This is a CMOS IC (CD4033)
based circuit which can be used to detect presence of mains AC voltage without
any electrical contact with the conductor carrying AC current/voltage. Thus
it can be used to detect mains AC voltage without removing the insulation from
the conductor. Just take it in the vicinity of the conductor and it would detect
presence of AC voltage. If AC voltage is not present, the display would randomly
show any digit (0 through 9) permanently. If mains supply is available in the
conductor, the electric field would be induced into the sensing probe. Since
IC used is CMOS type, its input impedance is extremely high and thus the induced
voltage is sufficient to clock the counter IC. Thus display count advances rapidly
from 0 to 9 and then repeats itself. This is the indication for presence of
mains supply. Display stops advancing when the unit is taken away from the mains
carrying conductor. For compactness, a 9-volt PP3 battery may be used for supply
to the gadget
