MELODY's BURGLAR ALARM: Physics Science Working Model-Project  (Multicolor)

The circuit is basically an audio oscillator. The fencing alarm circuit described below doesn’t give any sounds when the wire loop is connected, i.e. the base of T-1 is shorted to its emitter. Hence the base current cannot flow. And when the loop is broken the current startflowing through T-1 and circuit starts oscillator sounding an alarm. In the circuit, the Transistor T-1 acts as a pre- amp Transistor T-2 as the power amplifier to operate speaker.Capacitor C1 and Resistor R-2 provides feedback oscillation to the Transistor’s T-1 base to sustain the oscillator circuit. Since both the transistor are silicon type, a very little current is drawn from the battery in the alert mode. COMPONENTS USED