The Casio F-91W digital watch is perhaps one of the most successful pieces of consumer electronics ever made, having quietly supplied the essential function of an inexpensive and accurate LCD digital timepiece for many decades. As a result it has a huge following, and we’ve seen plenty of projects based upon it. [Matteo P] has one that we think you’ll like, he’s turned his Casio into a contactless payment device. We missed it when it came out, but sometimes a good project needs sharing.
If you’re a long-time Hackaday reader you may remember our investigation of 13.56 MHz NFC cards in which we showed you a disassembled card in which he antenna was a tuned circuit covering most of the card, with a small coupling coil for the chip. It’s this kind of card he uses, and ends up with an SLA printed front face for the watch that places the chip above the display and puts a pick-up coil around the outside. The most interesting part of the write-up though isn’t in the build, instead it’s the deep-dive into designing the RF parts and ensuring a good coupling at something close to resonance. Read it, if you fancy trying NFC-enabling any other random items.
Meanwhile, if this NFC bug has caught you, don’t forget our rather silly one transistor 125kHz NFC reader challenge.
Thanks to Hackaday alum [John Elliot V] for the tip!
probably can remove most of the IC contact pad as well. the actual IC die is likely much smaller.
Very limited security. No.
Apple Watch has multiple security controls for their watch and payment system, while this one has virtually none.
Apple Watch requires an unlock code be entered when the watch is placed in the wrist, and is re-locked if it is removed. (Phone can be used to unlock it as well, in a fairly friction free process.)
Apple Watch also requires a button press (twice actually) to activate. This combination makes it reasonably secure.
This device instead may have a single push button, that’s it.
At least it has security by obscurity (for now): nobody on earth is going to know that dorky old watch with some random crap stuck to the face is actually your money
The moment you see him pay publically that obscurity goes out the window. And as somebody with an Apple Watch I can absolutely say people notice when I pay with it.
You know many people (hundreds of million if not billions) use credit-card size bank cards for payment, and they have sound security.
So if you take a bank card, dissolve it with acetone or something then use the chip and make an alternative antenna coil then you can stuff it into a watch and be completely secure.
Now thinking freaking smartphones are so 1000% secure and unhackable.. well that’s a view surely..
It seems best to use this with a card that doesn’t contain your entire life savings, rather something you can easily reload with a few pesos at a time (cash app card).
Jenny, I hate to break it to you, but I think that’s FDM printed. At first I thought it was just some tape stuck over the top, but when you said it was 3D printed I realized you were right, but I think I see the nozzle pattern on there. SLA would probably work better.
What, no links to any of the other F-91W projects on here? I’ll get you started:
https://hackaday.com/2021/01/22/casio-f-91w-going-dark/
https://hackaday.com/2021/08/08/wristwatch-pcb-swaps-must-be-in-the-air/
https://hackaday.com/2019/06/04/waterproofing-the-best-watch-ever-made/
https://hackaday.com/2016/05/30/gutting-and-rebuilding-a-classic-watch/
and here’s another NFC one, this time to unlock a car: https://hackaday.com/2020/09/04/see-this-casio-watch-it-unlock-my-tesla/