Capturing EM interference with a microphone

Jasen and OP:

You want to pick up the EMI and not pick up the acoustic sound. The best way to do that is to replace the microphone with a plain coil of wire. The coil will pick up the electronic/electromagnetic interference and not pick up the acoustical noise. You could also do that by immobilizing the moving part of the microphone so that it only picks up the EMI and does not respond to sound. That is just the opposite of what most people want, but having done EMI work for many years, the sounds of something working are very interesting. If you have an old LED display pocket calculator, try using that as a noise source, Listen to the difference between adding two numbers and getting the logarithm of a number, for example. You can hear EMI noise also from almost anything electronic.

One other possibility for just a very short time would be to stop the fan on your computer to stop the acoustic noise, SInce you have the computer out of the case already, you could probably run without a fan for a minute of two. Just don't stop the tiny fan on the processor chip if your computer has one of those.

H. R.(Bob) Hofmann

H. R. Hofmann

--
You\'ve got it backwards.  He _wants_ the EMI but _not_ the physical,
mechanical sound.

try to determine the frequency of emi and use a coil to resonate at that freqn. so that u pick up the max. emi and also with good power....

it also eleminates the need of very high quality amprs.....

also.......

the intresting thing with that sound is that u will actually pick up the data that is flowing through various cables and wirings of the PC.....

u can find more info regarding it on the web.......

bye.....

jh wrote in news:no-96791C.01580504112005@localhost:

with

even

to

movie.

repeated

spam.

Any way you can wrap the mic in a "sound proofing" material, so you damp out the acoustic pickup and leave the EMI sounds?

Try something like this...

|--------------- ----------------+---///////-------+--------| | | |-------------- K r | A | | | | | +-----------------+--------+

where the antenna on the left is maybe 6-12" of wire, K-A is a small schottky diode, 1N5711 maybe, R is 100k, output is audio coax.

Oh, ////// is a small inductor, 100 uH or something. This should pick up both baseband signals and detect RF. Drive a high-impedance audio input.

John

In fact the "crappier" the microphone the more EMI it will pick up!

No, that's the opposite of what he wants. He WANTS the EMI. A coil of fine wire, perhaps half an inch in diameter, with a hundred turns of wire or so should do it. You might be able to salvage such a coil out of an old speaker or headphone, Carefully remove the coil from the rest of the speaker structure, and connect the two wires to a microphone cable.

Jon

Forget the mic and use a coil !!

--
Regards ......... Rheilly Phoull

Thanks for everyone for your ideas. I'll try some stuff (when I get a chance; it might be a while) and post anything interesting. I'm hoping to eventually (maybe after I learn more about electronics) build a reasonably sensitive EMI-only "microphone" to use as a sort of computer stethoscope.

Here's my idea: could a computer technician, with this tool and some practice, hear and immediately recognize the EMI signature of a dying power supply or other bad component, the same way an expert pilot can instantly diagnose engine troubles just from their noises? Certainly, many technicians can recognize the distinctive sound made by some dying hard drives; but most components don't make any noise that we can hear naturally.

-- Josh

On Fri, 04 Nov 2005 01:58:05 -0500, jh wrote: ...

Sure! Just duct tape a piece of foam rubber over the part where the sound gets in. :-)

No, that's perfectly fine netiquitte, precisely because of spam, and not only that, but it's _bad_ netiquette to request private answers by email, (which you haven't done, so no worries :-) ) because the purpose of USENET posts is to share with everybody. :-)

Cheers! Rich

On Fri, 04 Nov 2005 06:14:35 -0800, hrhofmann wrote: ...

Oh, talk about reminiscence time! Back in the salad days of 8008s and

8080s and 6500s, BYTE magazine, or one of the wannabes, published a program that would play music through your transistor radio. It was based on the 8080 instruction cycle time, I think. At the time, I only had an 8008, so I wrote and hand-assembled a program to play tunes through a speaker - I was chicken to try to figure out how to do it by EMI. :-) I _was_ awfully proud of my interleaved loops, however. :-)

Cheers! Rich

On Fri, 04 Nov 2005 17:03:09 -0500, jh top-posted:

If it were me and my resources, in this day and age, I wouldn't bother. It's fun to probe around, and maybe play the sounds for your friends and stuff, but I seriously doubt if today's micro-stuff could actually be diagnosed by the sounds in the EMI. Well, you could hear an obviously dead component, but there have been trouble-shooting methods for that for decades.

For fun and education, yes definitely.

For a _real_ diagnostic tool, if you could pull it off, you could win a Nobel prize. ;-P

Have Fun! Rich

Hi Josh: The high frequency noise is from the cmos technology switching between 1 and

10 nanoseconds or 100MHz to 1 GHz. This noise passes thru the microphone cable and into the amplifier circuitry. At these high frequencies, the signal is rectified and what you hear is the peak detection of the noise. The only other noise is the switching power supply that creates a 1 MHz pulse every 20 to 40 useconds. Therefore, the best way to hear electronic noise with the existing amplifier is to just use a piece of wire about 2" long that connects the shied or ground wire to the signal wire. You don't even need the microphone. This is basically a UHF antenna. Enjoy Harold

the reason for that is that the dynamic microphone has a voice coil (like in a loudspeaker) anf that coil picks up all the electromagneic interferance (EMI) inside your computer.

You'll need to shield it against EMI. while not blocking too much sound that that won't be easy. basically you need to surround it with a conductive shell, electret mikes (like the "ctrappy lapel mike") are constructed that way.

Bye. Jasen

An easy way, use an in-ear earphone, or other earphone. They've got a coil of wire inside to pick up EMI, and a jack plug on the end. Tho they're comparitively lo-impedance but, it's an experiment innit?

Like others have said, put a bit of plasticine over the sound holes.

------------------------------------------------------------------------

if love is a drug, then, ideally, it's a healing, healthful drug... it's kind of like prozac is supposed to work (without the sexual side effects and long-term damage to the brain and psyche)

Using an earphone to capture EMI looks usefull to me, but I'm not sure I understood the principle. Please, what to do exactly with an earphone? Should I connect it to aditional power source (like batery) to drive the earphone, or no need? Should I, on the plug side of a cable, make something like antenna?

Nikola

On Tue, 8 Nov 2005 08:22:37 +0100, "Nikola Bosnjak" sprachen:

Just connect it to the mic socket on your tape recorder (or an amplifier or whatever), instead of a microphone.

It's a bit lo-impedance to be ideal, but should work.

No! Just plug an earphone into the mic socket. That's it!

Altho, as an experiment, you could try the antenna. Just a piece of wire, connected to one of the contacts on the jack plug.

I'd like to hear about your results.

------------------------------------------------------------------------

if love is a drug, then, ideally, it's a healing, healthful drug... it's kind of like prozac is supposed to work (without the sexual side effects and long-term damage to the brain and psyche)

Ok, you'll know when I get result.

Basicly, the point is to examine EMI in navigation devices on ships, becouse it can be the reason for some malfunctioning, sometimes. Using osciloscope or other measuring devices is hard (hard to cary it all the time when going to service). Once I saw a man wearing in-ear phones, probably driven with batery, and touching the electronic circuits with conductor (from earphones). He was using earphones instead of an osciloscope. So, what to do to use same principle to measure EMI?

Nikola from Croatia

I thought I posted something, but here goes again.

A telephone pickup coil is an inductive pickup. I think they still sell these.

I listen to noise via a portable handheld amplifier, just an op-amp. I have a switch to either connect a coil or just a rod antenna. The gain is adjustable. Noises from magnetic vs electrostatic can sound very different. Magnetic also penetrate metal. Static magnetic fields can be heard when positioning the coil, but a Hall Effect sensor would be best at this. I still need to configure to measure other noises. I need to connect a photodiode to listen to light noise, 60 Hz etc. DC light should be free of noise. I also need to measure vibration. A vibration sensor will connect to bottom of handheld device, so when its sitting on a table, the noise can be heard. I also need to measure LF audio, as in ventillation noise and changes of less than 10 HZ. This is not just a usefull device I carry, its necessary!

Therte is a product which is basically my electrostatic sensor It says inductive pickup, but I think its really just a rod.

greg