How to create electromagnetic interference?

Hey guys.
I'm designing a project which consists of Arduino + long wires connected to buttons so I needed to test it and see how resistant it is to EMI. (Because the long wires can act as antennas).

I looked for material about this online but the only thing I could find was this link.
I tried what is suggested there but it did not work.
However in the process, by pure accident, I was able to create electromagnetic interference!
I have this old linear adjustable regulator and I realized when I plug it in and out, my PC speakers give out a very strong sudden noise. I figured this has to be EMI from the supply. So I hooked up my Arduino and my long wire to an input and voila! The input pin (even tho it had a 10k pullup resistor) would get triggered multiple times when I plugged the supply in and out of the AC outlet.

This was great news and I was able to test different filters.
Now I'm wondering what exactly is creating this EMI? (I'm assuming it's the transformer)
And how can I create a device that does this? Plugging in and out the power supply isn't very convenient and I'm not sure if it gets damaged in the process. So I wanna make a standalone device for this kind of testing in the future.
Also is it possible to change the strength and perhaps the frequency range of the EMI created?

The radio frequencies that are used to transmit start at 3kHz (Very Low Frequency band) up to 39GHz (for 5G). That is a very large range. Those frequencies can travel through air.
When two wires are along side each other, then they are inductively and capacitively coupled, and the 50Hz/60Hz from the mains in one wire can cause trouble in an other wire.
That means about anything is possible.

High voltage peaks and high current peaks can be the cause, but the best source of EMI are sparks. Sparks create pulses on many frequencies. Plugging the old power supply in and out might cause sparks.

Did you know that sparks were used in the first radio transmitters ? I think the Titanic had one of those.

Thanks Koepel.
I don't think radio frequencies can create much interference.
I'm mainly interested in the 60Hz from the mains power as you mentioned, and any other source of EMI that can happen in a house or in an industrial place like when someone turns on a motor, etc.
I want a device that is able to create EMI similar to those so that I can test my designs.

I'm sorry, but I can not answer your question. It is probably not legal.

There is of course test equipment. But then you also have to know how to use them.
When equipment is tested, they do that in a room/laboraty with a specific setup. However, in a normal situation, even in a normal house, things can be very different and the EMI is unpredictable.
I think that the best option is to avoid it by using a shielded cable and perhaps optocouplers to isolate the Arduino from the long wires.


So that's why I can't find anything online about it?
I don't want anything crazy tho, just something that creates interference on the level that is created in everyday situations. Like turning on a motor as I mentioned stuff like that.
I think I can create a good amount of EMI by making a high voltage spark gap but I was hoping for something simpler.

It's done!
This is the best EMI generator, cheap, wide spectrum, authorized! this is not a joke. Rub a soft ferric metal (in the shape of a plate, it's better) on the file, or on the brush, near the electric extension cables which arrive on the circuit, or near the processor. Seriously!


Will any file do? Or are these special files?
And how does this exactly work?

Old rusty files are very good! or new hardened steel ones. In fact, all are good. Rubbing them with soft iron generates multiple sparks (even if you can't see them) which cause fast rising parasites on electrical connections, with lots of harmonics. This is used in labs in addition to extremely expensive generators.


  1. How long are the wires to the Arduinio?
  2. What model Arduino are you using?
  3. Why are the wires long, why can't you place the controller at the buttons?
  4. What is the application?
  5. Have you tried twisted pair?
  6. Have you tried shielded cable, single or multi cored?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

That's interesting I didn't know that.
I'll see if I can find iron and test this.

Thanks for the reply Tom.
My specific purpose in this thread is to make something that can generate EMI so I can test stuff with it.
The project which I mentioned was just the back story. I already tested it with the EMI generated by the power supply, and some basic RC filter on the inputs + software debouncing completely eliminates the EMI-induced false triggers.

Absolutely useless, no electricity is involved at all, this is purely a chemical reaction (fireworks don't interfere with radio, that takes lightning!)

If you want electrical sparks, a universal motor (common in many household appliances) is quite a strong source - a power drill for instance. Old fluorescent striplights tended to put kV pulses on the mains wiring of the building when switched on and off!

Ah ?

pourduino, another very good EMI generator.
Do this: with a file and rubbed metal, or the electric igniter, test all the electrical equipment in the house, making sparks near the electrical connections. The ones that crash (there will be some) are poorly protected

Ah yes, Wimshurst generator - that will work nicely! (Be careful with them, if the Leydon jars are connected they can deliver a dangerous shock level - defibrilating a normal heart rhythm is not benign!)

Another obvious source of interference is a vehicle engine compartment if its a petrol engine.

I forgot. DO NOT TOUCH THE ELECTRICAL PARTS WITH THE ELECTRICAL LIGHTER! This is only a REMOTE test. Do not do this test on new and expensive household appliances, only on electronic tinkerings.

Actually it is exactly the radio frequencies that transmit the interference.

Both capacitive and inductive propagation effects are directly proportional to frequency.

The most readily available generator for intense broad frequency interference is a "stick" arc welder. :sunglasses: But you have to actually strike the arc.

Now that is illegal all over the world.

Spark transmitters are illegal, but sparks in themselves are not (otherwise the petrol car engine would be illegal!) Lightning isn't illegal either. (Few human-made sparks are as bad for interference as a thunderstorm!)

The easiest method for the OP is use a 18 inch single lamp fluorescent light to wave around the project. The lamp needs to be one with a magnetic ballast. The lamp produces and quenches an electric arc in mercury vapor twice the frequency of the mains power. Between the arc and the magnetic flux from the ballast, they will get a full range of electro-magnetic interference! And they will have a light to see what they are doing.
Of course, the Arduino will likely stop working because of the interference.

My mother's sewing machine is a great source I think. When she operates it I pick up strong noises in my speakers on my PC sitting 2 meters away from the machine and separated by a wall. This is the exact noise that the power supply I mentioned makes.
But like I said I was hoping for something small and easy to use.

I actually tried with one of those igniters and it did nothing. I made the cable (5m) into a loop and did the sparks right over it but nothing.
The power supply tho, the moment I plug it in it wreaks havoc on the Arduino input.

That sounds too dangerous and complicated I don't want something like that.
Is there really nothing I can do to replicate whatever is happening in the power supply? Preferably with DC cause I'm not comfortable with AC.

There are tutorials on youtube. :sunglasses:

Can you elaborate what do you mean by between the arc and the ballast?