The Non-Contact Voltage Detector remains one of my favorite Weekend Projects of all time frankly because it’s easy to build and fun to play with (just watch the YouTube video we produced for the project to see what I mean).
I have a few ‘pen testers’ designed for automotive and home applications, and the Non-Contact Voltage Detector was just as reliable in home tests. It comes with the added benefit of being completely DIY, made with just a few common components that you might already have laying around your workshop. The original design by Dean Segovis called for a small enclosure, but you can just as easily port the design to any enclosure you choose – pen, enclosure, or some other form factor.
And if you don’t want to spare the time to solder the circuit on perfboard and fit everything in an enclosure, try prototyping the circuit on breadboard. It’s quick and will still reward you with that same “Aha!” when you compare live to non-live wires. Check it out:
I could have used fewer wires to jump from transistor-to-transistor, but I opted instead to separate each component to make the junctions more clear. The silver box at the top is the ‘pad’ of conductive metal I used in place of copper. It should be noted this layout is without a momentary switch. As soon as you plug in the battery’s wires the circuit is operating and it will remain on until you either unplug the wires or remove the battery. See the original circuit schematic for comparison. Now watch how sensitive – and accurate – the Detector is. In the following videos the same wire is plugged in and then not plugged in. Watch the feedback given by the LED:
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All this took was a breadboard, 3 resistors, 3 2N3904 transistors, some wire, a conductive plate, a red LED, and a 9V battery. Watch the full video below to see how to perfboard the circuit and fit it all inside an enclosure. And have fun with this Weekend Project sensing static charge in the world around you!