The Casio F-91W As A Contactless Payment Device.

A hobbyist named Matteo P embedded a contactless payment NFC chip into a Casio F-91W digital watch, 3D-printing a new front face that positions the chip above the display with a pick-up coil around its perimeter. The write-up focuses less on the build itself and more on the RF engineering challenge of tuning the antenna and coupling coil for resonance at 13.56 MHz, drawing on prior investigations into how NFC card antennas are constructed. The piece also points to a related one-transistor 125kHz NFC reader challenge for those interested in exploring similar RF hacks.

Source: https://hackaday.com/2026/08/24/the-casio-f-91w-as-a-contactless-payment-device. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.