This should be the final revision. Just a few minor tweaks. The regulator is now a TPS77533 rather than an incorrectly footprinted TPS77333. Corrected the bi-colour LED wiring. Move to a smaller 4MHz crystal for the USB side of things. Shrunk it a bit as I’m no longer expecting to find any PCB bugs. Dropped the 0.1″ pin header as the TagConnect worked fine.
The most obvious change is the small capacitive touch sensor PCB on the front. The previous version searches for a tag a couple of times a second. This works fine but I don’t like the idea of all the 13.56MHz EM noise pollution. This will poll for touch frequently and if it senses a touch it will poll for tags rapidly for a few seconds. In theory it could be more responsive too. Not had a chance to code this yet though.
There’s is also a Login NFC the way to another implantee. I’d recommend you check out Hans Peter’s embryonic.dk blog.
0xFRED 
Dear Fred,
I just recently got an xNT implant and am working on designing a reader/writer board. Being a student at University College London, your blog brought great interest on my behalf and on behalf of many of my fellow colleagues.
I was hoping we could exchange some emails and share ideas on custom antenna designs and small form factor integration for implantable tags. As it unfortunately seems ,research on a university level is still in its very first years with regard to reading human implantable tags with any practical range.
Please do let me know if this is something you could help me with,
Kind regards,
Vasco
I’ve been thinking about trying an optimised PCB antenna myself. The coil is good but I wonder if it could be better. Happy to collaborate on this. I’ll drop you an email.
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