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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Anti Theft Security For Car Audios

This small circuit, based on popular CMOS NAND chip CD4093, can be effectively used for protecting your expensive car audio system against theft. When 12V DC from the car battery is applied to the gadget (as indicated by LED1) through switch S1, the circuit goes into standby mode. LED inside optocoupler IC1 is lit as its cathode terminal is grounded via the car audio (amplifier) body. As a result, the output at pin 3 of gate N1 goes low and disables the rest of the circuit.

Whenever an attempt is made to remove the car audio from its mounting by cutting its connecting wires, the optocoupler immediately turns off, as its LED cathode terminal is hanging. As a result, the oscillator circuit built around gates N2 and N3 is enabled and it controls the ‘on’/‘off’ timings of the relay via transistor T2. (Relay contacts can be used to energise an emergency beeper, indicator, car horns, etc, as desired.)

Anti-Theft Security For Car Audios Circuit diagram:

Different values of capacitor C2 give different ‘on’/‘off’ timings for relay RL1 to be ‘on’/‘off’. With 100µF we get approximately 5 seconds as ‘on’ and 5 seconds as ‘off’ time. Gate N4, with its associated components, forms a self-testing circuit. Normally, both of its inputs are in ‘high’ state. However, when one switches off the ignition key, the supply to the car audio is also disconnected.

Thus the output of gate N4 jumps to a ‘high’ state and it provides a differentiated short pulse to forward bias transistor T1 for a short duration. (The combination of capacitor C1 and resistor R5 acts as the differentiating circuit.)As a result, buzzer in the collector terminal of T1 beeps for a short duration to announce that to announce that the security circuit is intact. This ‘on’ period of buzzer can be varied by changing the values of capacitor C1 and/or resistor R5. After construction, fix the LED and buzzer in dashboard as per your requirement and hide switch S1 in a suitable location. Then connect lead A to the body of car stereo (not to the body of vehicle) and lead B to its positive lead terminal. Take power supply for the circuit from the car battery directly.

Caution.

• This design is meant for car audios with negative ground only.

Author:T.K  Hareendran Copyright: Circuit Ideas

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Powerful Security Siren

Simple circuit - No ICs required, 12V Battery operation

This circuit was requested by several correspondents. Its purpose was to obtain more power than the siren circuit already available on this website (One-IC two-tones Siren) and to avoid the use of ICs. A complementary transistor pair (Q2 & Q3) is wired as a high efficiency oscillator, directly driving the loudspeaker. Q1 ensures a full charge of C2 when power is applied to the circuit. Pressing on P1, C2 gradually discharges through R8: the circuit starts oscillating at a low frequency that increases slowly until a high steady tone is reached and kept indefinitely. When P1 is released, the output tone frequency decreases slowly as C2 is charged to the battery positive voltage through R6 and the Base-Emitter junction of Q2. When C2 is fully charged the circuit stops oscillating, reaching a stand-by status.

 Circuit Diagram:

Powerful Security Siren Circuit Diagram

Parts:

P1 = SPST Pushbutton Operating Switch
R1 = 1K
R2 = 10K
R3 = 1K
R4 = 220R
R5 = 10K
R6 = 220K
R7 = 22K
R8 = 100K
C1 = 22uF-25V
C2 = 22uF-25V
C3 = 10nF-63V
C4 = 47uF-25V
Q1 = BC557
Q2 = BC557
Q3 = BC337
B1 = 12V Battery
SW1 = SPST Toggle or Slide Main Switch
SPKR = 8 Ohms Loudspeaker

  Notes:

• A good sized loudspeaker will ensure a better and powerful output tone.
• As stand-by current drawing is zero, SW1 can be omitted and B1 wired directly to the circuit.
• Maximum current drawing at full output is about 200mA.

Source : www.redcircuits.com

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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

Read more →