Super slim wristwatch build


This slmwtch lives up to its name. When the LCD screen is folded back onto the PCB the entire thing comes in at just 2.35mm. That’s including a coin-cell battery not shown above. Wow!

Part of what makes this possible is the specialized PCB design. [Anders] didn’t want to add more thickness than the screen and battery so he make a cutout in the PCB design to accept each component. In this image it’s easiest to see on the two SMD resistor in the upper left. They’re held in a void by the two solder connections. Admittedly this is not going to be a mass-production friendly design. And we have concerts about the long-term stability of suspending components by their leads. But as a one-off it’s fantastic! See for yourself in the video after the break.

The control for the watch uses two touch sensitive pads on the back of the PCB. There is no backlight for the display which can be a problem when trying to read the time while outdoors. We wonder if an ePaper display with similar dimensions is available?


  1. Jay Sebastian says:

    I think filling the voids around the resistors (and other SMDs) with clear epoxy would keep it sturdy and looking cool.

    • roboman2444 says:

      I was just about to say that, you beat me to it.
      Also, since the components are behind the lcd, they might also be able to be affixed to that. Its also probable that the watch will have a back to it, so the skin doesn’t affect the circuitry with sweat or just its normal conductivity. One could also affix components to this part also.

    • nomnim says:

      It’s called potting, funny that we all jump on the same editorial part of the article to comment on.

    • signal7 says:

      not necessary. when using through-hole parts, we seldom pot the assembly after it has been put together. at the same time, though, through hole parts are “suspended” by their leads and that is the only support they receive. i think the design works fine as it is.

  2. Ren says:

    And we have concerts about the long-term stability of suspending components by their leads.

    Are these concerts like Farm-Aid? Have any big name bands or singers signed up to perform? What is the concert schedule? B^)

  3. Pat says:

    They’re not even being suspended by their leads (considering the QFN package and the resistors/caps don’t *have* leads). They’re being suspended by solder.

  4. alsdkghasldkfjsdlgkashrlkjaselthk says:

    If there is no backlight, isn’t the LCD relying on reflected light, much like the LCDs used in calculators, for visibility? Why would sunlight pose a problem?

  5. T Hudson says:

    The TRS-80 Model 100 used the same design to simplify the wiring on its LCD module and I’ve never heard anyone complain about the robustness of that machine. 30 years old and the inverted TQFP drivers are still functional:

  6. Jim says:

    Upper left, upper right, what’s the difference?

  7. Wizzard says:

    If mass-production was a goal, skip the custom through-hole (lol) SMD components and build on a super-thin flexible PCB. That could be epoxied right on the back of the LCD. Custom rechargable LiPo batteries come in capacities all the way down to 5-10mAH, and I know of thin models in particular which were made at 40mAh with near-paper thinness.

  8. Anders says:

    Actually, the memoryLCD is really good even in dim lighting. I would say it looks better than a e-paper (kindle at least) because when a pixel is white, it has this reflective background which seems better at reflecting ambient light back even without much ambient light. It actually looks better than most other reflective segment LCDs. I also like the possibility of fast refresh rates, up to 60 Hz, try that with e-paper…

  9. fdawg4l says:

    Did anyone see this and think “ipod watch”? I often wonder why more manufacturers don’t mimic this clearly desirable form factor.

    • anon says:

      That’s what I’ve wanted for a long time, but it seems only the Chinese are willing to make it. Unfortunately they make it with that shit Chinese OS whose music player is useless if you have more than an album’s worth of music. :-(

      I gave up and bought a Sansa Clip to put Rockbox on. It was back when they were putting the iPod Nano on wristbands but I’m a flamboyant guy. :-)

  10. technomads says:

    The TRS-80 Model 100 used the same design to simplify the wiring on its LCD module and I’ve never heard anyone complain about the robustness of that machine. 30 years old and the inverted, recessed TQFP driver ICs are still functional:

  11. Clockwise says:

    I have a 70’s vintage lcd wrist watch that no longer functions. It might be amusing to re-stuff the innards with something more modern. Not sure this would fit.

    I can remember another watch, even earlier, with LED digits. The PCB broke into three pieces when my Dad was changing the batteries. He tried to superglue the board back together! Good try, but it did not work.

  12. Brian says:

    Another good choice for the screen could be OLED. Very readable even in bright sunlight.

  13. one says:

    Is it some coincidence that the same gecko art is present in Dave’s designs as well?

  14. jpnorair says:

    Neat. If you want yet another display suggestion, look for “reflex LCD.” For this kind of thing, they blow Eink out of the water.

  15. thatdamnhippie says:

    i guess im going to be be that guy….you have concerts??

  16. zokier says:

    I found this snippet to be fairly incredible:

    “With the CR1616 battery, which has a capacity of about 55 mAh, it should last a bit more than 1 year in the digital watch-face mode. And almost half a year in the analog watch-face mode. Calculating with average consumption of around 5 uA and 14 uA in the two modes”

    A MCU running a LCD on a small coin cell gets a year of runtime?! That’s amazing. I wonder if you could get that amount of energy from some kind of joule thief setup, using body temperature or something as a source.

    • jpnorair says:

      You could, but there would need to be some extra metal as a heat-sink. The MCU is completely underutilized in this setup… all it does is wakeup each second and update the display. The display is bi-stable, so it is only using energy when it is being changed.

      • Anders says:

        The display consumes around 300nA just displaying the static image. The MCU still has to keep track of time with a low frequency oscillator so it cannot be shut off between display updates. The EFM32 mcu consumes approximately 1uA with full RAM retention and crystal oscillator running. Most of the consumption comes from the framebuffer update and data-transfer every second, here autonomous DMA and SPI interface helps alot. There is a longer discussion on all the energy saving tricks in this application note:

  17. Very exciting to read all the comments here, great feedback certainly!

    Anders (@andlier) is the main guy behind the hardware design, but we made the concept together and I was mostly working on the software part and the watchface. Designing the hardware took us one day and after the PCBs came back we spent 1-2 days on getting things up and running. We used our company’s monthly hacking day and some after hours for it. Full disclosure, both of us work for Energy Micro as engineers.

    Mass production was certainly NOT our goal, it really is just a hack, pushing the boundaries of Anders’ soldering skills! :) The epoxy for filling the voids sounds like a good idea.

    Also, there is a difference between the Sharp memory LCDs and the e-paper display, although many companies present e-paper in their marketing material (Pebble for instance) when in reality they use memory LCDs.

    The combination of EFM32 and the Sharp display is the key here to extremely low current consumption, but of course the numbers wouldn’t be that impressive if we used more fancy features or wireless connectivity with Bluetooth LE.

  18. Max Power says:

    Suspending components by their leads like that is quite common in mass-produced products. I have 3 boards on my desk right now which are designed exactly like that.

  19. 0xfred says:

    Damn! After seeing so many “business card” boards that are way too thick I was planning to do something similar. I intended to mount a TSSOP MSP430G2452 and some SMT LEDs upside down through a CNC milled board and a CR2012 battery in a cutout.

    I still might, but now you’re all going to think I copied this.

  20. jwestra says:

    Very nicely done. Both the power consumption and the physical layout. Seriously considering to make one of these. Anyone did a low volume cost assessment already?

    • Anders says:

      That would be very interesting, don’t hesitate to ask us if you have further questions about the design! If you want to make it manufacturable, I would recommend just doing a thin PCB with components mounted in a standard fashion. I believe the thickness could be even thinner if doing a flex-pcb glued on the back of the memoryLCD. If going all the way you could then slip the whole thing into a 3d-printed wrist watch case with protective glass on top. And a lid at the back which holds the battery in place. The memoryLCD is a bit fragile so I strongly recommend some sort of protective glass and frame around it.

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