We went over this one in leeborg’s thread (no worries, there’s alot of information here). You wouldn’t be able to frame the xLED in the middle of that coil with the middle cut out because the xLED would need to be poking straight up out of your body. If you wanted to use that coil you would need to lay it directly over top of the xLED, which blocks it. That’s why we’re planning a bracelet coil, because the field lines are running parallel with your arm, just like the xLED would be under your skin.
Just to clarify, the PCBs are made of fiberglass, not silicon, and it has little to no affect on magnetic fields.
I’m really curious to see where this thread goes, I’d love to get an xLED but the only thing holding me back is nothing to keep it on twenty-four-seven. But it seems like you guys are solving that!
At this point we have a working POC. Obviously it still needs lots of work but I feel like we need to work out some constraints so we can start looking into how to optimise the solution for those constraints.
For example I was pumping ~6W into the circuit (30v @ 200ma). Is this too high? How are we going to power the system?
What is the minimum useful range?
Is it okay for the coil to “frame” the implant?
Do we need to mount everything to the bracelet or will we have to externalise some things? For instance a battery in a pocket with a wire running up the arm?
Input from anyone who would be interested in using one of these would be valuable just to get an idea of use cases etc
For my case, I think I would put the battery packs into one of those arm sweatbands, so I could wear it as close to my shoulder as possible, with the wire coming down the inside of my arm. I don’t plan on wearing it daily, so I can tack down the wire with a bit of tegaderm along my arm.
It would be great if we could minimize it to the point that we could use a few coin cell batteries and keep it all on the band. The band could even be a transparent plastic so you really can’t see anything but the coil and circuit in a tiny case. I think the only way to do that would be switching to 125kHz and making a small ferrite core coil with tons more turns. We’d have to use LF xLEDs, though
I do have some parts coming for a 125KHz circuit. Also I think it would be easy to get a microcontroller to output 125Khz so you could have like a Morse code blinking implant.
Oh damn, I didn’t even think of that. You’re probably right. Eventually the driver circuit could be on a small PCB with a microcontroller, and we could leave 4 test points exposed to reprogram the thing. Could even put a little DIP switch on there to flip between a few different configs, and a little smt pot to adjust the blink intervals.
@TomHarkness is actually the guy working on this, but the project has been derailed several times. I can tell you that the NTAG216 has a 50pF capacitance which means the inductance of the antenna for the NTAG216 chip anyway is around ~2.75uH … and in general, it’s better if your antenna inductances are at least close to each other.
Also smaller wire diameter is a good way to get voltage up, at the cost of current transmission… but current isn’t really a big need here since you’re dealing with LEDs and such… getting a strong / large field by way of higher voltage is more important.
That’s a good idea, I will get some thinner wire, I have been using the thicker stuff because it hods it’s form much better but I can just 3d print something to wrap the wire around.
Yeah, so far i have been like 3 to 30 times that inductance depending on the coil I tried, I will try match it.
The signal from the pierce oscillator is also quite messy, I don’t know how much that would effect things. It’s distinctly a sine wave but its not clean at all (could be my shitty o-scope though).
