[HN Gopher] Taking a $15 Casio F91W 5km underwater
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Taking a $15 Casio F91W 5km underwater
Author : nnnnico
Score : 326 points
Date : 2025-01-31 11:40 UTC (20 hours ago)
(HTM) web link (www.watchesofespionage.com)
(TXT) w3m dump (www.watchesofespionage.com)
| mrweasel wrote:
| The F-91W is such a fun little watch[1] and people have done the
| weirdest stuff with it. There's a guide to make the mod on
| Youtube[3]. There's also the TOTP in a F-91W[2]
|
| 1) https://www.youtube.com/watch?v=r6REKCs4-1M
|
| 2) https://blog.singleton.io/posts/2022-10-17-otp-on-wrist/
|
| 3) https://www.youtube.com/watch?v=jLmAq0epfrI
| fnordian_slip wrote:
| https://www.reddit.com/r/F91Ws_on_NATOs/comments/f9udxl/the_...
| also deserves a mention here, and /r/f91w for more general
| stuff.
| Cumpiler69 wrote:
| _> https://www.youtube.com/watch?v=jLmAq0epfrI_
|
| FWIW, a correction is required here. Oil-modding a F91W will
| NOT make it a dive watch replacement as the video creator
| claims several times.
|
| A dive watch is designed to be operated at that depth while the
| weak o-rings around the pushers on the F91W will give up when
| you use the buttons. Oil modding on it holds up during a dive
| as long as you'll never push the buttons, so it's more of a
| neat party trick for show than anything to daily drive.
| eadmund wrote:
| Modified by oil-filling, though.
| klabb3 wrote:
| Yeah but.. it's just the way of gases and liquids under
| pressure. Even if you could sustain the pressure with gas it
| would be an unnecessary implosion risk if it's pierced. As long
| as it still functions fully including on the surface, I
| wouldn't qualify that as cheating. More like us biological
| weaklings who need ~1atm can be cheap and skip the liquid/resin
| because if we accidentally end up in space or the deep sea we
| generally have bigger problems than checking the time.
| Liquix wrote:
| easy solution: fill _yourself_ with oil before diving.
| checkmate, nation-state navies
| neutered_knot wrote:
| As depicted in the move "The Abyss".
| https://en.wikipedia.org/wiki/Liquid_breathing
| euroderf wrote:
| Also the aliens in the Sylvia & Gerry Anderson TV series
| "UFO".
| LeifCarrotson wrote:
| I've read that it's possible to breathe oxygenated liquid
| perfluorocarbons, but something about the idea is just
| terrifying to me. I think it's the "fluoro" bit
| specifically that scares me, even moreso than the "liquid"
| part.
| nradov wrote:
| Humans can't really "breathe" oxygenated liquid. Our
| diaphragms aren't strong enough to move sufficient liquid
| in and out of the lungs, so it can only work with
| external mechanical ventilation. This is occasionally
| used as a salvage therapy for patients hospitalized in
| critical care but is totally impractical and unsafe for
| any sort of diving.
|
| In the real world outside of sci-fi movies, any human
| diving much deeper than about 0.5km will have to be done
| in an an atmospheric diving suit.
| Mogzol wrote:
| I think it would have been interesting to send two down, one
| oil-filled and one not and see at what depths they break (or
| don't). The watches are cheap enough that destroying one isn't
| much of a loss.
| EVa5I7bHFq9mnYK wrote:
| So the link to espionage is that a spy diver can dive to -5km
| wearing that watch and the watch will stay whole. ChatGPT can be
| really stupid sometimes.
| mrweasel wrote:
| It's actually two separate articles in one, but they had to
| merge them to make the content work for their oddly specific
| website.
| millitzer wrote:
| The second half of this article would make a great movie.
| jrgifford wrote:
| I might be reading into it, but there seems to be a bit of a
| condescending tone with this comment.
|
| The "oddly specific" website has 191K followers on
| Instagram[1] and has done interviews with Hodinkee, one of
| the most well known 21st century watch magazine/blogs. It is
| not that different from others that hit the first page here
| on HN.
|
| [1] https://www.instagram.com/watchesofespionage/
| mrweasel wrote:
| You reading a bit to much into it. I did check out their
| content before commenting, there's also three previous
| links shared on HN. I was just amazed that they are able to
| have enough content for something that seems extremely
| specific.
| cbsks wrote:
| For watch hackers, there is an alternate PCB with programmable
| microcontroller available for the F91W
| https://www.sensorwatch.net/
|
| I got one for Christmas and it has been super fun to hack on. I
| programmed a new face for mine that displays the current tide
| level, and next high and low tides.
| noja wrote:
| Where did you get the data for the tides?
| cbsks wrote:
| There's an algorithm you can use to calculate future tides
| but it's complex and I wasn't sure it would even run fast
| enough on the watch. I gave up after a few hours and ended up
| generating an array of high/low tide levels and times for the
| next few years. NOAA has all the tide data you could possibly
| want, and an api to grab it.
|
| https://tidesandcurrents.noaa.gov/tide_predictions.html
|
| https://api.tidesandcurrents.noaa.gov/api/prod/
| somewhatoff wrote:
| Casio do have a tide watch, which presumably uses that
| algorithm:
|
| https://www.greatwatches.co.uk/collections/men/products/cas
| i...
| zardo wrote:
| And this approach actually works for inland waters since
| NOAA predictions are accounting for geographic effects.
| (e.g. the tide in Seattle is drastically different in
| timing and magnitude from the Pacific Coast)
| cbsks wrote:
| NOAA publishes the harmonic coefficients for each tide
| station, so if you hard code those constants into your
| program you should be able to generate accurate tide
| predictions. I looked into it a bunch before it started
| to feel less fun and more like "real work".
|
| https://tidesandcurrents.noaa.gov/about_harmonic_constitu
| ent...
| pjpweaver wrote:
| Did you publish your simple solution anywhere?
| cbsks wrote:
| Not yet. I'll clean it up someday. But not today.
| pjpweaver wrote:
| Looking forward! I hope to work on something similar soon
| too, the API solution seems helpful.
| a-french-anon wrote:
| Too bad it doesn't support the F105, aka "F91 with a usable
| light".
| MetaWhirledPeas wrote:
| Casio is phasing out electroluminescent backlighting and
| going back to a single LED, so I would buy an F105 while you
| still can. I've heard it said it was to improve battery life
| and longevity but I've never had a problem with either one.
| homebrewer wrote:
| If they update F91W to include better backlight, then good
| riddance. Their newer models (like A700W) have single-LED
| backlight, and it's excellent (probably better than EL, but
| I haven't used EL in a while). The watch is very thin too,
| unlike EL models.
| MetaWhirledPeas wrote:
| My son has the newer LED model, and the EL looks better.
| The EL watch is equally thin too.
| kevin_thibedeau wrote:
| Before EL they were using incandescent bulbs. So they're
| going _forward_ to LED.
| MetaWhirledPeas wrote:
| Ahh! So there is some improvement at least.
| ozuly wrote:
| I fixed this on my A158 (basically a silver F91) by replacing
| the backlight spreader. Super simple mod and only costs about
| $12. Granted that's close to the cost of the watch itself.
|
| https://www.etsy.com/listing/1448973768/back-light-
| spreader-...
| jgrahamc wrote:
| Yes, it's great fun: https://blog.jgc.org/2022/10/pimping-my-
| casio-with-oddly-spe...
| skrebbel wrote:
| Wow I'm impressed at the developer experience. A reset
| button, flash with `make install`, woa. I've programmed
| plenty pro embedded systems that had substantially worse
| support. Hacky flasher apps, messing around with the power
| source, _definitely_ no USB connector (on such a small board
| even). Super cool!
| cbsks wrote:
| There's even an emulator that is super helpful when
| designing new complications
| https://www.sensorwatch.net/docs/firmware/simulate/focus/
|
| The firmware code quality is good as well. Well documented
| and easy to extend. It's clearly a labor of love.
| steve_adams_86 wrote:
| As I read the article this is exactly what I wished the watch
| could do, and I wondered if there are any around which do it.
|
| I have a free diving watch and always wondered... Why doesn't
| it support tides? If even approximately? I wrote a script to
| check DFO tides once per week and alert me to potentially good
| diving conditions (cross referenced with the 2 week weather
| forecast; it's not super reliable), but I'd love to have a read
| out of the tide right on my watch.
|
| I guess I could do this with my Apple Watch, but I'm so burned
| out on that ecosystem.
| rsaz wrote:
| Casio has a few watches with tide functionality in their
| G-Shock line. Bit more expensive than the F91W, but still
| great watches. They're marketed to surfers, often under the
| G-LIDE name. Here's a thread about some of them: https://www.
| reddit.com/r/gshock/comments/18jpgq5/casio_gshoc...
| nradov wrote:
| Garmin Descent series watches have free diving activity
| profiles and support tides. It kind of "cheats" by
| downloading tide data from Garmin servers via a Bluetooth
| connection to your smartphone so it's not doing any tide
| calculations on the device.
|
| https://www.garmin.com/en-US/p/766516/pn/010-02604-01#specs
| steve_adams_86 wrote:
| I didn't realize you can get these in this price range.
| Thanks for the heads up!
| 10729287 wrote:
| Ironically, something Casio have been struggled with on their
| fancies G-SHOCK GBX-100 few years ago. Tides were based on
| database and not cycles and they were always wrong (contrary to
| the older, more basic, not connected, tides model). I'm a fan
| of tides G-Shock, I got one and sold it fast unfortunately...
| maybe the only time Casio disappointed me.
|
| https://www.watchuseek.com/threads/need-help-gbx-100-tide-gr...
| freeCandy wrote:
| The author is working on a new version with more features:
| https://www.crowdsupply.com/oddly-specific-objects/sensor-wa...
| cbsks wrote:
| I'm excited for the replacement LCD. The stock display has a
| bunch of restrictions on which segments can be active at once
| https://www.sensorwatch.net/docs/wig/display/
| ndiddy wrote:
| Was disappointed that he only brought a modified oil filled watch
| to 5km underwater. Would have been interesting if he'd have
| strapped a stock watch next to it so we could see when it would
| break.
| rhd wrote:
| This video might be of interest to you-
|
| https://www.youtube.com/watch?v=iOT8XU1ss3E (Do Oil-Filled
| (Hydro Mod) Watches Actually Dive Deeper?)
| homebrewer wrote:
| A very similar model (A158 -- they differ only in the bracelet)
| breaks at 200 m:
|
| https://youtu.be/G3iMkeF8qmA
|
| https://youtu.be/sep5Tw-55yw
|
| The timekeeping mechanism keeps working fine, though, it's only
| the display that's busted.
| dnisbet wrote:
| Yep would have loved more on when the watch (unmodified) would
| actually break and also how you would fill it with oil? There
| can't be much space inside, at what point does the viscosity of
| the oil matter? how do you know you've got all the air out?
| aidenn0 wrote:
| I'm assuming they are using mineral oil; I've not filled a
| watch with mineral oil, but I have worked with it. Mineral
| oil is not particularly viscous; some gentle tapping is
| probably enough to get all the bubbles out.
|
| Here's a video of a PC immersed in mineral oil with an
| aquarium bubbler and you can see the bubbles rise fairly
| quickly:
|
| https://www.youtube.com/watch?v=tUBvWXH1hLs&t=110s
| OliveMate wrote:
| I've been stuck down the Casio modding rabbit hole as of late. I
| knew filling the watch with oil ('hydro-mod') lead to a crisper
| display with better viewing angles and increased water
| resistance, but to see a watch with minor splash resistance
| operate as such depths is insane.
|
| Worth mentioning some drawbacks before you get your precision
| screwdrivers out. Doing it will make your watch get stupidly hot
| in the sun, the process can be messy, and sometimes certain
| mechanisms/features can break as a result of it. Best to check
| what others have done before you.
| cenamus wrote:
| Why does it heat up in the sun?
| two_handfuls wrote:
| My guess: higher thermal mass, so over time it can accumulate
| more heat than a non-filled watch.
| iancmceachern wrote:
| I expect it has more to do with thermal conductivity
| Cerium wrote:
| The back will get hot since the oil improves the heat
| transfer from the front to the back. The sun will always heat
| the front, but as long as the heat transfer rate to the back
| is low enough it won't feel hot - your body will absorb the
| heat and reach an equilibrium temperature which feels
| natural.
| kali_00 wrote:
| Notably, there was no attempt to operate the watch at such
| depths. Pressing a side button would be an interesting test, for
| instance. Many "water resistant" watches, rated to a certain
| depth are only rated so, given the not inconsiderable caveat of
| not being able to operated - just looked at. The higher end, more
| expensive models claiming full waterproof ability don't typically
| have such functional restriction.
| protimewaster wrote:
| It seems like actually pressing a watch button at that depth
| would be quite a feat of precision engineering itself. Are ROV
| arms typically that precise that it would be possible to see
| well enough and finely enough control the arm to press the
| button?
| curiousObject wrote:
| Not sure if the buttons function, but the watch is displaying
| time in the photos, for 50 minutes of the descent at least.
| aurizon wrote:
| These watches often have a quartz crystal - the little can would
| crush and the oil would damp oscillations, so they might have a
| laser trimmed RC loop - which would be cheaper as well as crush-
| proof?
| maxglute wrote:
| I just a fitness band in a f91w or w59 body.
| t1234s wrote:
| Any hacks to fix the useless light?
| echelon_musk wrote:
| Buy a W-86-1VQES instead.
| jibe wrote:
| There is one, but requires another Casio watch to borrow the
| backlight from.
|
| https://youtu.be/9-jd_7eXACU
| rsaz wrote:
| n-o-d-e has what he calls a data runner mod which includes
| simply swapping the stock green light with a brighter white
| one. I've had one for years now, and its still not ideal, but
| definitely better than the original:
|
| https://n-o-d-e.net/datarunner.html
| racnid wrote:
| There are some diffuser mods available too that look like they
| would make a big difference.
| ozuly wrote:
| You can buy replacement backlight spreaders off of etsy. I did
| it to mine and the backlight is now usable..
| _tariky wrote:
| I own legendary GW-5000U. It is amazing to see those cheaper
| alternatives are as good as 5000U.
|
| I'm wondering is there any other brend except Casio that has
| watches as amazing as those are.
| franczesko wrote:
| I think Garmin is doing pretty interesting outdoors models,
| however I prefer Casio due to simplicity and... nostalgia
| discreteevent wrote:
| FYI Casio recently brought out a minimalist series of the F-91W
| (same watch - just a bit less chrome on the face) e.g.
| https://www.casio.com/europe/watches/casio/product.F-91WB-1A...
| Mistletoe wrote:
| If there is one thing the original is, it's too flashy. :)
|
| Kidding aside, that looks pretty neat.
| bookofjoe wrote:
| Ooh, these are beautiful:
|
| Blue: https://www.creationwatches.com/products/casio-
| digital-350/c...
|
| Grey: https://www.creationwatches.com/products/casio-
| digital-350/c...
|
| Black: https://www.amazon.com/Casio-Environmentally-Friendly-
| Bio-Ba...
|
| White: https://www.amazon.com/Casio-Environmentally-Friendly-
| Bio-Ba...
| devindotcom wrote:
| Wow, love this. I of course love the classic color lettering
| (which really is quite tasteful) but I'm going to cop a
| "minimalist" black style for more formal occasions!
| jessekv wrote:
| I found one of these while free diving. Wiped it off and wore it
| for several years, until I lost it while free diving.
| wwilim wrote:
| So did I!
| ASalazarMX wrote:
| Why are these so easy to lose?
| verelo wrote:
| *share
| prova_modena wrote:
| The straps tend to break after a few years. Casio G Shock
| straps last a lot longer, despite being very similar. Not
| sure if it is because the F91W strap is thinner or made of
| a less durable material.
| wwarren wrote:
| The circle is complete
| ge96 wrote:
| Awe the Seal kiss, 20,000 Leagues vibe
| __mharrison__ wrote:
| I modded mine with olive oil when I bought it. Pretty
| indestructible.
| dr_kiszonka wrote:
| Is that a real CIA challenge coin? It has what look like strange
| imperfections.
| runjake wrote:
| Looks like it. The imperfections are just glare from the
| lighting.
| jigneshdarji91 wrote:
| > Incredibly, the F91W survives its journey to an official 4,950
| meters--an astonishing 16,240 feet--and back.
|
| Findings.
|
| > 4,950 meters under the surface, the pressure is approximately
| 7,227 pounds per square inch, which is well over three tons
| pressing on the watch. For context, that's a Dodge Ram 1500 or a
| young adult hippopotamus parked on every inch of your F91W. As
| Americans, we'll do anything to avoid the metric system, but
| using scientific terminology, we're talking about a shitload of
| pressure.
|
| Appreciate the joke.
| franczesko wrote:
| The new abl-100, besides more wearable size could have a nice
| tinkering potential
| johng wrote:
| It's amazing how often this comes up on HN... I'll have to get
| one.
|
| https://hn.algolia.com/?q=f91w
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