Saturday, June 15, 2024

Contactless AC Mains Voltage Detector

This is a CMOS IC (CD4033) based contactless AC mains voltage detector circuit which can be used to detect presence of AC mains 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.

This is a circuit for an AC mains voltage detector that has an insulated sensing probe of length between 5 cm to 10 cm. When this sensing probe is taken in vicinity of AC mains the numbers in the display change repeatedly from 0 to 9 if it detects AC.

Contactless AC mains voltage detector circuit


If AC voltage is not present, the display would randomlys Show any digit (0 through9) 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.

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  1. Thanks for helping me understand more about contactless AC mains voltage detector. I didn’t know that this circuit can help a detector that has an insulated sensing probe. You mentioned that this probe has to be between 5 cm and 10 cm, and I’m kind of interested to know more about the different types of insulated sensing probes there are and when they should be used.


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