Circuit Diagram

Description

                Circuit showing a Touch Sensitive Alarm .Here i have used bc 548 transistor for switching and bc 107 for sound generation
.You need a power supply

Click here to view the power supply circuit diagram

Components Required

 Resistor

            680R ,100 K

 Transistor

             BC 548, BC 107 - 2

Loud Speaker

Copper plate

Source by : http://www.electronics-circuits.in/2012/03/touch-sensitive-alarm-circuit-diagram.html#more

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Simple Shadow Detector Alarm

This is also known as Sun up alarm, in this circuit you can set the LDR’s sensitivity by 100k potentiometer, you can set it with any lamp around your room (tube light, bulb, LED etc) by varrying the 100k potentiometer. We can also control the buzzer time by 1M potentiometer 
 
You can Enhance this project and set the sensitivity of the LDR with a lazer light and keep it on the way of any door circuit at one side and lazer at other side of the door and a then you can make this project to buzz as soon as some one enters in a room 
 
I personally set this project in my room with sensitivity of tube light and whenever i came in and turn my room’s tube light on

rookieelectronics

Parts Required: 100k & 1M potentiometers  10k, 1Mx(3), 47k 0.1mF, 0.01mF & 10mF LDR BC337 transistor Beeper/Buzzer 9v Battery Supply

   Circuit Diagram:

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Mains Supply Failure Alarm

Whenever AC mains supply fails, this circuit alerts you by sounding an alarm. It also provides a backup light to help you find your way to the torch or the generator key in the dark. The circuit is powered directly by a 9V PP3/6F22 compact battery. Pressing of switch S1 provides the 9V power supply to the circuit. A red LED (LED2), in conjunction with zener diode ZD1 (6V), is used to indicate the battery power level.

Resistor R9 limits the operating current (and hence the brightness) of LED2. When the battery voltage is 9V, LED2 glows with full intensity. As the battery voltage goes below 8V, the intensity of LED2 decreases and it glows very dimly. LED2 goes off when the battery voltage goes below 7.5V. Initially, in standby state, both the LEDs are off and the buzzer does not sound. The 230V AC mains is directly fed to mains-voltage detection optocoupler IC MCT2E (IC1) via resistors R1, R2 and R3, bridge rectifier BR1 and capacitor C1.

Illumination of the LED inside optocoupler IC1 activates its internal phototransistor and clock input pin 12 of IC2 (connected to 9V via N/C contact of relay RL1) is pulled low. Note that only one monostable of dual-monostable multivibrator IC CD4538 (IC2) is used here. When mains goes off, IC2 is triggered after a short duration determined by components C1, R4 and C3. Output pin 10 of IC2 goes high to forward bias relay driver transistor T1 via resistor R7.

Circuit diagram:

Mains Supply Failure Alarm Circuit Diagram

Relay RL1 energises to activate the piezo buzzer via its N/O contact for the time-out period of the monostable multivibrator (approximately 17 minutes). At the same time, the N/C contact removes the positive supply to resistor R4. The time-out period of the monostable multivibrator is determined by R5 and C2. Simultaneously, output pin 9 of IC2 goes low and pnp transistor T2 gets forward biased to light up the white LED (LED1).

Light provided by this back-up LED is sufficient to search the torch or generator key. During the mono time-out period, the circuit can be switched off by opening switch S1. The ‘on’ period of the monostable multivibrator may be changed by changing the value of resistor R5 or capacitor C2. If mains doesn’t resume when the ‘on’ period of the monostable lapses, the timer is retriggered after a short delay determined by resistor R4 and C3.

 

 

Source: EFY Mag

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Motorcycle Alarm Circuit

Circuit Notes

Any number of normally open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. While at least one switch remains closed, the siren will sound. About two minutes after the switches have been opened again, the alarm will reset. How long it takes to switch off depends on the characteristics of the actual components used. But, up to a point, you can adjust the time to suit your requirements by changing the value of C1.

The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Without its terminal blocks, the board is small. Ideally, you should try to find a siren with enough spare space inside to accommodate it. Fit a 1-amp in-line fuse close to the power source. This protects the wiring. Instead of using a key-switch you can use a hidden switch; or you could use the normally closed contacts of a small relay. Wire the relay coil so that it is energized while the ignition is on. Then every time you turn the ignition off, the alarm will set itself.

When its not sounding, the circuit uses virtually no current. This should make it useful in other circumstances. For example, powered by dry batteries and with the relay and siren voltages to suit, it could be fitted inside a computer or anything else thats in danger of being picked up and carried away. The low standby current and automatic reset means that for this sort of application an external on/off switch may not be necessary. Electronics Circuit Application

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Burglar Alarm Circuit

This is a very useful circuit for you all.This is actually little bit different circuit.Because this circuit has used little bit advance knowledge.This circuit operates with 9V.You can fix this circuit for a door(SW1).Its ok though people use this door.But if some one keep opened it more than 30 seconds the alarm begins to ring.only users should know they should closed the door before 30 seconds.Think different way and use this in different way.

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Morning Alarm Circuit Diagram based LDR

This LDR based alarm can be used as get up alarm. The Alarm turns on in the morning automatically and turns off only when manually switched off ,so you will have to get up. It is a simple LDR based light sensor circuit.

LDR or Light Dependent Resistor is a kind of variable resistor and its resistance depends on the intensity of light falling on it. In complete dark, its resistance is as high as 1 Meg Ohm, but it reduces to 100 ohms or less in full light. So it is an ideal device to use as light switch. Sensitivity of LDR depends on its size also. Commonly available sizes are 3mm, 5mm, 10mm etc. But costly types with greater sensitivity are also available.

When the circuit is place in dark, near the window, LDR fails to conduct and T1 will not get base bias. So it remains off and buzzer will be silent. When the sunlight falls on LDR, IN the morning, LDR conducts and provides base bias to T1. T1 then conducts to activate the buzzer. Capacitor C1 is provided for the clean switching of T1. T1 will conduct only when C1 is charged fully. This prevents chirping sound during light transition.You can use an easily available Music buzzer to get melody tone.

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How to build Personal alarm

Small, portable, anti-bag-snatching unit
Also suitable for doors and windows control

Circuit diagram

• R1 330K 1/4W Resistor
• R2 100R 1/4W Resistor
• C1 10nF 63V Polyester or Ceramic Capacitor
• C2 100µF 25V Electrolytic Capacitor
• Q1 BC547 45V 100mA NPN Transistor
• Q2 BC327 45V 800mA PNP Transistor
• SW1 Reed Switch and small magnet (See Notes)
• SPKR 8 Ohm Loudspeaker (See Notes)
• B1 3V Battery (two A or AA cells wired in series etc.)

Device purpose:

This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord. If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts oscillating and the loudspeaker emits a loud alarm sound. The device can be reverse connected, i.e. the box can be placed in a pocket and the cord connected to the bag. This device can be very useful in signalling the opening of a door or window: place the box on the frame and the magnet on the movable part in a way that magnet and reed switch are very close when the door or window is closed.

Circuit operation:

A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a small loudspeaker. Low part-count and 3V battery supply enable a very compact construction.

Notes:

• The loudspeaker can be any type, its dimensions are limited only by the box that will contain it.
• An on-off switch is unnecessary because the stand-by current drawing is less than 20µA.
• Current consumption when the alarm is sounding is about 100mA.
• If the circuit is used as anti-bag-snatching, SW1 can be replaced by a 3.5mm mono Jack socket and the magnet by a 3.5mm. mono Jack plug with its internal leads shorted. The Jack plug will be connected with the tiny cord etc.
• Do not supply this circuit with voltages exceeding 4.5V: it will not work and Q2 could be damaged. In any case a 3V supply is the best compromise

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Simple Light Sensor Alarm circuit with NE555

This circuit despatched out an alarm when its LDR sensor is uncovered to mild with the aid of solar or lamp. A 555 astable multivibrator was once used here which despatched sign a tone of about 1kHz upon detecting mild.The sensor when exposed by gentle fulls the circuit and makes the 555 oscillate at about 1kHz with transistor to power current.

The sensor can be shown within the circuit diagram. It has to positioned making an angle of about 30 – 45 stages to the bottom.

Sensitivity will also be modify with P1.  This makes the solar gentle to float thru it to the bottom and stops the alarm from happening as a outcome of the saved mild on the sensor.

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Cheap Bicycle Alarm Schematics Circuit

The writer needed an extraordinarily low cost and simple alarm for some of hellos possessions, one of theses hellos electrically assisted bicycle. This alarm is in accordance with a low-cost window alarm, which has a time-switch delivered to it with a 1-minute time-out. The output  pulse of the 555 substitutes the reed change in the window alarm. The 555 is brought about through a sensor mounted near the entrance  wheel, in combination with a magnet that's mounted on the spokes. This sensor and the magnet have been taken from an affordable bicycle laptop. 

Circuit diagram :

Cheap Bicycle Alarm Circuit Diagram

The entrance wheel of the bicycle is stored unlocked, so that the reed  change closes momentarily when the wheel flips. This  set offs the 555, which in turn prompts the window alarm. The circuit around the 555 takes very little present and can  be powered by means of the batteries in the window alarm.  There  is just sufficient room  left inside the enclosure of the window  alarm to mount the time-switch inside of it. 

The result is a very low-cost, compact device, with handiest a single cable going to the reed swap on the front wheel. And the noise this factor produces is solely unbelievable! After about one minute the noise stops and the alarm goes again into standby mode. The bicycle alarm should be established in an not noticeable place, this type ofs underneath the saddle, inside of a (large) entrance light, in the battery compartment, etc.

Hopefully the alarm scares any attainable thief away, or at least it makes other individuals of the common public aware that one thing isnt moderately proper. 

Caution. The installation and use of this circuit could also be subject to prison restrictions for your country, state or area.

Author : Gerard Seuren

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