Simple Small Portable Alarm Circuit

The system involves positioning a small magnet near the stalk switch SW1, which is connected to the hand or garments of the individual carrying the bag via a tiny cable. Due to the compact nature of the circuit, it can be housed in a small plastic enclosure. The magnetic field will lose contact with the switch when the bag is snatched. This action will cause the circuit to oscillate, activating a loud alarm sound from the loudspeaker. Alternatively, the unit can be placed in a pocket while the cable is connected to the bag, creating a reverse connection method. The high-efficiency oscillator is formed by wiring a corresponding pair of transistors that drive a small 8 Ohm loudspeaker directly. The assembly is compact, powered by a 3 V battery (B1) with a minimal number of components. Any loudspeaker may be used, but its size is limited by the enclosure dimensions. The standby current is less than 20 µA, eliminating the need for an ON/OFF switch. When the alarm sounds, the circuit consumes approximately 100 mA. To enhance the circuit's functionality, a 3.5 mm mono jack can replace the switch, while a 3.5 mm mono jack plug with its internal leads shorted can substitute for the magnet. The tiny cable connects to the jack plug. The voltage supplied to the circuit should not exceed 4.5 V to prevent damage to transistor Q2. For safety, a 3 V supply using two AA cells in series is recommended. Personal alarms are rapidly becoming a popular segment in the self-defense market due to their loudness and portability. They can take the form of keychains, compact flashlights, levered hooks, or wristbands, and are designed to deter attackers by surprising them with a high-pitched alarm that attracts attention. The device can also signal the opening of a window or door by placing the enclosure on the frame and the magnetic field on the movable part, ensuring proximity between the switch and the magnet when the window or door is closed. The BC547 is an NPN small-signal transistor designed for general-purpose switching and amplification, characterized by reasonable voltage handling, low current consumption, and three gain options. The BC327 is a PNP general-purpose transistor in a TO-92 package, suitable for basic switching and amplification applications, particularly in audio amplification stages due to its high current capability (up to 500 mA) and low voltage rating (maximum 45 V).

The circuit operates on a principle that combines magnetism and electronic switching to create a personal alarm system. When the magnet is in proximity to the stalk switch SW1, the circuit remains inactive. However, if the magnet is removed—such as when an assailant attempts to snatch the bag—the stalk switch is opened, triggering the oscillator circuit. This oscillator is constructed using a pair of transistors, typically the BC547 for the NPN configuration and the BC327 for the PNP configuration, which work in tandem to amplify the signal and drive the loudspeaker.

The oscillator generates a square wave signal that is fed into the loudspeaker, producing a loud sound that serves as a deterrent. The choice of an 8 Ohm loudspeaker is optimal for this application, as it matches the output capabilities of the transistor pair. The use of a 3 V battery allows for prolonged operation, given the low standby current, and the circuit's design minimizes component count, enhancing reliability and reducing potential points of failure.

In addition to the basic alarm functionality, the circuit can be adapted for various applications, such as securing windows and doors. By placing the magnetic switch configuration on a window frame, the device can alert the user if the window is opened, providing an additional layer of security. The compact design makes it suitable for integration into various personal items, ensuring ease of use and accessibility. The inclusion of a 3.5 mm jack allows for flexible configurations, enabling users to customize their alarm system according to their needs. This versatility, combined with the circuit's effectiveness, positions it as a valuable tool in personal safety and security.The system of using this circuit is positioning a little magnet close to the stalk switch SW1 while being connected to the hand or garments of the individual holding the sack with the use of a tiny cable. Since the circuit is tiny, it can be put in a tiny plastic box. The magnetic field will definitely loose its contact with the splint change the moment the bag is snatched instantly. The circuit will definitely start oscillating if SW1 starts and will certainly produce a loud alarm sound from the loudspeaker. Alternatively, the unit can be placed in a pocket while the cable is linked to the bag, to develop a reverse approach of connection.

The high efficiency oscillator is made up by electrical wiring a corresponding transistor-pair that will definitely drive a small 8 Ohm loudspeaker directly. A very compact assembly is the result of 3 V electric battery quantity B1 and reasonable count of parts made use of.

Any kind of loudspeaker can be made use of yet the measurement is directed by the box where it will be positioned. Considering that the standby current being drawn is less than 20 uA, it is not required to include an ON/OFF switch.

A existing of around ONE HUNDRED mA is consumed by the circuit when the alarm system is sounding. To make the circuit a lot more appealing, a 3. 5 mm mono jack can be made use of as substitute for the switch while a 3. 55 mm mono jack plug with its interior leads shorted can be made use of in place of the magnet. The tiny cable will certainly be connected to the jack plug. The voltage used to provide this circuit should not go over 4. 5 V since the transistor Q2 could acquire ruined. To be on the risk-free side, it is suggested to utilize a 3 V supply with two AA cells wired in series. The personal alerts are one of the fastest growing portions in the self protection sector today because they are exceptionally loud as well as beneficial to hold.

It could be available in the kind of essential chains, rich torches, levered hook, or hand band. It is utilized for scaring off an attacker by unexpected them with high pitch alarm that may attract attention of others in the spot. The opening of a window or doorway may give a signaling procedure utilizing this gadget which can be done by putting the box on the frame as well as the magnetic field on the transferable part.

In this way, the splint switch as well as the magnetic field will definitely be extremely close when the window or doorway is closed. BC547 isNPN tiny signal transistors produced for basic application changing and boosting due to its reasonable voltage, low current as well as 3 different gain options BC327 is a PNP basic purpose transistor in a TO-92 bundle, made use of for basic purpose changing and amp applications which is suitable for AF driver periods and inexpensive power outcome stages of audio amps due to its attributes of high current at FIVE HUNDRED mA maximum and inexpensive voltage at 45 V optimum

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