How to Build a Pocket‑Sized NFC Smart Card with E‑Ink Display

A match‑box‑sized electronic card that combines a company badge, residential access card, and cafeteria card has gone viral after Bilibili creator "Zhi Hui Jun" released a DIY tutorial.

The video amassed over one million views in 30 hours and more than 100 k likes, and the source code has been open‑sourced for anyone to try.

Key features include storing multiple card credentials, rewritable data, NFC tag functionality, an e‑ink screen, and an app that lets users set the displayed content, all packed into a miniature form factor.

Hardware selection : the NFC physical‑layer chip ST25DV was chosen for its energy‑harvesting capability, powering the main controller STM32 L051 from the harvested energy. A CR2032 coin cell supplies enough power for the LED indicator and resolves NFC power issues.

PCB design was kept simple with a two‑layer board, though four fabrication iterations were needed to address occasional unresponsive behavior caused by NFC transmission power.

Enclosure features a rotary knob to switch stored cards and a physical button to refresh the screen and control the battery.

The e‑ink screen, limited to black and white, uses a dithering algorithm to simulate grayscale, allowing more natural-looking avatars and images.

Beyond simple card reading, the device can display to‑do lists, personal QR codes, and act as a portable secondary screen. Future versions aim to replace the monochrome screen with a color one, add on‑site card cloning, and support software‑based card emulation.

All design files, firmware, and documentation are available at https://github.com/peng-zhihui/L-ink_Card .