Category Archives: Audio Circuits

Burglar Alarm Using NPN(BC548)And PNP(SK100) Transistor

The burglar alarm circuit shown here sounds an alarm when the wire loop is broken.The system is implemented by installing a sensing loop, which is basically a thin copper wire. This way, the loop is both invisible and brittle enough to break easily and initiate the alarm mechanism.At the time of an intrusion, the loop […]

SIMPLE AUDIO ALARM CIRCUIT USING BC547 AND S8550

Parts Required: Capacitors C1 – 0.02uF ceramic disc C2 – 1000uF, 12V or 25V Resistors (All 1/4Watts) R1 – 100K R2 – 2.2K R3 – 47E Transistors T1 – BC547 (NPN) T2 – S8550 (PNP) Loudspeaker – 8 ohms Battery – 9V This is a simple audio alarm which operates from 3 to 9 volts and […]