Lodestone PICO : Finger magnet fun for everyone

The Lodestone PICO is a simple USB-c stick that takes your phone’s audio and turns it into a magnetic field you can feel with your fingertip magnets. Its design is open-scource and you can find all the information and files about it here:

Original Post

This is a simple USB-c stick that takes your phone’s audio and turns it into a magnetic field you can feel with your fingertip magnets.

Old pics

It can be used with the app I’m designing to play around with frequencies and modulation and discover the full range of what you can feel.

You can use it of course with other apps too (like music) since it registers as an audio peripheral (like headphones).

Make it yourself

If you have some electronics experience this couldn’t be any simpler.
It consists of an AL5686 USB-C DAC module and a 7mm axial inductor of around 12Ohms and 1mH.
The inductor connects to the right channel and the left is left empty. If you decide to use one for each channel make sure they are aligned and in the same direction otherwise, they tend to cancel out.
The casing is 3D printed. I can provide the files.

Performance and disclaimers

Does it work with iphones?
The USB stick, yes. The app won’t be on the Apple store any time soon. Android for now.

How strong is it?
It is surprisingly strong at a 1-5mm range within the frequency range that you can feel. You lose any feeling
at over 1cm. That said you need to keep your phone’s volume at max or close to max. I can’t really explain much more than that since there’s no good point of reference.

Does it make sound?
Nope. If you stick your finger in your ear and get it close you can use your finger as a headphone though. Fun party trick.

Does it heat up?

Could we make it better?
I got slightly better results with custom coils (like 10-20%) but the sheer simplicity of using off-the-shelf modules makes it cheaper and much much easier to make.

Should I make it myself?
If you have the tools then sure, you can find the parts online.

What to expect from the app?

The app already has a fully-fledged signal generator to play around with. It is free of ads as opposed to most other signal-gen apps and is specifically designed for this purpose with other implant-related tools.

IF a decent number of you are interested and willing to test my stupid ideas then I have further plans involving this concept. That includes some minigames, a standardized sensitivity test, and maybe some augmented reality stuff. This all ties in with my previous research in the field. But this is stuff I do as a hobby now so I’m not giving any details, timelines, or such, yet.

With all that said I live in a remote place where I can’t order the materials online very easily. BUT in a couple of weeks, I’m flying to France and will be able to stock up and produce some for whoever wants one.
I can make them at the cost of the materials (~12$) + shipping to your location and let you decide on a tip. Please answer asap so I can plan accordingly :wink:

[poll type=regular results=always chartType=bar]
  • I will buy one from you
  • I will make it myself
  • I might buy one but am willing to wait a long time
  • I have a magnet but I’m not interested
  • I’m not sure what it does
[/ [poll ]

Please excuse the crappy 3D-printed shell on the photo and the quick soldering job. This is a prototype with crappy filament. I’ll make sure to make yours much cleaner.


Just spitballing, but could you reverse it into an input? Like a theremin?

Don’t let the question derail you. Incredibly cool device. :+1: I bet it makes Postsmaster wish he was a real boy so he could play with it too.


Funny thing, almost all mobile phones have an integrated hall-sensor but we usually call it the compass because that’s what it’s used for. But it is in fact what you are describing and I’m using it in the app as such :wink:

Edit: Although these chips I’m using do have a microphone input that could be theoretically set up in a way that it senses your magnet. That would be cool!


en métropole ! :joy:

So :nerd_face: is it possible now to compare magnets’ sensing capabilities on a rather empirical way?

:pancakes: that I don’t have sensory magnets implanted atm :cry:

That’s the question I was hoping for! :grin: you get a gold star :star:

It will be possible to compare the following:

  • Amplitude detection (the faintest detectable signal per frequency)
  • Amplitude discrimination ( the smallest detectable change in signal strength per frequency)
  • Frequency discrimination ( the smallest detectable change in frequency for a given amplitude)
  • Temporal discrimination ( fastest detectable changes in signal)

These comparisons will be done with the following assumptions:

  • All mobiles output audio through their USB C the same way (probably mostly true)
  • The emitting devices perform identically (that’s why I made this post)
  • Users proceed to the same tests (the app will take care of that)
  • Users use the device optimally (I mean just get your finger very close to it)

Notice I said “compare” not “measure” as the results will not really have units related to the signal strength.

Ie. I can feel 100Hz at volume 60% with the device.

To be able to put this into quantified units I or someone else will have to characterize the device with a Tesla meter, adjust for the inherent differences in power over the frequency range etc…

Then you would get something like :
I can feel 100Hz at 0.1mT

I might have skipped some things but you get the idea


If you need any help with that lmk. I’m in the US


That would be sweet… I will try and get everything during my trip this time but if I run out in the future it would be super helpful if you can relay a couple packages :pray:

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I should have also thought to offer; So If you ever need something from as far away as possible in the antipodes, Let me know

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Haha thanks but I’m colser than you think. I’m on a little piece of France in the Caribbean :desert_island: hence why I can’t get anything delivered. It’s basically double the price of the item to get it shipped plus import fees and that’s assuming the vendor is even aware of these islands. Basically we have a couple big families here who have the monopoly on everything and will freely manipulate the taxes and fees so that you can’t buy anything from the outside. This way they can inflate their prices as much as thay like.
Most grocery items here are 3x or 4x the price in continental France :face_exhaling:

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It took a few iterations but I got a satisfactory 3D-printed case for the USB-C stick. It minimizes the thickness of plastic between the inductor and your finger and at the same time the overall size (it’s so cute!).

Again I’m using my crappiest filament for test so bear with me
Here are the files:
DAC2Round.stl (193.6 KB)
DAC1Round.stl (41.7 KB)

These are for 0410-sized inductors.
That said I will include some slightly larger inductors (0510) in my order so if they turn out better I will be doing some more adjustments and swapping for those.

Edit: I’m adding this here
ALC5686.pdf (1.7 MB)
in case someone with more experience in ics and pcb design wants to take a look. I see a bunch of pins in there that could be used in interesting ways like:

Edit 2: Here is a cap for 3D printing:
Mini USB DAC Cap.stl (104.1 KB)


I will be ordering the chips next weekend so I bump the thread in case some people missed it :arrow_double_up:
So far I’m counting 10 here and a couple on Facebook.

For those who replied I don’t know what it does:
It plugs into your phone and you can tickle your Titan or any other finger magnet on demand with (almost) any frequency. This will allow for standardized testing, games and more. If you have questions throw them at me :wink:


Will there be a new standardized measurement of magnet feeling called Az Units? :stuck_out_tongue:


Nah, as long as the device itself hasn’t been properly measured we would use relative measurements which wouldn’t necessarily have a unit
See Finger magnet fun for everyone - #7 by Azflyer

But I wouldn’t mind Az units :grin:
I can already see the titan’s product page on DT: “The highest Az-rated finger magnet around” :joy:


For those printing it I added the file for the cap in my earlier post.
The tolerances are pretty low. Depending on your print quality you need to file a bit of the hole until you get a nice pressure fit. Otherwise it would fall of.


I suggest the Az-Kaban ! :stuck_out_tongue:


Order placed. I’m flying to France in a couple of days to grab all that and will be back home in june. At that point, I can start making them and sending them out.

If you voted “I will buy one” please start sending me your shipping address + name and number.
I expect about 12-13 people from this thread and 4-5 more from other platforms. I can’t see the name of the voters so I trust you to contact me :wink:
I will be making some extra but not that many so if you want a couple let me know asap.

Also, these little USBs need a name, what do you think:

  • The PicoTesla v1
  • The Lodestone Nano v1
  • The Haptic Pebble v1

0 voters


Force Mineur


By the way your Loadstone PICOs (final name) will be either black or white with a gold plated USB… let’s say it’s an early bird special edition :joy:


for next time

I would have called them Bob