Mains Hum Detector / Static Electricity Detector





Introduction: Mains Hum Detector / Static Electricity Detector


This instructable is about a small and easy circuit which detects Mains Hum i.e you can detect where mains wires are located from outside of the wall.It also detects Static Electricity and also can be disguised as a Ghost Detector.

So,Just follow the steps and you can build it in no time!

Step 1: Equipments Required

This components are required:-


2. 1 X 5mm LED(Any Colour)

3. 1 X 220 Ohm Resistor

4. 1 X 100k Ohm Resistor

5. 1 X 1M Ohm Resistor

6. 6-8mm Thick Strong Copper Wire(Must be Rigid) For Antenna

7. Breadboard

8. A 9volt Battery

Step 2: Circuit Diagram

Here is the circuit diagram.

This project is based from

Step 3: Complete!

If you touch the antenna wire,the led's gonna glow.

Make sure you strip 1cm of the antenna.

You can make various antenna to increase the sensitivity.

Hope you enjoyed this instructable.

Please Comment if you have any problems.



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I accidently built this once using an NPN and PNP transistor Darlington pair,no resistors and a speaker.

What I really need is a circuit which will indicate whether a radio is turned on at around 160Mhz (153-173). This is for sonobuoys I'm using - I'm out in a boat and turn the transmitter on, and the only way to know if it's working is to radio back to the guy onshore with the receiver. It would be really useful to have a little gadget which lights up if its transmitting. Would some modification of this one work? I can just hold it against the case, doesn't have to be all that sensitive.

3 replies

The hum detector amplifies (50/60Hz) mains hum and while it will probably give some indication (as it will likely drive the circuit bonkers, what you really need is an LC-tank circuit (a resonance circuit), followed by a rectifier and some amount of amplification - like what is used to adjust transmitter antennas for peak performance.

How much gain is needed is impossible for me to say, as I don't know how much your transmitter puts out, but you're welcome to send me a PM if I can be of any help.

Thanks, I'll give it a go. It looks easy enough to make an LC tank circuit. If I get into trouble I'll PM you.

Sure thing, good luck and have fun :)

Hi mate this looks a great tutorial as I am just starting out, I would like to have a go at this but don't have any BC547, all I have is a bag full of 2N3904 - are these no good? Thanks John :)

2 replies

The 2N3904 is very like t he BC547 and will work as a replacement.

Hello, thanks very much for your quick reply.... John..:)

I take it the yellow wire in the circuit diagram is the antenna? Any idea how much added sensetivity you would get with a coil of wire (take advantage of the induction properties of a coil)?

1 reply

Hi Mike,

Yes, the yellow wire is the "antenna".

The inductive properties of a coil will do jack - unless you make it huge enough to be in resonance at 50Hz or 60Hz (whatever your mains frequency is), or something close by, with the input capacity of the first (leftmost) transistor. This capacity is very small in this respect (around 9..10pF depending on manufacturer).

To get resonance at 60Hz, you need a coil with an inductance of 700'000H to 800'000H (1'000'000H to 1'120'000H for 50Hz) - around 1MH (mega-Henry).

Usual coils for radio work goes down to nH (even pH) and the largest coils in normal DIY settings are around 100mH or so. If you connect around 10 billions of those, you're about there, or IOW, not gonna happen!

Another problem with asking for added sensitivity is that, electronics is a game that needs quantitative measures rather than superlatives. First you assert the sensitivity of the circuit, then you figure out how much better it needs to be for your application (in numbers) and only then a solution can be found.

This particular circuit is not as sensitive as it could be - funny, as it apparently comes from the hand of a guy, who dedicated a huge page on his site to bash other peoples design flaws. Doing so, one needs to be careful of own design flaws.

I've added a more sensitive schematic. R1, R2, D1 and D2 is for protecting the circuit (and could be added to the original circuit as well). It takes care of high voltages on the input. R3 can be made 1M if you like. The purpose of C1 is to lessen the apparent flickering of the LED (which will flicker at the mains frequency). The flicker could be removed completely, but at the cost of a slow reaction time.

If you have a specific sensitivity need, please post some numbers and the intended application and I'll be able to tell you, if either of these circuits will do, or if a completely different method is needed.