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How to build Live-line Detector

2018-11-10 12:06  
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Detects the presence of a live mains conductor

Minimum parts counting

Circuit diagram

Live-line Detector-Circuit diagram


C1 100nF 63V Polyester or Ceramic CapacitorD1 Red LED (any type)IC1 4017 Decade counter with 10 decoded outputs ICP1 SPST PushbuttonB1 3V Battery (two 1.5V AA or AAA cells in series etc.)Sensing probe__3 to 15 cm. long, stiff insulated piece of wire

Circuit operation:

If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10.When remote from a live line, the unit stops counting, the LED resulting permanently off.


Sensitivity can be varied using a more or less long sensing probe.Due to 3V operation, the LED's current limiting resistor can be omitted.

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