March 1, 2020 · project hardware

Modding payWave into my Casio F-91W

The Casio F-91W almost has a cult following due to its cheap, reliable, low-key design, and legendary 7+ year battery life. Mods range from replacing the standard resin straps, changing LED illuminator color, to full on replacements of the internals to include a SD card! Obama has been photographed wearing it, but it has also infamously nicknamed as the "terrorist's watch" after its use in time bombs made by terrorist organizations.

Coming from an Apple Watch, I missed being able to make contactless payments. But after an evening's tinkering, I managed to put my payWave card into my watch 🙂.

Me buying some KFC with my Casio.

My bank offers these Gemalto stickers which is a shrunk down version of a normal credit card without the magstripe or the chip, only contactless coil. It was originally launched before Apple Pay and Google Pay arrived in New Zealand as an poor man's mobile payment alternative.

After submerging one of these tags in acetone for an hour, the plastic card dissolved off leaving the NFC induction coil and chip exposed. With a bit of care and cleaning, I rewound the coil to fit in the body of the watch, glued it in place, and repackaged the watch together.

Now I have a fully functioning retro Casio watch , with a secret ability!