Overview
- Two independent hands‑on reports confirm working, business‑card‑sized PCBs that use a printed trace antenna and rectifier to convert a smartphone’s NFC field into milliwatts of DC power to boot an onboard MCU and light LEDs.
- Designs and files for functioning prototypes are available on GitHub and include examples such as a 21 Charlieplexed‑LED card, proving the builds are reproducible and manufacturable.
- Real‑world performance varies because phone NFC transmit strength and antenna tuning determine available power, with testers reporting generally consistent results on recent iPhones and reduced field strength on some Android models.
- Higher‑end approaches use dedicated energy‑harvesting NFC chips (for example STMicroelectronics ST25DV with a V_EH pin) to provide steadier milliwatt‑level power, while makers often use tiny MCUs like the WCH CH552 or ATTiny series to stay within the tight power budget.
- The maker toolchain is accessible—KiCad layouts, STM antenna tools, and low‑cost PCBA houses such as JLCPCB let hobbyists and small vendors prototype cheaply and pursue profitable small runs given reported unit costs well below typical retail prices.