Security Alarm

Thwart any attempt of burglary in your house using this alarm circuit. When someone opens the door of your room, it sounds an alarm intermittently and flashes light as well. The circuit can also be used as an audio/visual alarm in case of fire or other emergency by momentarily pressing switch S3.

The circuit (refer Fig.1) is built around transformer X1, a standard bar magnet, reed switch S2, timer IC NE555 (IC1), opto-coupler IC MOC3020 (IC2), TRIAC BT136 and a few discrete components. Timer IC1 is wired as an astable multi-vibrator whose reset pin 4 is controlled by the reed switch. The reed switch fitted in the door frame acts as the sensor. A magnet is fixed on the door panel close to the reed switch.

Fig.1: Simple Security Alarm Circuit Diagram :

The reed switch consists of a pair of contacts on ferrous metal sealed in a glass envelope. The contacts may be normally-open (which close when a magnetic field is present) or normally closed type (which open when a magnetic field is applied). A normally open- type reed switch is used here.

When the door is closed, reed switch S2 is in open state. When the door is opened, the bar magnet moves away from reed switch S2. As a result, reset pin 4 of IC NE555 goes high. The high output at pin 3 of IC1 enables IC2. Pin 4 of IC2 is connected to the gate of TRIAC1. When the door is opened, bulb B1 flashes and the bell sounds (provided switch S4 is closed) indicating that the door has been opened. Flashing of the bulb and the alarm continue until the door is closed.

Assemble the circuit on a general purpose PCB and enclose in a suitable cabinet. Connect the call bell at the back side and the bulb at the front side of the cabinet. Install the unit on the door of the room as shown in Fig.2.

Fig.2: Reed Switch Fitting in Door :



The circuit is powered by mains supply.

Source : http://www.ecircuitslab.com/2012/09/simple-security-alarm.html

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Fire alarm circuit

Many fire alarm circuits are presented here,but this time a new circuit using a thermistor and a timer to do the trick. The circuit is as simple and straight forward so that , it can be easily implemented.The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon is employed here for sensing the fire.


The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2. Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON. The larger the value of C1, the larger the positive bias applied to the base of transistor T1 (BC548). As the collector of T1 is coupled to the base of transistor T2, the transistor T2 provides a positive voltage to pin 4 (reset) of IC1 (NE555). Resistor R4 is selected s0 that NE555 keeps inactive in the absence of the positive voltage. Diode D1 stops discharging of capacitor C1 when the thermistor is in connection with the positive supply voltage cools out and provides a high resistance path. It also inhibits the forward biasing of transistor T1.

Notes.

* The circuit can be powered from a 6V battery or a 6V power supply.
* The thermistor can be mounted on a heat resistant material like mica to prevent it from damage due to excessive heat.
* The LED acts as an indication when the power supply is switched ON.

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Morning Alarm Circuit Diagram Using LDR

Description

          Circuit showing a morning alarm.Here we have used a switching transistor.When the sun rise up ldr is low resistance so the ldr is conduct and a positive volt coming to the base of the Q1 there for the transistor will switch.This time  the buzzer is ON . Adjust the preset control the intensity of light.Manually cut off the power.Are you interested please comment and join this site


Component Required

                Resistor  4.7k preset  , LDR

                Transistor   BC 548

                Buzzer




Source by : http://www.electronics-circuits.in/2012/01/morning-alarm.html

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Security Alarm

Thwart any attempt of burglary in your house using this alarm circuit. When someone opens the door of your room, it sounds an alarm intermittently and flashes light as well. The circuit can also be used as an audio/visual alarm in case of fire or other emergency by momentarily pressing switch S3.

The circuit (refer Fig.1) is built around transformer X1, a standard bar magnet, reed switch S2, timer IC NE555 (IC1), opto-coupler IC MOC3020 (IC2), TRIAC BT136 and a few discrete components. Timer IC1 is wired as an astable multi-vibrator whose reset pin 4 is controlled by the reed switch. The reed switch fitted in the door frame acts as the sensor. A magnet is fixed on the door panel close to the reed switch.

Fig.1: Simple Security Alarm Circuit Diagram :

The reed switch consists of a pair of contacts on ferrous metal sealed in a glass envelope. The contacts may be normally-open (which close when a magnetic field is present) or normally closed type (which open when a magnetic field is applied). A normally open- type reed switch is used here.

When the door is closed, reed switch S2 is in open state. When the door is opened, the bar magnet moves away from reed switch S2. As a result, reset pin 4 of IC NE555 goes high. The high output at pin 3 of IC1 enables IC2. Pin 4 of IC2 is connected to the gate of TRIAC1. When the door is opened, bulb B1 flashes and the bell sounds (provided switch S4 is closed) indicating that the door has been opened. Flashing of the bulb and the alarm continue until the door is closed.

Assemble the circuit on a general purpose PCB and enclose in a suitable cabinet. Connect the call bell at the back side and the bulb at the front side of the cabinet. Install the unit on the door of the room as shown in Fig.2.

Fig.2: Reed Switch Fitting in Door :



The circuit is powered by mains supply.

Source : http://www.ecircuitslab.com/2012/09/simple-security-alarm.html

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Drinking Water Alarm

The State Jal Boards supply water for limited duration in a day. Time of water supply is decided by the management and the public does not know the same. In such a situation, this water alarm circuit will save the people from long wait as it will inform them as soon as the water supply starts. At the heart of this circuit is a small water sensor. For fabricating this water sensor, you need two foils—an aluminium foil and a plastic foil. You can assemble the sensor by rolling aluminium and plastic foils in the shape of a concentric cylinder. Connect one end of the insulated flexible wire on the aluminium foil and the other end to resistor R2. Now mount this sensor inside the water tap such that water can flow through it uninterrupted. To complete the circuit, connect another wire from the junction of pins 2 and 6 of IC1 to the water pipeline or the water tap itself. The working of the circuit is simple.

Timer 555 is wired as an astable multivibrator. The multivibrator will work only when water flows through the water tap and completes the circuit connection. It oscillates at about 1 kHz. The output of the timer at pin 3 is connected to loudspeaker LS1 via capacitor C3. As soon as water starts flowing through the tap, the speaker starts sounding, which indicates resumption of water supply. It remains ‘on’ until you switch off the circuit with switch S1 or remove the sensor from the tap. The circuit works off a 9V battery supply. Assemble the circuit on any general-purpose PCB and house in a suitable cabinet. The water sensor is inserted into the water tap. Connect the lead coming out from the junction of 555 pins 2 and 6 to the body of the water tap. Use on/off switch S1 to power the circuit with the 9V PP3 battery.

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Long Range Cordless Burglar Alarm

This long-range cordless burglar alarm circuit makes use of a cordless telephone (CLT) unit with paging facility and a few low-cost discrete components. The circuit is so simple that even a novice can easily construct it without any difficulty. When the ‘page’ button on a CLT is pressed and held in that position, the handset starts beeping to indicate that somebody is calling. This function is used here to build the gadget. The system consists of three sub-assemblies:

   

1. Wireless beeper. The handset of the CLT.

2. Infrared transmitter. A number of IR transmitter circuits based on the well-known 555 chip have been published earlier in EFY. Just select one circuit with a modulating frequency of 36 to 38 kHz and assemble it on a veroboard. After that, enclose it in a proper cabinet. (EFY note. A typical IR transmitter circuit used during testing is shown in Fig. 1.)

 

3. Infrared receiver-cum-control unit. The circuit diagram of this unit is shown in Fig. 2. Front end of this block is Sharp’s GP1U561X integrated infrared re-ceiver module (or TK1836/ TSOP1836 from Temic/ Telefunken, etc). This mod-ule can demodulate 36kHz modulated IR beam to pro-duce an active-similar  ‘low’ output. You may also use any other module, provided it has an active-‘low’ output. The modulated IR beam from the transmitter is received by the receiver module and its output at pin 2 goes ‘low’. The rest of the circuit is in sleep mode as it does not get power for its operation. The SCR here plays the role of an electronic switch.

When the infrared beam is interrupted, the output of the receiver module goes ‘high’ to apply a forward bias to the base of transistor T1. As a result, the gate of SCR gets sufficient forward bias to conduct (and latch). The astable multivibrator built around IC1 starts working to control the  ‘on’/‘off’ relay timings. Diode D1 prevents the relay from latching and diode D2 works as a free-wheeling diode.

Normally open (N/O) contacts of the relay are used to close the  ‘page’ button contacts until the circuit is reset by pressing push-to-off switch S1 (N/C type). One may replace switch S1 with a key-lock switch to avoid its unauthorised operation. The astable circuit helps the hand-set user to distinguish between a normal paging call and an intrusion warning alarm.

After construction, fix the transmitter and receiver modules at opposite sides in the door frame as shown in Fig. 3. Carefully open the CLT and solder two wires to the  ‘page’ button terminals with their free ends connected to the relay contacts (N/O). Now your cordless burglar alarm with a wireless monitoring range of about 500 meters (actual range is based on the CLT’s paging range) is ready to detect an intruder.

EFY note. The author has success-fully tested his prototype with the following CLT makes:

• Panasonic KX-T 3611 BH (made in Japan)
• Panaphone WT-3990 (made in China)
• Citizen JRT-5400 (made in India)

Source:   http://www.ecircuitslab.com/2012/01/long-range-cordless-burglar-alarm.html

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Bicycle Anti Theft Alarm Circuit

I hate to suggest the specific application ‘bicycle’ because it may be use to protect many items from theft. This anti-theft alarm project is built around the inexpensive Measurement Specialties DT piezo film sensor. Every now and then everything seems to work out perfectly as in the Yin and Yang of the cosmos, and this is one of them.
It is simple, inexpensive and practical…


Anti-Theft Alarm Schematic

Bill of Material

anti-theft BOM.xls

Piezo sensor

I received this DT piezo film sensor as a sample years ago. It was attached to the application page via a round sticker. I never removed the sticker, but used it to attach #6 nut to increase inertia at the tip of the device—I could have experimented with other small masses, but this worked well from the git-go, so I left it that way. When the film is flexed, it produces a voltage at the terminals.
http://www.meas-spec.com/downloads/DT_Series.pdf
Initial experiments with the sensor were disappointing—I observed voltage and connected it to a charge pump type detector—yes, it functioned, but sensitivity was poor.
Single JFET transistor charge amplifier
Then I read up on charge amplifiers. One good discussion is “Signal Conditioning Piezoelectric Sensors” http://www.ti.com/lit/an/sloa033a/sloa033a.pdf
The paper discussed using FET input op amps in such a way that the sensor develops no voltage at the output terminals—only generates a current that is then amplified by the charge amplifier. This is important because the sensor has significant capacitance (e.g. 500pf) and any voltage generated by the sensor is swamped by this capacitance thus greatly attenuating the output voltage.
Then the wheels started turning—and I thought up a means of using a single JFET as a charge amplifier. This I bread boarded and tested—performance was phenomenal! The source feedback resistor doubles as a negative feedback device depending upon the position of the trim pot adjustment.
JFET selection

Unfortunately, the selection of TO-92 style JFETs is now limited, but the J111, J112 & J113 seem to be going strong. These three vary mainly in the Idss parameter (drain current with gate shorted to source). The J113 has a min Idss of 2mA that is best for our application because one goal is to minimize battery current. Since I did not have one of these devices on hand, I used an ancient MPF-106. I experimented with a total of (7) JFET devices, and only one would not work and that was because its Idss was so high that it turned itself fully on—I could have used this device by reducing the value of R3, but that would have increased battery drain. As it was, this stage consumed 160uA—similar to a low power op amp. NXP has the best J113 datasheet:
http://www.nxp.com/documents/data_sheet/J111_112_113_CNV.pdf
Charge pump detector
The charge pump detector is essentially the same as a cascade voltage doubler rectifier that is used for signal applications. It detects the peak to peak voltage of the AC input voltage waveform (minus the diode drops). In this circuit C2, C3, D1 & D2 perform this function. Additional sensitivity adjustment is possible via adjusting the value of C2. The value of C3 effects both attack and decay time.
Anti-Theft Alarm Oscillograph

Anti-Theft Alarm Protoboard

555 voltage threshold detector/pulse generator
You may recall that in a previous article, I did not recommend using pin 4 as a level detector.
http://electroschematics.com/7195/quirky-555-timer-reset-function/
However, I should have qualified it to allow the TLC555 CMOS device manufactured by TI. This device works well in this application with its low reset threshold (1.1V) and very high input impedance.
Wired as an astable multivibrator, the external components draw no additional current when in the reset condition. With a repetition rate of 2hZ, it gets maximum attention.
The TLC 555 is unable to source the required load of 28mA, so a 2N4401 provides the additional drive capability.
Battery operation
Idle current is about 300uA. Theft alarm mode current is about 28mA. This lends itself well to long 9V alkaline battery life. Furthermore, when the key switch is off, drain is zero.
Physical construction

Note this is something that I did not build, but this is how I would do it. The plastic box is indicated on the BOM. It may be attached to the bicycle frame via two cable ties that pass through holes in the box (either cover or box may be made stationary). If higher security is desired, cut slots in the box and use small stainless steel hose clamps with the buckle located inside the box where it is inaccessible—getting it all to fit may be a challenge. The LEDs are located on the left and right sides to obtain maximum attention—with the correct hole diameter, the LEDs are a press fit.
The key switch may be scavenged from an old desktop computer (if you can locate one with the key). They are also available on eBay at a very reasonable price (new)—used ones are expensive.
Glossary of undocumented words and idioms (for our ESL friends)
git-go –idiom, noun, variation of get-go –from the beginning or outset—although not indicated, I think that it was derived from the old animal handling (horse) phrase “giddy up”
wheels started turning –idiom, started to think

555 datasheet

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