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Contact less AC line tester Using NPN Transistor BC547


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  1. Transformerless Power Supply Module:
    • A transformerless power supply module is used to power the circuit safely. It typically includes capacitors and resistors for voltage reduction and filtering.
  2. NPN Transistor (BC547):
    • The NPN transistor is used as a switch. When an AC voltage is detected, the transistor allows current to flow, turning on the indicator LED.
  3. LED (Indicator):
    • An LED is connected to the collector of the NPN transistor. When the transistor is turned on, the LED lights up, indicating the presence of AC voltage.
  4. Phototransistor or Photodiode:
    • A phototransistor or photodiode is used as an optical sensor. It is placed near the live wire but without direct contact. The presence of AC voltage induces a small current in the phototransistor or photodiode, activating the transistor.

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