Lodestone PICO

The PICO turns audio into magnetic fields you can feel. It has the very portable form factor of a USB-C stick. It is plug n' play on mobile and PC. It's not very powerful but makes up for it by being completely passive (no need to charge) and very practical for everyday use! Simple is better!

⚠️ Warnings & Instructions

• The PICO registers as "headphones" when plugged in. Some Android devices are known to have a hard time detecting headphones on their USB port. This is not specific to the PICO. There is no known solution to this other than plugging it in a couple of times until it works. Hopefully, a future Android update will fix that.

• The PICO is not actively amplified. It is strongly recommended to use it at full volume.

🚀Specifications

Device

• Dimensions: 28 * 13 * 8 mm

• Outputs: mono audio (could be DIY'd with stereo)

• Average output strength: 0.424 mT

• Amplified: No

Compatibility

• Any device supporting USB-C audio output.

Performance

Frequency response

The PICO has been and is still being analyzed with a professional Gaussmeter. All the data collected is made public in this repo:

• Frequency response

With ZINC (over the useful 0-500Hz range and with sine, square, and saw signals) the PICO has an average output of 0.424 mT and a max of 0.517 mT.

🧰Do it yourself

Difficulty: ⭐

Price: 💸

Parts

• AL5686 USB-C dac-amplifier module | Source Example | Other Source
• 0510 axial inductor: 1 mH | 5.9 measured Ohms | Source example
• Small diameter heat shrink or equivalent

Tools

• Soldering iron
• 3D printer

Assembly

The inductor connects to the right channel and ground. The left and mic are left empty. If you would like to use the 3D files provided to enclose the PICO, then please make sure to align the inductor well with the end of the board by pre-bending and cutting the legs very short. The inductor should sit flat against the end of the board as seen in the images.

• Start by pre-bending and cutting the inductor leads. Bend them as tight as possible, right against the inductor body.

• Use a short piece of heat shrink to cover the longer lead as it will overlap with the mic and left pads on the board. Alternatively, you could also cover the pads on the board with some substance.

• Solder the inductor to the board making sure to keep the alignment perfect and the inductor right against the edge of the PCB. This part can be tricky so find a way to hold both pieces in place while you solder. Pressing them on double-sided tape can do the trick.

• Print all three files here. They can be printed in PLA with no supports (domes upwards) or in resin.

• The board is inserted into the "body" piece with the USB sticking out of the USB-c-shaped hole. The smallest "tip" piece is glued on the back to enclose it. The medium "cap" piece slides onto the USB-C and might need some filing for a perfect pressure fit.

You're done 🎉 Now plug it in and try it!

🩺FAQ

• Does it work with iPhones? The USB stick, yes (if your IPhone has a USB-c port). The ZINC app won’t be on the Apple store any time soon but you can still use it with other apps that produce sound.

• How strong is it? It is decently 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 a 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? Nope.

• 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.