IMO the Casio Oceanus S100 is a better watch in that category - solar powered, radio-controlled, waterproof, no apps or connectivity, but more dressy. However it's JDM only so you have to order it off eBay (or buy it on a trip to Japan I suppose).
I love my JDM Oceanus S100. It is one of only a few watch movements where all hands are individually controllable by their own motor. As you move the crown you select different time zones and the hands spin whatever direction is closest to indicate correct time for the new time zone. It is magical. Also the way all hands magically snap in place when you take the watch out of dark store. 10/10 would buy again. (the steel series does not have this movement).
The Sensor Watch wiki lists several other compatible Casio watches [1] that all came with a Casio Module 593. Several have a metal finish, or even a round case. The module number is etched on the steel back.
All modern compatible watches from Casio are made of plastic: black or chromed plastic. Only some vintage models are in real metal. Vintage watches that came with modules 451, 587, 590 or 595 (maybe more) will also fit a module 593, but you'd still have to source a module 593 for its plastic chassis and other parts.
Also, just the other week there popped up a steel replacement case for sale on AliExpress, which as been confirmed to work fine.
I bought a vintage Casio W-34 (Module 590) just for my Sensor Watch because I wanted one of steel and because it resembled my broken A158W that I had used for years.
There is a very active discord community around the sensor watch. Come join us; https://discord.gg/Rdd9ewREaJ. I'm currently working on adding step counting support to the sensor watch pro. (Also I'd appreciate the help in getting a low power and low computation cost step counter working, which is a bit hard when your battery budget is a CR2016.)
I customized the pulsometer by adding the calibration feature so I could use it as an asthmometer at work. This watch has saved lives and I mean that literally. I also helped maintain the first movement before the migration to the second movement firmware, merged in quite a lot of features.
Joey is one of the nicest maintainers I've ever worked with. The discord community is very nice as well. Haven't been very active nowadays due to life matters but I still monitor the discord and try to answer questions.
Autocorrect is dangerous. My worst autocorrect story is me sending my mom the following text : “hi mom, just wanted to let you know I’m tied up at the moment but I’ll give you acall as soon as I get free.” Which resulted in a text about me being tied up at the moment, promising to give my mom a good buggering when my bondage session was over. Confusion and a good laugh followed, but I am so glad it wasn’t a client.
In context, anyone who needs to understand almost certainly got it. Right? I haven't heard of 'caption tape', but I definitely have seen lots of misspellings of 'kapton' in context. :D
Clicked on this thinking it was about a calculator, so impressed that it was about swapping out the guts of an casio watch and building and uploading the firmware.
Admittedly my watch only gets 1/50 the battery life and doesn't pick up WWV. On the other hand, being able to redesign its face in Emacs and Illustrator and update it OTA makes up for a lot. So does not having to wear a molded polymer bracelet - those things are awful!
What's wrong with molded polymer bracelets? I assume you're referring to the wristband?
I've really only worn one watch and it has a molded polymer wristband, and it doesn't bother me, but maybe I'm missing out on something nicer.
They don't breathe and collect sweat as if moved by a creepy fetish. They also have no style, of course, so you can look like a grade schooler while you itch your way to lasting skin problems.
For dress wear I have a selection of steel link and leather bands to match any outfit, including one steel bracelet I torch-colored myself. For casual wear and exercise I like colorful, inexpensive canvas and seatbelt-weave nylon, which are soft and breathe very well, and wash clean easily after even the sweatiest exertion.
Given the humidity this year, I've mostly stayed in the nylon. With a few carefully chosen solids and stripes, it's easy to accent any outfit, and unlike a dime-a-dozen Apple watch I actually don't mind a pop of bright color that draws some attention to what I wear.
What's the process of adding sensors to the custom motherboard? Based on your watchface config it looks like you added accelerometer. I wonder what other sensors are easy to add. I'd love to have an hrm in mine
The SensorWatch platform supports I2C sensors that fit within the watch's tight power and space constraints - beyond accelerometers, temperature/humidity, pressure, and ambient light sensors work well, but HRM would likely draw too much power for the CR2016 battery.
very cool. casio would make killing building fitness band with 3-4 week battery life in the form factor of f91w. cheap fitness bands are basically already the mass smart watches of our era.
Yeah. This and GShock Move. IMO pretty low effort, I'd want basic smart watch / band functions like full sensor suite, notifications, nfc. Literally just need Casio to copy a miband (which goes on sale for like <30 USD) / or fitbit and slap it in affordable f91w style body. TBH part of me feels sad / thinks JP electronic decline = they're simply not capable. Fingers crossed for day Casio figures out f91w shaped smartband/watch where the buttons can control media or be programmable like pebble. I'd pay 200+ for fancier housing, but not watch+pedometer.
I may have gotten a dud, but the sensor watch pro board Unused had a _really_ bad crystal oscillator. Like, slow by over 30 seconds a day. There is the oscillator fine tune complication but the oscillator I had was way beyond the max adjustment range (32k ppm). Maybe it was just luck of the draw and I should give it another shot but having a clock that needed to be adjusted every few days was unusable.
Reminds me of the Texas Instrument Chronos, which was a watch that existed solely to promote the MSP430. I think it was released around 2013. Looks like it's no longer in production, but you can find them used around $40.
I really like that USB port. It can probably be made to work in both directions (like USB-C). Does it require a special PCB thickness that is hard to come by?
This is a really simple "project" because someone else did all the work! I just had to install the thing and make some tiny code modifications for my taste.
The key to doing things when you're very busy is to do them slowly and not drive yourself crazy with a deadline. When I did the ThinkPad 701c restoration it took me a year!
Got mine yesterday after some back and forth with customs who had difficulties to understand what this is.
Love it so far. I'm really impressed by how simple it is to compile new firmware. It even keeps settings between firmware updates!
I think this watch is the right balance between smart and dumb. No distractions and connected features. But supports virtually any offline feature you can think of.
TSA: "Sir, are you wearing the terrorist watch?"
You: "no no, it's a modified terrorist watch, it now has more features!"
https://www.spiegel.de/international/world/al-qaida-s-watch-...
https://www.watchesofespionage.com/blogs/woe-dispatch/casio-...
Typically I wear this watch instead: https://blog.jgc.org/2025/06/the-discreet-charm-of-infrastru...
looks like we have the same taste. I wear that one in summer (with short sleeves) and sensor watch the rest of the year
brb gotta buy a casio lineage watch now
IMO the Casio Oceanus S100 is a better watch in that category - solar powered, radio-controlled, waterproof, no apps or connectivity, but more dressy. However it's JDM only so you have to order it off eBay (or buy it on a trip to Japan I suppose).
I love my JDM Oceanus S100. It is one of only a few watch movements where all hands are individually controllable by their own motor. As you move the crown you select different time zones and the hands spin whatever direction is closest to indicate correct time for the new time zone. It is magical. Also the way all hands magically snap in place when you take the watch out of dark store. 10/10 would buy again. (the steel series does not have this movement).
It's also got an integrated bracelet so harder to swap out the bracelet for a leather watch strap (if that's your thing).
The Sensor Watch wiki lists several other compatible Casio watches [1] that all came with a Casio Module 593. Several have a metal finish, or even a round case. The module number is etched on the steel back.
All modern compatible watches from Casio are made of plastic: black or chromed plastic. Only some vintage models are in real metal. Vintage watches that came with modules 451, 587, 590 or 595 (maybe more) will also fit a module 593, but you'd still have to source a module 593 for its plastic chassis and other parts. Also, just the other week there popped up a steel replacement case for sale on AliExpress, which as been confirmed to work fine.
I bought a vintage Casio W-34 (Module 590) just for my Sensor Watch because I wanted one of steel and because it resembled my broken A158W that I had used for years.
1. https://www.sensorwatch.net/docs/#need-to-buy-a-watch
You: “No no not the terrorist watch, I’m wearing the Obama watch”
ICE brownshirt: “same thing”
(https://iknowwatches.com/casio-f-91w-classic-watch-review/)
Love to see the simulator screenshot. I was the one who added simulator support for the custom LCD: https://github.com/joeycastillo/second-movement/pull/26.
There is a very active discord community around the sensor watch. Come join us; https://discord.gg/Rdd9ewREaJ. I'm currently working on adding step counting support to the sensor watch pro. (Also I'd appreciate the help in getting a low power and low computation cost step counter working, which is a bit hard when your battery budget is a CR2016.)
I customized the pulsometer by adding the calibration feature so I could use it as an asthmometer at work. This watch has saved lives and I mean that literally. I also helped maintain the first movement before the migration to the second movement firmware, merged in quite a lot of features.
Joey is one of the nicest maintainers I've ever worked with. The discord community is very nice as well. Haven't been very active nowadays due to life matters but I still monitor the discord and try to answer questions.
> Since I bought the optional accelerometer add on it's necessary to put in place a little piece of caption tape
This should be _Kapton Tape_ https://croylek.com/pages/kapton-tape?srsltid=AfmBOoqVfkbfaW...
Argh. Motherducking autocorrect!
Autocorrect is dangerous. My worst autocorrect story is me sending my mom the following text : “hi mom, just wanted to let you know I’m tied up at the moment but I’ll give you acall as soon as I get free.” Which resulted in a text about me being tied up at the moment, promising to give my mom a good buggering when my bondage session was over. Confusion and a good laugh followed, but I am so glad it wasn’t a client.
In context, anyone who needs to understand almost certainly got it. Right? I haven't heard of 'caption tape', but I definitely have seen lots of misspellings of 'kapton' in context. :D
Clicked on this thinking it was about a calculator, so impressed that it was about swapping out the guts of an casio watch and building and uploading the firmware.
I do also like calculators: https://blog.jgc.org/2025/04/just-one-more-calculator-bro-ju...
I was thinking it’d be about a musical keyboard.
I have been reluctantly holding off hoping they will come out with a dot matrix or epaper screen. Neither will probably ever happen but I can dream.
There is this one: https://gitlab.com/_Pegor/kepler_fw
That is exactly what I want! Thank you for sharing the link.
Oh this looks awesome
I absolutely loved my Pebble. It was so amazing in its own niche.
You do know that Pebble is back from the dead?
https://repebble.com
> git clone --recurse-submodules [...]
Small improvement but it should get the clone and the submodules at the same time.
Admittedly my watch only gets 1/50 the battery life and doesn't pick up WWV. On the other hand, being able to redesign its face in Emacs and Illustrator and update it OTA makes up for a lot. So does not having to wear a molded polymer bracelet - those things are awful!
What's wrong with molded polymer bracelets? I assume you're referring to the wristband? I've really only worn one watch and it has a molded polymer wristband, and it doesn't bother me, but maybe I'm missing out on something nicer.
They don't breathe and collect sweat as if moved by a creepy fetish. They also have no style, of course, so you can look like a grade schooler while you itch your way to lasting skin problems.
For dress wear I have a selection of steel link and leather bands to match any outfit, including one steel bracelet I torch-colored myself. For casual wear and exercise I like colorful, inexpensive canvas and seatbelt-weave nylon, which are soft and breathe very well, and wash clean easily after even the sweatiest exertion.
Given the humidity this year, I've mostly stayed in the nylon. With a few carefully chosen solids and stripes, it's easy to accent any outfit, and unlike a dime-a-dozen Apple watch I actually don't mind a pop of bright color that draws some attention to what I wear.
What's the process of adding sensors to the custom motherboard? Based on your watchface config it looks like you added accelerometer. I wonder what other sensors are easy to add. I'd love to have an hrm in mine
There are details on the sensor part here: https://www.sensorwatch.net/docs/sensorboards/ and reference designs here: https://github.com/joeycastillo/Sensor-Watch/tree/main/PCB/S...
The SensorWatch platform supports I2C sensors that fit within the watch's tight power and space constraints - beyond accelerometers, temperature/humidity, pressure, and ambient light sensors work well, but HRM would likely draw too much power for the CR2016 battery.
very cool. casio would make killing building fitness band with 3-4 week battery life in the form factor of f91w. cheap fitness bands are basically already the mass smart watches of our era.
Did you see this one? https://www.casio.com/europe/watches/casio/vintage/product.A...
Yeah. This and GShock Move. IMO pretty low effort, I'd want basic smart watch / band functions like full sensor suite, notifications, nfc. Literally just need Casio to copy a miband (which goes on sale for like <30 USD) / or fitbit and slap it in affordable f91w style body. TBH part of me feels sad / thinks JP electronic decline = they're simply not capable. Fingers crossed for day Casio figures out f91w shaped smartband/watch where the buttons can control media or be programmable like pebble. I'd pay 200+ for fancier housing, but not watch+pedometer.
I may have gotten a dud, but the sensor watch pro board Unused had a _really_ bad crystal oscillator. Like, slow by over 30 seconds a day. There is the oscillator fine tune complication but the oscillator I had was way beyond the max adjustment range (32k ppm). Maybe it was just luck of the draw and I should give it another shot but having a clock that needed to be adjusted every few days was unusable.
this is definitely not normal. I have the non pro version and it loses like 3s per year.
Reminds me of the Texas Instrument Chronos, which was a watch that existed solely to promote the MSP430. I think it was released around 2013. Looks like it's no longer in production, but you can find them used around $40.
I really like that USB port. It can probably be made to work in both directions (like USB-C). Does it require a special PCB thickness that is hard to come by?
I have wanted this for forever. My dream watch is the F91-W, but with weather as well. I cannot wait to try this out.
It's an amazing project. I wear mine every day. Highly recommended.
This, is how to enjoy your retirement. Hope we see lots of other fun projects like this from you John, a very enjoyable read. :)
This is a really simple "project" because someone else did all the work! I just had to install the thing and make some tiny code modifications for my taste.
Was there ever a version of this that would run a full blown DOS?
Very cool! What's the expected battery run time?
See: https://www.crowdsupply.com/oddly-specific-objects/sensor-wa... Answer: 1 to 2 years. My previous watch from the original blog post is still running on the original battery.
Thank you, John.
Coincidentally, your web site https://jgc.org/ is truly a lovely example of https://news.ycombinator.com/item?id=44613625 which was just discussed today as well.
Love your behind the screens stuff!
Thanks! Glad you enjoy https://behind-the-screens.tv. Those videos were an enormous amount of work because of all the original research behind them. I do have one more I'd like to do about this film: https://www.rottentomatoes.com/m/defense_play_1987 One day perhaps!
Oh I don't doubt it! I was thinking how does such a busy man have time for this... but we always have time for passions and side projects :)
The airwolf one was funny, since it was a childhood favorite, and what a funny little typo they had there.
When watching the video I was thinking to myself, could this series have influenced my future interests in ways I didn't even know? Fun.
The key to doing things when you're very busy is to do them slowly and not drive yourself crazy with a deadline. When I did the ThinkPad 701c restoration it took me a year!
Old Thinkpads were truly glorious machines. Top notch engineering and materials.
Mine has been running for over a year now and the battery's voltage is still nearly nominal.
is any Linux version? I'm not using brew
Windows, macOS and Linux instructions here: https://www.sensorwatch.net/docs/movement/building/
Brew run on Linux just as well as on MacOS.
It’s actually the default package manager for uBlue distros.
I’ve used it as my only package manager on Linux for a few years and I love it.
Got mine yesterday after some back and forth with customs who had difficulties to understand what this is.
Love it so far. I'm really impressed by how simple it is to compile new firmware. It even keeps settings between firmware updates!
I think this watch is the right balance between smart and dumb. No distractions and connected features. But supports virtually any offline feature you can think of.
Respect.
This is a brill project
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