Live Wire Scanner. Design Trick 11

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.


Get more details for CD4033 Design from this link

2 responses to “Live Wire Scanner. Design Trick 11

  1. Mohon Sir,
    Thanking you for your circuit ‘live wire scaner’. I just made it and it is woking fine(LED blinking) on a live wire from a distance of 6-10 inches. But I am facing some problem which needs your suggetion.
    Many times led is continiously glowing in full or dim condition like faulse triggering.
    In case of any live wire under wall pluster (consealed) or plastic casing or any obstruction between the wire and the antena, the circuit stops working.
    I am using red led (100R is correct?) , HCF4033BE ic, 9 volt pack battery (as 12v car remote battery not available with me now).
    The ic is slightly hot after using of 5 minutes (perhaps due to continious glowing of led)
    Waiting for your valuable suggesion/modification

    • Hello
      No fault in your circuit. IC is CMOS IC works at 5 to 12 volts. If it is too hot, reduce the voltage to 6 volts.LED is blinking occasionally , because the input is getting emf from the atmosphere especially the high emf near TV, Fan, Induction cooker, Transformer, computer etc. As you said, concealed wiring detection may be a problem if the cable is very deep in the wall and the PVC tubing is strong.No modification is necessary. To share the output load, you can use 7 LEDs one in each output with a single resistor for all LEDs. If low voltage, low current LED is used, increase the value of series resistor to IK. You can also use a common cathode 7 segment display.