Try this single IC circuit for Non contact detection of current in live wires. It can detect the presence of AC from a distance of 30cm or more without touching the bare points of live wire. It is ideal to detect cable break, switch board faults, earth leakage etc. The circuit detects the e.m.f (called AC hum) present around the live wire when the electricity passes. Only a single IC CD4033 can do the trick.
CD4033 is the Johnson counter IC used in digital display circuits and driving the 7 segment display. Its input is too sensitive and readily accepts the e.m.f pulses and treats the 50Hz AC pulses as clock pulses and gives decoded outputs which can be used to light an LED or drive a buzzer. The Counter advances one by one with each positive Clock signal in its input when the clock inhibit pin is held low. In normal operation, the Reset and Clock enable pins are held at ground and the Ripple blanking input is connected to ground or a more significant count stage. The counter then advances one count on each negative to positive transition of the clock pulse. The counter resets when the reset pin is high and this results all 7 outputs low. The reset pin must be returned to ground to restart the count again.
Assemble the circuit on a common PCB and enclose in case. Case of a Marker pen is a good choice. Use a Pin or multimeter probe as antenna. A 12 volt mini battery (one used in car remote) will make the circuit compact enough to enclose in the case.
Caution: Do not touch the antenna to bare points of live wire, plugs, switches etc. Since it is a non contact tester, the LED blinks even when the tester is 30 cm away from the wire.
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