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Personal alarm schematic

2016-02-19 09:03  
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This article is a personal alarm schematic presentation. Master the principle is very effective method is to combine text read schematics. The personal alarm is a small, portable, anti-bags grab units. Also applies to doors and windows control. A complementary pair of transistors connected as an efficient oscillator, directly driving a small speaker. Low part count and 3 v battery supply allows for a very compact structure. Speakers may be any type, and its size is limited only by the enclosing box. A switch is unnecessary, because the standby current is less than 20μa painting. Current consumer warning sound when approximately 100 ma. If the circuit  is used as anti-bag to grab, SW1 can be written as a 3.5 mm mono Jack socket and the magnet through a 3.5 mm. mono plug has its internal cause a short circuit. This plug will be connected to a small rope. This circuit does not supply voltage exceeds 4.5 v: it will not work and Q2 may be damaged. In any case, 3 v supply is the best compromise.

Circuit diagram:

Personal Alarm


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.)




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