Some of you are aware that I’m putting together a smart bracelet to turn my implant’s blinkies into a “smart” display of sorts. I have some bits and pieces - bits of code, test hardware and other things - and now it’s time to start putting everything together in what I hope will be something viable, not complicated to make and cheap. So I’ll be documenting this here.
Today I made a test inductor. A quick something to see if the implant lights up:
It works okay, but not well enough to power the LEDs through my wrist. More power is required I guess.
It doesn’t work. But that was just a quick test. I’m trying different antenna shapes - including some pretty weird ones - because one of the requirements is that the “bracelet” should look somewhat “artsy”, and clip onto my arm in an unintrusive and discreet way.
Right now I’m trying a sort of springy potato-chip-shaped figure-of-eight. It’s what I’d like the device to look like best, if field generation was no issue. It’s not doing it so far, and I’ve run out of the particular copper wire diameter I need, but it’s promising.
Nah… InGaN yellow LEDs have over 80% conversion rate, and I’m feeding something like 150 mW into the coil. Assuming half of that gets to the implant, not counting the power used by the bullseye itself, at most 15 mW is wasted as heat. For comparison, my body radiates roughly 85 mW at rest over the surface of the implant.
Actually I intend to embedded the final antenna in a custom piece of jewellery that I’ll make. The only trouble is, I know how to work metals, but this will have to be non-metallic obviously. So I’m not sure what material I’ll choose yet.
I’m thinking wood: It’s not great because it’s not totally non-conductive. But I like wood, and it can be springy too.
I figured maybe my body itself could act as an antenna. At high frequency, the skin effect should keep any current from flowing deep into the tissues. So I wrapped two bare copper wires around my arm, one in front of the implant, one behind, hooked myself to the function generator, measured the impedance of my skin at 10 MHz (it won’t go higher) and found more or less 300Ω. Then I cranked up the voltage.
I managed 35V peak. It hurts like a mofo, but no blinky action.
More like, I was in the lab at work - which is always dead quiet, since we assemble precision optical devices - trying to hide what I was doing from my coworkers for fear of being labeled terminally insane, and suddenly going “Oh ouch-ouch-ouch oh fuck that stings goddammit!”, instantly drawing attention to my upturned sleeve and the two leads connected to my arm.