Electromagnetic Sensor




An Electromagnetic field (EM or EMF) is a physical field produced by objects which are charged with electricity. It is one of the fundamental forces of nature and it is very strong and detectable in objects that use electricity. However, as much as we are surrounded by such objects we do not hear or see their EMF fields. The focus of this project is not the effects of EMF fields on the human body, but on ways by which we can detect and perceive EMF.

Our team used the EM sensor to make cymatic visualizations. To learn more, please visit our site at EM Cymatics.

Step 1: Getting Ahold of a Cassette Player

To execute this project, you'll need to purchase or ascertain a cassette player. The advantage of using a cassette player is that the EMF is converted into sound offering various creative possibilities. Though you would think the outdated technology would be easy to come across, it is actually rather difficult. Plan on spending anywhere from $15 to $50 on one purchased from Ebay or Walmart. Remember to always plan ahead and purchase a second one just in case. Cutting the wrong wire will stop the EM sensor inside from working.

Step 2: Locating the Sensor

After removing the initial housing from the cassette player, you should be able to spot the EM sensor near the top edge of the device. It looks like a little nub.

Step 3: Unscrewing the Sensor

The magnetic head of the player is very sensitive. To counter the sensitivity, the magnetic head is usually grounded to the chassis. Disconnecting the grounding screws makes the head more sensitive to EMFs. On either edge of the EM sensor, you'll see two small screws which are holding it in place. Carefully use an appropriately sized Jeweller's Screwdriver to free the sensor from the casing. Do not roughly pull or yank on the sensor as this may dislodge the wires from it. Good luck!

Step 4: Hearing EMF Waves

Now that you have disconnected the magnetic head from the chassis, you should be able to plug in a pair of headphones and hear an EM field. Give it a try by running your hacked cassette player across your computer's monitor, case, or keyboard. Do you hear anything? If so, move on to the next step to learn how to record the sounds you're picking up.

Step 5: Record EMF Sounds

In order to record the detected sounds, you'll need to purchase a 3.5mm audio splitter to plug into the headphone jack. Hook your headphones into one of the jacks and a personal recorder, such as the Olympus DM-620 SLV Voice Recorder, into the other. Make sure that your recorder has a 3.5mm input! When you begin to hear a new EM sound, press record to capture it!

If you've followed all of the steps, you're now ready to begin discovering and recording the EM fields in your life.

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    6 Discussions


    3 years ago

    Could this be used to find nails or metal in wood?

    An electromagnetic 'nailfinder' is expensive for the amount of use it will get but this would be real handy for 'pallet wood' builders

    3 replies

    Using it to find nails or screws in wood would be very difficult, the coil in the record/playback head is to small and not sensitive enough. You would be trying to alter a tone in an L/C field between the two. The head and nail would need to alter the field interaction of the magnetic field. The nail and head would barely interact if at all. A metal detector circuit would work much better.


    Reply 3 years ago

    An EMF sensor detects the electromagnetic field produced by the current flowing through an electronic device. There would be no current flowing through a nail embedded in wood, hence no electromagnetic field produced by the nail.

    What you could use for this is a pair of inductive coils, such as contained within a metal detector. Both coils consist of a matched number of wire loops and are kept in close proximity to each other. Current is passed through one coil, producing an electromagnetic field which, in turn, induces current in the second coil, and these currents are compared to each other. If there is metal nearby, part of the electromagnetic field is diverted away from the second coil, reducing the level of current induced in it. The closer the metal is to the coils, the greater the difference in current in the coils.


    Reply 3 years ago

    After conferring with the team, we believe that this use case is unlikely. However, if you would like to try, we would stress that the magnetic head of the cassette player should be as exposed as possible to increase its sensitivity. Try removing more aspects of the casing than were shown in this instructable. Doing so may just give you the degree of sensitivity you need.


    3 years ago

    I wonder if this is also a DIY pick up things in the area such as like what the spies use to find listening devices and such?


    Awesome idea! These would make a great electromagnetic sensor. And they are superI cheap.