3 Replies Latest reply on Aug 12, 2014 6:25 AM by mcb1

    Non contact voltage detector questions?


      Hello all, my first post in this marvelous forum. (ben Heck pointed me here)


      I saw this video by make magazine http://makezine.com/projects/non-contact-voltage-detector/

      They make a non contact voltage detector from some transistors.

      I made one myself, and it works great.


      But the thing i am trying to find out is this.

      How to you increase the sensing distance? Could you add more transistors to increase the gain? (i tried with 1 more resitors (and a 10kresistor) but that dit not seem to work?

      How can i make this more directional?

      Does the antenna (the copperclad surface) have to be in copper? I tried brass and various others but the readings all came out pretty strange. (it can only detects from certain angles and such)

      I know there exists commercial appliances that can detect over several meters and also can swith into directional mode.

      AC Hotstick FAQ | High sensitivity voltage detector for emergency responders.


      So does anybody here know how this works? Or can point me to a place where i can read up "and understand" this? I am a Industrial designer by trade and sadly no electrical engineer


      All the best to all of you on this great day.





        • Re: Non contact voltage detector questions?


          Firstly what do you want it for.


          Sensing cables in walls would suggest a high sensitive device ...and funnily Shabaz has blogged about one here.

          DIY fun: Building a Mains Power Line Sniffer


          The electrical industry are using them more and more and again it depends on their use as to how sensitive they should be.

          If you work inside a switchboard you want to isolate which wire is live, but if you are only interested if power is at the wall outlet it can be more sensitive.


          They work by sensing the electric field (not the magnetic field) that is present around the wire when its energised with AC voltage.


          This might give some insight and the shortcomings of these tools ...they aren't the only method to ensure safety.



          One thing with any testing device is use the Prove, Test, Prove method.

          You Prove it with a known live source, then Test your cable/etc, then Prove again with a known live source.



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            • Re: Non contact voltage detector questions?

              Hi and thanks for answer.

              Forgot the obvious. I am trying to make some devices that help kids understand how different animals interact with the world. (in a simplified and abstracted way)

              One of the animals is the Platypus that senses electronic signals with its beak.


              So i want to make a device that can sense electronic singals from, computers, wires (230v) and other elecronic items. The item will not be used to check/fix or test exposed wires in any way. Best case scenario is if i could be able to "sense" signals from aprox 0-2 meters, and as directional as possible.


              Thnx for the link, reading it now.


              Mvh Anders

                • Re: Non contact voltage detector questions?


                  Excellent project.

                  Re the directional aspect. .. I've never tried at such low frequencies.

                  My first thought is to place the sensing antenna part inside a large tin can that is earthed (so it doesn't become the antenna)

                  search for "tin can wifi" and you'll get an idea.


                  The other thought is to use two coils with ferrite between and some form of difference measurement.

                  If the source is on one side only one detect it, and if its straight ahead both should be equal.


                  Whatever you make you'll need it filter out anything but 50/60 Hz.


                  The other option is a small transmitter on 433MHz and use a yagi type aerial and receiver ... its not quite the same as the 50hz but a similar principal.



                  1 of 1 people found this helpful