Wiring schema blogs

Parts: 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.)



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.