Show HN: NFC Energy-Harvesting PCB Business Card with an MCU

A developer created an NFC-powered business card PCB with 21 LEDs that animate when tapped against a phone, harvesting energy from the NFC magnetic field without requiring a battery. The design uses an ATtiny microcontroller and Charlieplexing technique to control multiple LEDs with minimal GPIO pins, combining RF engineering with practical PCB design. The project demonstrates how NFC chips like the NXP NTAG I2C Plus can route excess harvested DC voltage to external components, creating a functional yet inexpensive alternative to battery-powered business cards.