Listen to Protons for Less Than $100
Original: Build a DIY magnetometer with a couple of seasoning bottles
Key topics
Tinkering with a DIY magnetometer built from seasoning bottles has sparked a lively discussion about its capabilities and potential applications. Some commenters are exploring its uses, such as detecting submerged steel, with one pointing out a submergible sensor that can detect a known boat underwater. Others are comparing it to smartphone magnetometers, noting that the DIY device is far more sensitive, with a 0.1 nT resolution versus the µT range of phone apps like Phyphox. The conversation also veers into amplifier design, with suggestions for improving the output stage to drive headphones more effectively.
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Day 9
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- 01Story posted
Nov 29, 2025 at 7:04 AM EST
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Dec 7, 2025 at 3:28 PM EST
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17 comments in Day 9
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Dec 7, 2025 at 7:52 PM EST
about 1 month ago
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[1] https://alexmumm.de/pgProtonMagMarine_en.htm
[1] https://phyphox.org/download/
[2] https://alexmumm.de/pgProtonMagnetometer_en.htm
[1] https://en.wikipedia.org/wiki/MEMS_magnetic_field_sensor
[2] https://en.wikipedia.org/wiki/Proton_magnetometer
Using cheap bag-of-1000-for-a-fiver Chinese transistors off eBay I was able to get incredibly quiet output, to the point that I needed to add a muting gate because the radio was objectionably noisy. I notice that the exact transistors are not mentioned but any small-signal NPN and PNP ones will do - I used BC548 and BC558s, like I use in everything.
It will be way quieter and way more stable than an LM386.
Edit: I'm a lot better at drawing things in Kicad these days, and would have left the capacitors at the input a lot tidier.
https://onlyfandans.com/headphone.pdf
> the listening circuit must also be tuned to resonate at the expected frequency of proton precession, which will depend on Earth’s magnetic field at your location
> the frequency of these tones matches the magnetic field at my location to about 1 percent
I don’t doubt the physics, but I’m not sure about the experiment design. Being able to hear the correct frequency may just mean you’ve built an oscillator and tuned it.
https://m.youtube.com/watch?v=wg4GSXtpQzQ
This particular vid is a sort of FAQ