The Casio F-91W is easily one of the most iconic and popular watches worldwide. But what’s cool about having the same exact thing as millions of other people? Not much, unless of course you modify it to make it your own. That’s exactly what [Gautchh] did to their beloved watch. Between permanent dark mode, stereo blue LED backlights, and a new strap, this timepiece really stands out from the crowd.
Once [Gautchh] got the watch open, the first order of business was to re-polarize the LCD with a different film so the digits are light and the background is dark. This watch ships with a single green backlight LED that’s fairly faint, so [Gautchh] upgraded it to bright blue and added a second 1206 LED in parallel on the other side of the readout. Finally, they replaced the rubber strap with something less likely to chafe.
We think dark mode looks great, though [Gautchh] says it requires a little bit of training to hold your wrist just right to make it readable. They make these mods look easy, but they likely aren’t for the faint of heart. If you want to give it a shot, there are good step-by-step instructions and several pictures to help out.
We’ve seen a lot of Casio F-91W projects over the years, including a method for waterproofing the internals. If you have a lot of love for this watch, why not make a giant version?
The whole point of gaining the remote unlock ability for our cars was to keep us from suffering the indignity of standing there in the rain, working a key into the lock while the groceries get soaked. [Mattia Dal Ben] reports that even Teslas get the blues and don’t unlock reliably all the time, in spite of the price tag.
[Mattia] decided that a spare key card might be good to have around, and that building it into his Casio F-91W watch would put the key as close at hand as it could be without getting an implant.
After programming a new J3A040-CL key card to match the car, getting the chip out was the easy part — just soak it in acetone until you can peel the layers apart. Then [Mattia] built a fresh antenna for it and wound it around the inside of a 3D printed back plate.
The hardest part seems to be the tuning the watch antenna to the resonant frequency expected by the car-side antenna. [Mattia] found that a lot of things mess with the resonant frequency — the watch PCB, casing, and even the tiny screws holding the thing together each threw it off a little bit.
Since the watch is less comfortable now, [Mattia] thought about making a new back from transparent resin, which sounds lovely to us. It looks as though the new plan is to move it to the front of the watch, with a resin window to show off the chip. That sounds pretty good, too. Check out the secret unlocking power after the break.
Casio watches are great, though we are more into the calculator models. Someone out there loves their F-91W so much that they made a giant wall clock version.
Continue reading “See This Casio? Watch It Unlock My Tesla!”
The Casio F-91W is probably the most popular wristwatch ever made. It’s been in production forever, it’s been worn by presidents, and according to US Army intelligence it is “the sign of al-Qaeda”. There’s a lot of history in this classic watch. That said, there is exactly one problem with this watch: it’s barely water resistant. [David] thought he had a solution to this problem, and it looks like he may have succeeded. This classic watch is now waterproof, down to 700 meters of depth. If you’re ever 700 meters underwater, you have bigger problems than a watch that isn’t waterproof.
The basic idea of this hack is to replace the air inside the watch with a liquid. This serves two purposes: first, the front glass won’t fog up. Second, liquids are generally incompressible, or at least only slightly compressible. By replacing the air in the watch with mineral oil, the watch is significantly more water resistant.
Filling a watch with mineral oil is done simply by disassembling the watch, submerging it in a dish of mineral oil, and carefully reassembling the watch. Does it work? Don’t know about this watch, but this was done to another classic Casio watch and tested to 1200 psi. That’s a kilometer underwater, and the watch still worked afterward. We’ll take that as a success, although again if you’re ever a kilometer underwater, you have bigger problems than a broken watch.