Wristwatch PCB Swaps Must Be In The Air

Are we seeing more wristwatch PCB swapping projects because more people are working on them, or because we saw one and they’re on our mind? The world may never know, but when it comes to design constraints, there’s a pretty fun challenge here both in fitting your electronic wizardry inside the confines of an injection molded case, and in the power budget to make your creation run on a sippy straw of battery power.

Just this morning we came across [Joey Castillo’s] sensor-watch project. He chose the Casio F-91W as the donor wristwatch. It’s got that classic Casio look of a segment LCD display capable of displaying hours, minutes, and seconds, as well as day and date. But the added bonus is that we know these have decent water resistance while still providing three buttons for user input. Sure, it’s less buttons than the pink calculator watch we saw [Dave Darko] working on earlier in the week, but which would you trust in the pool?

Replacement PCB sized to use the same battery contact and CR2016 for power [via @josecastillo]
We see that [Joey] also chose to use the ATSAML22 microcontroller and sheds some light on why: it includes a built-in segment LCD controller! If you’re a peripheral geek like us, you can read about the SLCD controller on page 924 of the datasheet (PDF), it’s a whole datasheet onto itself.

The sensor part of the sensor-watch is a flex PCB breakout that allows you to swap in whatever sensor fits your needs. The first to be reflowed at [Joey’s] bench is a BME280 humidity sensor, which is most obviously useful for the included temperature measurements, but maybe it could also alarm at moisture ingress? [Joey] says you can swap in other parts as long as they’re in the QFN or LGA size range. We think an IMU is in order since there’s a lot of fun interaction there like the watch reacting to being positioned in front of your face, or to take tap-based inputs.

We think beginning with a donor watch is brilliant since pulling off a case, especially one that keeps water out, is 97% of the battle. But when your UI is unique to the watch world, sometimes you need to start from scratch like this wooden word clock wristwatch.

19 thoughts on “Wristwatch PCB Swaps Must Be In The Air

  1. Interesting, is there a graphic B/W LCD that fit’s into F-91W case? Add a little RF (NRF24, rfPIC, BlueCore, ESP8266, etc) and things could quickly become pretty interesting.

    I think, there is only few steps left to the creation of popular multiarch (may be even Arduiino IDE compatible?) platform, even better than TI ez430-Cronos.

    1. My Casio watch has a 3 character dot matrix for day of week and mode display. The rest of the watch function are okay for the usual 7 segment display.

      The stuff on your list are going to burn power and give the button cell a hard time.

      1. Monochrome LCD’s without backlight does not burn significantly more power more than same 7 segment displays. They are the same things, just with different layout of electrodes. There is also e-ink displays that does not eat anything when idle. RF stuff is not necessary power hungry WiFi or 2/3/4/5G. Typical wireless mouse build around NRF24 lasts many months on a single AA battery. I see no problem to have a watch where you have to replace or charge battery once a month or two along all that watch-like SmartGarbage crap that needs recharging every single day.

      2. A 3 character dot matrix could be really useful. I’m not sure yet what for, but the community will come up with something. And, as a child of the 1980s, I still think they are cool and futuristic :-)

  2. I’d like to see one of those where the hacker re-utilises the solar cell.
    Obviously, not a G-shock, unless someone is committed enough to make their custom PCB shock proof as well!

    1. Haven’t see a watch with solar power panel since my last Seiko LCD watch. The problem is that the rechargeable battery is expensive and hard to find these days. My Casio watch lithium coin cell battery life outlasts its.

      The only other watch I have that has a solar panel is a $5 Chinese watch mostly for gimmick. The case is horrible and non-water proof, but large enough for a PCB replacement.

      1. I have a Casio Waveceptor that I got, I think, in 2006, some great deal, I think I paid $20. Certainly not more than $30. I got it for the “atomic watch” but it just happens to have a solar panel.

        It still uses its first battery. I take it off every night, and leave it by the window, important for syncing up anyway. I don’t overuse the backlight. One time, I activated the feature that turned on the backlight so it automatically lit if you made a gesture like you were reading the watch. That was the first time the indicator showed less than full.

        When I landed in the hospital two years ago, the watch somehow came with me. But with no chance to recharge and me using the backlight, the charge got low. I splurged on a G-Shock, I had some gift cards.

        So the Waveceptor has been retired. It’s looking old, and the battery has seen a lot of use.

        I’ll get another one, but few or no solar powered being sold.

      2. Is the solar panel connected? I have a cheap solar calculator that stopped working. When I took it apart I found the ‘solar panel’ was just an unconnected dummy; the calcuator was powered by a standard lithium button cell.

      3. There are many G-Shocks that are solar. Anything with Tough Solar on the panel is solar already, such as the GW-6900, GW-5600, GST-100 among others.

        The 5600 and 6900 are affordable and readily available in the market as standard, entry offerings.

      4. I’ve been rocking a Casio solar waveceptor wvq-m410 imported from japan for the last three years or so. It’s interesting since it’s a quartz watch but has analog style hands and the entire watch face is a solar panel. I find it’s stayed charged just from normal use and haven’t yet had to manually leave it in the sun to charge. The verdict is still out on how long the rechargeable battery will last, and by the time it needs a new one I may just retire it and upgrade to a new watch anyway.

        1. I was under the impression that the solar cell tops it off, but the battery starts with a lot of oomph. So with time the charging becomes more significant. I can’t remember if I read something, or got that impression from use.

          Mine has outlived the estimated battery life, by five or ten years (I forget the estimate) but it needs more charging as time goes in.

          If you’re outside a lot, in short sleeves, the watch will see more sunlight than long sleeves with lots of clouds.

          I got another Casio, the one with the altimeter and such, and I never used the backlight other than to try it, and the battery was dead within five years. No solar there.

    2. A)

      flexible plastic solar cells do exist, so integrating into watch strap should be ez.


      1) you can cut bigger solar panel and use it instead of / under existing cover (plastic) glass,
      water jet can cut it,
      i did not try cuting solar panels with laser, so i do not know if it will work

      2) you can then solder very thin ” bus bars ” into a solar cell in a such way that produced electricity can move,
      this depends on geometry of your cut in 1) !

      3) you can cut solar panels and use multiple pieces in your watch strap,
      watch strap on metal watches is made of nice cuboids anyway ;)

      you can cover your solar panel with transparent epoxy ( translucent epoxy = less light but colors! ) so it will be more sturdy,
      you can even polish your epoxy layer if it gets scratched.
      but you need strap from solid material like metal or wood so it wont flex and crack your panel, epoxy.


      you do not need rechargeable battery, you can just use solar panel to lower your consumption
      even add flat capacitor array ( ceramic capacitors ) to help your nonrechargeable battery when watch does not get enough light.
      you can find capacitors with lower height then cpu used in this article, ez

      how many capacitors can you pack in area required for that top
      or that left programming connector ?
      a LOT,
      just redesign connectors
      you can even place DIY conducting pads on top of processor to act as a programming connector.
      just connect pads on top with pads on side with small bent wires ( pcb is just epoxied wires anyway )

      and you will have place for your capacitor bank

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