HF LED Power Accessories

Community Project: HF LED Power Accessories
Anyone who would like to contribute feel free to add your thoughts here. If you need to make purchases to support your contribution to the project, see this thread, and direct message @amal or @Satur9 with details. Project threads can get a little out of hand with tons of people brainstorming. I ask that you limit your messages to the topic at hand. Try to condense multiple messages into one post

A team of forum members and I have been attempting to design a wearable device that outputs a HF signal to power LED implants. It is purely for aesthetic purposes. The first build will be a bracelet, but it could be adapted to other form factors after some testing.

The project has died down over the winter months, but I invoke the power of resurrection now and summon the team members!
@Vicarious! - @Leeborg! - @Naus3a!

Unfortunately I can’t find @Haruspex on here, but I suspect my Shout will echo to the halls of Discord.

The new member @leumas95 has summoned us to action. If we loop in everyone else on the forum, we may actually get a working prototype out of this and we can format it as an instructable or something.

There’s a bunch of legacy info we can loop in if need by, but here’s an update on where we were at last check. I figured out how to make a Pierce Oscillator

Rough Schematic

Breadboarded Circuit

Oscilloscope Output

Hypothetically an appropriate inductor could be placed in series with the 1kΩ resistor at the beginning. I tried a couple through-hole discrete inductors I had lying around, but I wasn’t able to light the HF xFD. There’s also the possibility of connecting the gate of a high switching speed mosfet to the wire labeled “OUT” in the diagram, and using that to control current flow to the coil.

There are also other types of oscillators I haven’t gotten an opportunity to fully test out yet because they rely on inductor and capacitor tuning, not a tight tolerance crystal oscillator.

There is a ton more that can be done in this area I just don’t have the bandwidth to address it at the moment with other priority VivoKey development and my full time job. Feel free to contribute in any way you can.

Stretch Goal:
Resonant circuits that light LEDs from up to a meter!


this is really cool!! if it enters into any sort of mass-ish production, i’d definitely be interested in buying one.

unfortunately i can’t provide any technical help, but will be cheering you on from the sidelines!

just out of curiosity-- would this be designed to ONLY work with HF xLEDs, or would it also work with xSIIDs? i assume it would, but would it react differently because of the data transfer capabilities of the chip?


It would just be a passive power source, so it would work with the xLEDs, xSIID, xFD, and diagnostic card. No communication, just a 13.56MHz magnetic field blasting out.


Cool, loop me in hahaha

I mean the circuit should be fine what’s the issue or problem? Is it coil design or something else?

I’m willing to help out just tell me what you need :slight_smile:


The shout has indeed echoed to the halls of discord. I am very ready to revive the efforts especially now that many of us are slowly going insane out of boredom from home quarantine!


If you want an easy coil to play with, that’s well designed, why not modify an RFID diagnostic card?

It has both HF and LF coils. You’d just have to remove the LED and a couple surface mounted capacitors. Both would come right off with minimal love from a soldering iron.

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That’s so cool!!! I definitely going to do one of these as soon as my implants arrive at home.

The problem is kind of nebulous at the moment because we’re coming back to this months later. IIRC the problems were:

  1. Where to place the bracelet inductor coil in the circuit to generate a field (I’m thinking one lead can be hooked up to power, and the other lead can be hooked up to the Drain of a fast mosfet with a Gate connected to “OUT” and a Source connected to ground, but I haven’t tested it)
  2. Many RF circuits utilize a resonant tank circuit to tune the oscillations to the correct frequency. In this case would we need a capacitor in parallel with the bracelet inductor coil to create resonance, or can we just hook up any inductor and feed it a 13.56MHz waveform.
  3. What is the ideal Inductance/Resistance of the bracelet inductor coil to achieve the maximum range at 13.56MHz

This is awesome, I’m glad there is interest. This looks like it could be great fun.

I had not given it too much thought yet, I did see this thread and was looking for this kind of thing:

but based on my reading in that thread that would not work for the HF implants which I am not interested in as much (although I will probably end up getting some LF X Field Detectors just to mess around)

If you have any recommended reading for me it would be helpful, but your posts in this thread already gives me some pretty good jumping off points.

Totally understand (can’t wait for the new VivoKey stuff)
It will probably a bit of a slow ramp up for me anyway, I moved to the USA semi recently and I need to reacquire most of my electronics stuff before I can start tinkering, so I am mainly reading up on stuff atm.

That would be fucking epic! Would we need to tweak the implants themselves to get range like that? It looks like it might from skimming that page (I am meant to be working so I am resisting getting sucked down a researching rabbit hole)

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This was a good resource I found before this got back burner do

Check out the spread (unfolds centerfold)


thanks for reviving this :slight_smile:
In these pandemic times I’m locked away from my hardware toys, but I’m really happy to see renewed interest in this!


Possibly. What we need now is for someone to dive into researching that. It’s easy enough to test it out, and if we can prove it and people are interested we can look into making special resonant xLEDs.

Also found the answer to questions 1 & 2 from above:

From that “Build Your Own Inductive Charger” schematic above, I see that you can in fact hook a mosfet up to the output of the oscillator. Then you need an appropriately sized inductor and capacitor to create resonance.

Tasks people can jump on:

  1. Bracelet size:
    The size of the inductor will have to be determined by the size of the band we want to create. Can someone figure out an appropriate size that could fit most people? We may also be able to copy the design of those spring bracelets that expand to go on and then tighten without a break in the wire. If you could find pics or a guide on how to build those that would be amazeballs.

  2. Mosfet Sourcing:
    We need a mosfet with a safe switching speed above 13.56MHz that can accommodate ~100mA of current flow

  3. Research Resonant Inductive Charging
    If anyone is so inclined, could you do some research into this resonance thing and how we can get our hands on some actual hardware to test and measure. There may be chip manufacturers like TI that make driver chips and sell an evaluation board or something.

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That looks great, just the sort of primer I am after, thanks!

That it is a very good point, making a single bracelet size that would fit multiple users will be a challenge given we need unbroken loops of wire. It is also going to depend on where we want the bracelet. The wrist would be typical but hiding it higher under a sleeve also appealed to me, having it up around the upper arm may also solve getting it over the hand as the diameter of your hand is much closer to that of your upper arm (It would also make having an external battery in something like your pocket easier).

For resize ability It might be easier to look into options that allow for a break in the band. Ideas that come to mind would be using a flat PCB trace style antenna on a flexible materiel like this:
or a wire coil in a horseshoe kind of shape, but I am unsure how that would effect the field (I might try an get hold of FEKO or some other EM simulation software)

I will probably start by looking into a MOSFET just so I can try build a POC. On that note the xFDs are identical to the xLEDs other than the glass right? Would rather order them for testing than waste a xLED. I feel that having an xLED (or something analogous with it) lighting up would be a great first step and would probably help us with the sizing/form factor research.


Before I forget, we probably also need to look into if the implants would heat up with long term use. This may have been tested already.


Trying to wrap my head around this with my limited knowledge base, please forgive if this is off, or obvious.

Years ago…
I had a coworker who, through politics, ended up in control of our work radio. After 6 months of the worst programming, I kinda snapped.

This device is a battery pack, a crystal oscillator, and a short piece of wire used for an antenna. The actual oscillator chip is under the cover in the top corner. I wish I could show it, but it’s glued in place. That said, it’s about the size of your pinky nail, and has 4 solder points. 1 pos, 2 neg, 3 output signal, 4 not used.

I just wired it +, -, and output to the antenna wire.

It worked wonders forcing a truce on the radio.

While I realize, I was just pushing signal, and we need power, couldn’t it be nearly that simple? Use a fast Mosfet, and you could jump the power up. A battery, two tiny components, and an antenner wire. (suitably sized).

P.S. I’m thinking something arm mounted. 1 meter range not gonna happen this way, me thinks.

Something similar from Mouser

You’re on the right track. That’s almost exactly what I did with the Pierce oscillator. The only reason it needed more components was because I was amplifying the weak signal from the crystal.

There are two differences in your use case:

  1. The output is transmissive (in the far field). It becomes an electric field, it doesn’t remain a magnetic field like we need. That’s why it has an antenna, not a coil. Transmission travels much farther much more easily than induction.
  2. The receiving device (in this case a radio) has its own power source and amplifiers built in. A small signal from your device has a huge impact on a radio. The xLED only receives power from the field, there’s no battery or amplification. We need to pump out much more current.

Say I output one end to an appropriate coil. For arguments sake, I’ll say I violated an RFID Test card.
The other end of the coil would be ground.
I would probably definitely need the mosfet to “power up”

What else might I need.

I don’t need one of these, but if I get Covidededed out of work, then I’m probably gonna end up playing with it while I wait.


In addition to the mosfet to drive the actually coil/capacitor combo, you’ll also need all the other components in that schematic I posted. The crystal is putting out a signal, but it’s microamps at best. It’s nowhere near enough to drive a mosfet directly. You need to pre-amplify the output using a smaller transistor. That transistor also needs to be able to switch above 13.56MHz (like the 2n3904).

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Ah, now that makes sense.

Gonna keep throwing it at the walls of my mind till something sticks. I ordered a few components, cause frankly, I feel like playing with it. Thinking it’s gonna be fun. And I might even learn something.

Thanks Saturn9 !