# Non-contact voltage antenna range

How to change the range of antenna for non-contact voltage detection? For example I would like to detect 220 VAC at 1 cm, 2 cm or 5 cm. Can I make these changes with potentiometer? I attached my circuit TNX

if I find 220 volts at a distance of 10 centimeters in normal mode, I want to change the distance between 1 cm to 10 cm with a 2 key or one potentiometer or one keys . what should I do ?

1) The "10 cm Plastic wire" is confusing, what should be used is an isolated wire so that it is IMPOSSIBLE to make (conductive) contact to anything and especially mains voltages (220 VAC).

2) this circuit actually work on capacitive coupling between 220 VAC, that "Antenna" and also capacitive coupling between you (your hand) holding the circuit. This capacitive coupling causes small AC currents to flow and the circuit detects those.

3) To improve sensitivity, you could increase the capacitive coupling. This can be done by not using a wire as the antenna but a small metal plate of 2 x 2 cm for example and mounted at the inside of a plastic box. Like the wire it needs to be isolated so the plastic box is needed. Then also place a second metal plate (or something else conductive) inside the box on the side that will be closest to your hand.

So: it is important to remember that the circuit including everything connected to it should be inside a plastic box. That's the only way to make it safe to use to detect 220 V AC. If you ignore this advice, you're risking your life!

Last remark: this is a simple circuit, I believe it can work provided there is enough capacitive coupling to the 220 V AC. But you might not be able to reach the 5 cm, for that you might need a more advanced design.

• Am I crazy or is that really decade counter? Also, it is funny that "more advanced designs" on J-FETS are often simpler than this peculiar creation – Maple Sep 21 '18 at 7:54
• @Maple Indeed the 4017 is a decade counter. It's suppose to start counting if there is enough signal at the CLK input and then the LED will flash. with "more advanced" I meant something that would amplify the signal somewhat instead of relying on a floating CMOS input (which I regard as "fishy" and unpredictable). – Bimpelrekkie Sep 21 '18 at 8:03
• I suspect that amplification required for 5 cm will make it even less reliable, since even clothes movement will set it off. Maybe something like adaptive threshold followed by bandgap for mains frequency is needed – Maple Sep 21 '18 at 8:17
• @Maple followed by bandgap for mains frequency You mean Bandpass filter. A Bandgap circuit is what I use to make a (temperature stable) DC reference voltage. – Bimpelrekkie Sep 21 '18 at 8:37
• Oops, yes, of course. It's 5AM here, I do not know what I am typing anymore – Maple Sep 21 '18 at 8:42

Your schematic may work but is misleading because it does not describe the actual functional circuit with internal ESD clamp diodes and inductive wire and capacitive coupling plastic insulated wires for a plug or probe.

In reality, you are AC coupled to an E-field > 9Vpp depending on mutual coupling L of probe length and plastic thickness and gap for capacitance. The input is not biased until some ac stray signal is clamped. The ESD diodes clamp and centre or self-bias the ac signal and drive the counter so that the Johnson counter can flash at 5 or 6 Hz (/10) briefly for 1/10 duty cycle.

simulate this circuit – Schematic created using CircuitLab

estimated ballpark values.

• hi . tnx for Your description . In fact, the antenna used in my circuit is inside a plastic box, and my circuit antenna is an 345 UH .in reality my problem is the distance between the detection circuit. For example, if I find 220 volts at a distance of 10 centimeters in normal mode, I want to change the distance between 1 cm to 10 cm with a 2 key or one potansiometr. – amirr Sep 21 '18 at 9:04
• You can a ferrite rod or flat core antenna tuned near 50/60 Hz with a load cap. – Tony Stewart Sunnyskyguy EE75 Sep 21 '18 at 17:35
• imbalanced ESD leakage will keep the detector from doing any detection – analogsystemsrf Sep 22 '18 at 4:42
• Maybe, I should have included 33M feedback with imbalance shunt in design to supply self biased input so a buffered input can amplify E fields – Tony Stewart Sunnyskyguy EE75 Sep 22 '18 at 4:51