TL;DR: I made a circuit-board business card with an NFC chip and a batteryless LED powered by the phone tapping it. The hardware worked, but ordinary iPhone NFC apps couldn’t format the blank NTAG I²C Plus chip. I wrote a tiny Core NFC app that sends the chip’s native commands directly, and now each tap opens my site and lights Charizard’s tail.

I wanted a business card that wasn’t a piece of paper. Not out of some deep philosophy—I just thought it would be fun to hand someone a circuit board. So I designed one: credit-card sized, glossy black, with gold artwork and my name on it. Standard so far. The two things that make it not-just-a-card are both invisible until you bring a phone near it.

The first is an NFC chip. Tap the card to a phone and it opens kevintang.xyz —the same technology as a tap-to-pay card or a transit pass, running at 13.56 MHz [1] .…