Finding broken wire inside wall or over insulator is very difficult and here is the simple solution to find the broken wire, here we have used only transistors to identify the broken wire location. By using simple broken wire detector we can identify the presence of current flow, if there is no current flow then buzzer and LED becomes off.
Normal wire can be used as antenna to pickup electromagnetic force (EMF) from the current flowing wire. Three stage Transistors act as amplifiers and strengthens detected signal from current flowing wire and makes Buzzer to produce beep sound and LED to blink. If there is no current flow then Buzzer and LED stays in turn OFF position.
Construction & Working
The circuit is a simple but effective AC current detector. When alternating current (AC) flows through a nearby wire, it generates emf in the spiral wire, and forward biasing the base-emitter junction of the first transistor Q1 in the circuit and consequently driving Q1 , and transfers current from its collector to its emitter. This current drives a second transistor, Q2, which in turn allows current to flow from its collector to its emitter. Q2 is connected directly to the base of Q3, the third transistor, it is forward-biased Q3 and drives current through it. This completes the circuit in series for the buzzer, LED and resistor.
When Q3 turns ON, the buzzer emits a sound and the LED illuminates, producing an audible and visual signal of AC current flow detection in nearby wire. This circuit design demonstrates the cascade effect of a transistor, where a transistor one works following other transistor, and finally makes the output work.
This circuit uses the induced voltage in the spiral wire to detect the presence of AC current in a nearby wire. When AC current is detected, the buzzer and LEDs activate, providing visual and audible indications of the AC signal. If there is an open or broken connection, the buzzer and LED will remain in the OFF position.
BC547 (NPN) pin details
When the antenna wire placed near current flowing wire it will pickup EMF signal and after amplification by three transistors Buzzer and LED makes indication. If the wire broken then there will be no EMF and hence there is no indication from buzzer and LED.