200V Live Wire Scanner
When you hold the sensor (metallic conductor or copper wire) close to the live wire, electric field from mains activates the circuit. As the input impedance of the CMOS IC is high, the electric field induced in the sensor is sufficient to clock it. The output obtained at pin 11 of CD4017 drives the LED. Flashing of the LED (LED2) indicates the presence of mains, while LED1 indicates that the scanner is active.
The circuit can be used to find stray leakage from electrical appliances like fans, mixers, refrigerators, etc. It can be easily assembled on any general-purpose board or the discrete components can be directly soldered on the IC.
A 9V PP3 battery powers the circuit. If you use a mains adaptor, make sure that it is well regulated and isolated; otherwise, even the stray electric field from mains transformer will clock the circuit.
Use insulated wire as sensor to avoid risk of exposure to live AC mains.
The article was first published in August 2005 and has recently been updated.