Sensor Watch: a board swap for the classic Casio F-91W wristwatch | Hacker News Reader

Sensor Watch: a board swap for the classic Casio F-91W wristwatch

sensorwatch.net

153 pointsthunderbong59 comments

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I'm currently wearing a F-91W with one of these installed. Here's what I have running:

* Clock

* Sunrise and Sunset times

* Die roller (d2, 4, 6, 8, 10, 12, 20, and 100)

* Stopwatch

* Temperature sensor

* 36-hour temperature log

The die roller was the main one that I was excited about, but the sunrise/sunset seem useful while hiking or backpacking, and the temperature sensor and log are great for camping use. Great job by @josecastillo all around!

Curious what you use the die roller for?

It's honestly kind of nice for trivial decision-making. The d2 displays H/t instead of 1 and 2, so it's an actual coin flip. Other than that, I just wanted it for the novelty, pulling it out during D&D was hilarious.

I thought you were using it for dice man-esque decision making :) https://en.wikipedia.org/wiki/The_Dice_Man

Die are great for decisions you don’t care about. Assign options for eating lunch, say, to numbers, roll the die, if you feel the need to fudge the result now your actual preference is revealed.

For fans, I recently ran into am interactive state chart diagram for the watch.

https://casio-f91w.pages.dev/

Cool - has the original firmware been reverse engineered / disassembled?

Maybe it doesn’t even have firmware.

There's no FW on it as a programable microcontroller would be far too expensive, it's just glue logic die under a black resin blob, optimized to the absolute bare minimum number of transistors, which you can easily reverse engineer as the die shots are now public[1], but it doesn't help you since you can't reprogram it, it's just to learn how it works.

FWIW, your cheapo basic electric toothbrush without any smart features on it, has a 4-bit Swatch microcontroller[2] from the 90's, with 4K ROM, 320 bytes of RAM (flexes-biceps), for driving the motor, blinking the LED and monitoring the battery level, and this is how you write SW for it[3], and the 90's IDE & toolchain still works on Win 11 today, wild.

[1] https://zeptobars.com/en/read/Casio-F-91W-OKI-quartz-watch

[2] https://www.emmicroelectronic.com/product/multi-io/em6607

[3] https://www.emmicroelectronic.com/sites/default/files/produc...

Calling Ken Shirriff ...

Multiple layers of metal and a 2006 date make reverse engineering this die more of a challenge then I want.

Sorry, I didn't get what you meant, what makes 2006 a challenge for reverse engineering?

2006 is too modern for me since the features are very small. I usually reverse engineer chips from the 1970s.

Looks cool but I couldn't find any use cases or examples, what are the ways people are using this to improve their watch?

I guess there's more info there https://www.sensorwatch.net/docs/watchfaces/

I enjoy this simply to have sunset, sunrise, and moon phase on my wrist. The added precision from the finetune watch face is a nice bonus.

It's a fun and cheap project for anyone just tinkering with electronics.

Like the ben eater kits - it's not really useful, but it's fun to do and then have

Check out the 'complications' section - there are a bunch of additional features you can add - moon phase, timers, TOTP Generator, invaders game and more. https://www.sensorwatch.net/docs/watchfaces/complication/

This would seem more useful on something like one of the calculator watches or I know I once had a watch with a TV remote built in, not sure offhand if that one was Casio, but that'd seem like something more useful to have in a watch.

I had one of those remote control watches, it was a Casio CMD-10 https://www.reddit.com/media?url=https%3A%2F%2Fi.redd.it%2Fn...

It is years since I longed for something with such primal raw visceral yearning!

I need a VCR remote on my wrist!

>I need a VCR remote on my wrist!

Casio: Best I can do is a calculator.

I feel like mine was a different model that was not as colorful, but very similar otherwise. It was always fun to control TVs in public and nobody would know who did it or how.

TOTP generator? I never knew I needed this until now. It's also got a pulsometer which is great. I'm gonna try to hack an asthmometer into it as well.

TOTP generator is more useful if it uses NFC.

If I could make one change to my F-91W it would be to use top right number (normally day) to use as an hours counter in stop watch mode. Right now you can only measure 1 hour.

At the really simple end, I’m using it to prevent my watch from accidentally switching out of 24h mode, and to disable the hourly beep that can be accidentally turned on.

I found this watch because I could not find anything with more than 2 timers. I wanted a watch that has 5+ for cooking. This watch doesn't either, but I'm writing a face in rust to support this case

I also want sunrise/sunset time, random number generator, and hourly beep+30m beep like a ships clock

https://www.thermoworks.com/timestack/

There's a Sensor Watch simulator that demonstrates the features of the various firmware images; this one[1] is running the firmware that shipped with the first boards, and includes a clock, world clock (UTC by default, but customizable by holding the Alarm button), sunrise/sunset, moon phase and temperature. For the sunrise/sunset to work, you'll have to click the "Set Location Register" button, which will prompt for location access.

There are other versions of prebuilt firmware here[2], but my favorite one (even if it's a bit impractical) is the Stargazer firmware[3], whose second watch face can display the locations of the sun, moon and seven planets both in right ascension and declination, as well as altitude and azimuth if you grant location access. We're able to fit a truncated version of the VSOP87 model for planetary motion, right there on your wrist.

[1]: https://www.sensorwatch.net/docs/firmware/simulate/backer/

[2]: https://www.sensorwatch.net/docs/firmware/prebuilt/

[3]: https://www.sensorwatch.net/docs/firmware/simulate/the_starg...

I own the previous version of this. That's all I have to say.

I have one of these and has great fun with it. https://blog.jgc.org/2022/10/pimping-my-casio-with-oddly-spe...

The main thing I want from a watch is accurate time. This doesn't appear to have any sort of synchronization feature.

Casio does make a variety of watches that receive WWVB and similar time broadcasts.

Yep. I tried to go down the wristwatch rabbit hole with a mechanical Seiko but it kept atrocious time. I suppose I could take it to an expert to get regulated but it would still drift.

The casio watches with "waveceptor" / "atomic" radio sync are my favourites now, the feature has become a dealbreaker for me.

I thought tgey were shutting down that signal...

I haven't heard anything about that. Wikipedia says defunding was proposed in 2019 but rescinded

https://en.wikipedia.org/wiki/WWVB

  WWVB, along with NIST's shortwave time code-and-announcement stations WWV and WWVH, were proposed for defunding and elimination in the 2019 NIST budget.[6] However, the final 2019 NIST budget preserved funding for the three stations.[7]

As long as the watch time doesn't drift drastically, does it really matter? Set it once from your atomic source and it will be fine for seconds accuracy. It's not like you're going to be doing the timing for the LIGO experiment or similar with this watch.

But to directly answer your question, since this board exposes some GPIO and digital buses there's no reason you couldn't built a GPS receiver add on that reads the atomic time from GPS satellite signals and sets the watch time. It would be extra bulk and battery drain of course.

I've lived with a computer and a watch that beep on the hour for the last 20 years or so.

I guess it doesn't actually matter, but I feel obligated to investigate when they're not in sync.

Very cool project overall. The only nag being

>Sensor Watch sips single-digit microamperes of power, making this a watch you can wear all year on a single coin cell.

That's a downgrade vs original board.

None of the alternative PCBs, clones and such I have seen so far manage to even match the original.

Is getting into the nanoampere territory really that hard to achieve, with technology that's some 30+ years newer?

This board is an order of magnitude more capable as a general CPU than the original, that's why it takes more power. The SAM L22 processor on it has 32 kilobytes of RAM and 256 kilobytes of code/flash storage vs basically zero memory or programmability on the original. You could easily run micropython, tinygo, johnny five (JavaScript), lua or other high level languages directly on the L22 processor here. It's a fun board for embedded electronics hobbyists. If you've ever played with an Arduino, this is basically one you can wear on your wrist in a classic watch shell.

I don't think this product is for you if you're just expecting a longer battery life watch... and that's ok!

You are comparing a very purpose-built chip in the original watch to a general purpose microprocessor in this design. The original won't have a single extra transistor than it needs, and it won't be operating one Hz faster than it needs to. Not a surprise to me.

And in reality, the real-life battery life of the Sensor Watch will drop further if you actually attach actual sensors to it or (I'd expect) start running your own code on it.

The Movement framework for developing watch faces tries to steer folks toward low power consumption by default; the watch spends most of its time in standby, and a custom watch face only runs code once per loop (which is once a second by default, although you can request more frequent updates from 1 to 128 Hz). This means most watch faces can actually stay under 10 µA as long as they don't need to update too frequently; up to about 16 Hz, power consumption remains decent.

Anecdotally, my daily driver is coming up on 550 days on the same CR2016 coin cell from February 2022, and I think it's on track to make it to 2024. A far cry from the original's 7+ year battery life, but still pretty good considering all it's capable of!

That is really impressive!!! Are you able to do some kind of power management on any attachable sensors as well besides whatever their standby current is?

I'm not sure that it'd be easy to get that -and- programmability, and past about the 6 month per battery swap mark I'd likely rather have more CPU/RAM/flash than more battery life.

>> Sensor Watch sips single-digit microamperes of power, making this a watch you can wear all year on a single coin cell.

> That's a downgrade vs original board.

> None of the alternative PCBs, clones and such I have seen so far manage to even match the original.

Yeah, but it's still extremely impressive given the upgrade in capability. I'm sure a designer has to make major compromises to optimize for battery life to level of the original.

Though, for something like this, it might have made more sense to target something like the Casio W800H-1AV; which is another cheap classic Casio, but it has a bigger battery, more display capability, and a 4th button.

My first thought as well. I have worn this watch every day since 2009. Last year I changed the battery for the first time. I have always thought that it is the perfect form factor to fit some more fancy stuff in there.

In an update on crowd supply, the creator mentioned he got 425 days of battery life, which I feel like is pretty good considering how powerful the CPU is compared to the original!

https://www.crowdsupply.com/oddly-specific-objects/sensor-wa...

I've got a ripoff of one of these Casios that I bought years ago in a market in Chile. I wonder if this board would fit the ripoff...

It's cool, but they could use better base model, there are casios with more items on the display. F-91W is very small.

Maybe not everyone wants to carry grandma's cuckoo clock on their wrist?

Ok, I just wanted to say that certain models would allow more things to be displayed, like W-800H for example. I actually own F-91W for nostalgia, but it's like a boy watch.

Boy watch? Or lightweight and out of the way?

For me, the ol' F-91W is the only watch I can bear to wear.

Of course, depends on the wrist. It just feels very small to me. I alternate between W-217H, which is a bit larger version, or Casio Duro, which feels like ok size for me, but that's analog.

You're being downloaded because "boy" is diminutive in this context. Like real men can't wear small watches. Which is, of course, unnecessary cock sizing.

I use my F-91W as a "banger watch" when I'm outside doing a lot of physical work where it might get banged up or covered in dirt. Accurate, so light you barely know you are wearing it, and cheap to replace should I really bang it up. It has been holding up admirably so far. I love it!

40USD seems a little steep. How much do these things cost to produce?

Well, apparently the person who made it said they can't do another run like the previous as they made zero money off it.

Not zero money; it turned a profit of about $16,000, but it was hard fought. I wrote a detailed post about the economics of the gadget here: https://www.patreon.com/posts/closing-and-on-78683968

Development and reverse engineering probably takes ~500 hours. They probably won't sell more than 1,000 (I'm making these numbers up). Cost for a small run of boards with component placement, with shipping is probably $20-30. They're probably not making much.

Edit: On the crowdsupply page, they mention "As of today, we’ve shipped nearly 1,500 of them. That’s 1,500 boards manufactured by PCBWay, assembled by Cyber City Circuits, and tested, packed and shipped by me personally, plus 1,500 temperature sensor boards hand-assembled by yours truly." Hand-assembly of SMT components is very laborious and not very fun, so that will add at least 10 minutes per board, which adds another 250+ hours of work.

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