OTM-02 Is A 3D Printed Wristwatch


We love looking at roll-your-own wristwatch projects. Getting a project small enough to carry around on your wrist is a real challenge. But we think the OTM-02 wristwatch really hit the form factor right on the mark.

OTM stands for Open source Time Machine. It’s the work of [Hairy Kiwi] and he managed to bring the guts of the watch in at a thickness between 6.5 and 7mm. That includes the LCD, PCB, piezo diaphragm, and the battery. The PCB itself is a four-layer board built on 1mm thick substrate. It’s running an EFM32 (ARM) microcontroller which comes with hardware USB support. The little door sitting open on the side of the 3D printed enclosure provides access to the micro USB connector which can be used to charge the 150 mAh battery inside. That may not sound like much juice, but if you set the display to show minutes only [Hairy] calculates a battery life approaching 175 days. If you just have to have the seconds displayed you can expect about two weeks between charges.

Like the name says, this project is Open Source.

[Thanks Liam]

27 thoughts on “OTM-02 Is A 3D Printed Wristwatch

  1. Wow, first hobbyist (having now looked at the site, I think hobbyist is probably far from correct…) project I’ve seen that’s using the Energy Micro uCs. We had the sales team in at my office a few weeks ago, and they have an impressive range of devices.

    I’ve got a dev kit for one of their beefier processors sat in my drawer as a result of their visit, this might be the time to start looking at learning how to drive it.

    EM provide an insane amount of support for these devices, from pre-rolled code examples, to an IDE wrapper that gives instantaneous access to datasheets and the like, along with making importing existing examples into your IDE an absolute dream.

    Can’t help but sound like a bit of a fan boy, I’ve never seen a company put so much effort into making getting up-and-running so easy.

    1. You’re so right Tom. The support Energy Micro provided me as a newbie embedded enthusiast, initially via support.energymicro.com/home prior to the forum.energymicro.com kicking off last year, has been nothing short of superb.

      This origins of the OTM-02 project started life on an Olimex MSP430 dev board connected to a 4×40 alphanumeric display some years ago, before migrating to an EFM32 STK, via a STM Primer2. It’s true that my abilities weren’t up to doing much, especially on the MSP430, but it was the fact I achieved something on the Primer2 with its ARM core, (with considerable assistance from the bare metal project one of the Primer2 forum users published, I hasten to add) that led me to keeping a close eye on ultra-low power MCU developments in the ARM world. That in turn led to my discovery of Energy Micro’s offerings.

      I can genuinely say however, despite the awesome ultra-low power credentials of the EFM32 range, if it weren’t for Energy Micro’s excellent, never-mind continuously improving support and training, I’d still be battling to get my project going on one of their devices while also keeping a closer watch on the embedded market for the next best thing. The fact is, the Energy Micro forum has developed an almost family-like feel to it, the support staff are incredibly talented and knowledgeable engineers and those I chat with, both on and off forum are all genuine enthusiasts themselves – so count me in to your fan boy club.

  2. [Full disclosure: I work for Energy Micro]

    Awesome! Happy to see hairykiwi’s project on hackaday, this is certainly a milestone for any electronics enthusiast! We got in touch with hairykiwi sometime last year on our forum and he has been sharing his progress ever since. I’m simply flattered by the design and build quality of this project and looking forward to the updates.

    @JoSSte In the last update he said that he wants to wrap things up and upload the up to date design files, so be patient, it’s gonna be fully open source.

    @Tom Probably because we are hacker types as well and hate when things are stealing time from coding. Actually, we are allowed to tinker/hack things 1 day/month and we created a watch mockup in a couple of days that also ended up on Hackaday. Thanks for the feedback! :)

    1. Hi Adam (And sorry to detract from the relativeness of the thread…)

      This is an attitude that certainly shows, from what I’ve seen. I’m fast approaching the limits of what I can achieve in terms of processing power with 8 bit AVRs, and have been weighing up getting to grips with the EM system Vs the Atmel UC3-A3.

      Again, having seen your demo in-house, I know which one I’ll be looking at first, even if it means leaving my beloved AVR studio IDE behind! Hopefully I’ll have something to post up here soon, even if it’s just an intro for the ‘Duino guys.



      1. Hi Brendan,
        I’ve literally just started using open source tools for building firmware in the last few days, so perhaps the following is of interest:

        Energy Micro (EM) have a good, paced tutorial in the form of AN0023, which you can download here: http://www.energymicro.com/downloads/application-notes.
        As I was instructed to do, I suggest you read and understand it thoroughly. It’s not that its an overly complex install process, there are just plenty of details you need to ensure are correct. Regardless of which gcc based IDE you use, AN0023 is worth a read in helping to understand the major components that go into any (open source) toolchain.

        Personally, I found Eclipse+gcc to be a little ugly and unwieldy, (that’s not very objective, I appreciate) but it does work. Having used and admired the cleanliness of IAR EWARM Kick Start (32KB code size limit) for a number of years, I was very happy when I discovered emIDE, (with close integration with Segger’s JLink GDB server, a separate download) via this thread on the EM forum:

        The first post there contains an emIDE project file that can be used with the EM EFM32 Gecko Development Kit (DVK). Further down page one, I’ve posted a link to an edited version of the first file for use with the (smaller and cheaper) EM EFM32 STK dev board. Both these project files require an associated makefile in addition to the project file (vs standalone project file). Until em IDE is itself cross-platform capable, (currently Windows only) the makefile solution probably ensures the best cross-platform usability of any source code, despite being an extra file to maintain and keep aligned with the project file.

        As of emIDE version 2.02a (130403), the following examples are included in the download: SAM7 and CortexM (generic start projects), ADuCM360 (blinky and ADC/UART project), AT91SAM7S64 evalboard (blinky project) and STM3240G evalboard (blinky and SWO-printf project)

    1. Obviously it’s the shell that’s printed. You’d be a bit optimistic to think they’d printed a mechanical wristwatch, you can’t make those out of plastic with any method! But it’s been printed to house the open-source watch that’s also quite an amazing hack. Have I mentioned I want one?

  3. Absolutely love those EFM32 micros. I was never aware of the fact that you can fall in love with microcontroller brand before I’ve tried orking with gecko. The standard API architecture is great, the ability to wake up from sleep on loads of different triggers – priceless.

    1. Your laser cut strap sounds like a beautiful idea! I’ve no idea which wood would provide longest-lasting flexibility, but it’s worth an experiment – have a go and lets hear how it goes! Now this reminds me – I saw an absolutely stunning, functional wooden watch movement and case in the Watch and Clock Museum in Vienna, so wood really shouldn’t be underestimated in terms of it’s usefulness.

      Regarding my design, I don’t particularly like the how the leather strap blends (or rather doesn’t) into the case, but it’s all about working on priorities in the knowledge that some aspects can undergo more rapid and continuous refinement at a later stage. And that’s one of the really cool aspects that (DIY) 3D printing brings to OSHW based manufacturing – if you don’t like a design, you’re free to modify it and print you’re own version.

      I did in fact begin working on a 3D printed strap back in October last year – inspired by some of the articulated objects designed by PrettySmallThings and available on Thingiverse: http://www.thingiverse.com/PrettySmallThings/designs
      But I quickly came to realise that a 3D printed strap would likely involve reworking the strap to case attachment method, and more especially, require even more time to generate all the interlinking joints – so yes it’s in the pipeline, but it’s not a priority.

  4. How difficult would it be to modify the faceplate to include a solar panel to charge the battery? I’m thinking along the lines of some of the old calculators that had a small strip of solar panels and still work (with no battery replacement) decades later.

    1. Nice idea – and also worth an experiment! There are considerable, (in terms of time) but not insurmountable challenges to implementing your idea, which at the very least will require changes to the case design and additions to the PCB design. But the EFM32 is probably well suited to controlling the kind of charge pump circuit a solar cell would likely require. I should add that I’m not familiar with latest generation solar (PV) solutions, nor the exact circuit required, so more research is definitely required. It could also be that there are other more efficient ways of charging the battery about to come onto the market, such as conversion of thermal or mechanical energy. Regardless, the whole field of micro-power generation is set to become quite exciting in the next few years.

      It’s also worth mentioning that In it’s current form, EVERY single component in OTM-02 can be bought in individual quantities, from at least one of the global electronics suppliers. This was, and remains, a core objective of the project. To achieve that has taken considerable patience, in waiting for the miniaturisation of mainstream electronic components – the battery, surprisingly, (approx 12 months ago) and the display, (literally weeks ago) were among the last items to meet the core criteria.

      So as the design currently stands, and as mundane as it might first appear, I believe OTM-02 might actually represent a very real milestone in the world of consumer electronics.

    1. That sounds like crap (or perhaps a typo). I’m not sure what Watch Platform you’re referring to but my TI Chronos seems fine. It sat unused in a drawer for about 9 months and when I grabbed it the time was correct.

    2. I completely agree with the requirement for ‘reasonable accuracy’; and It does sound like you got very unlucky with your TI Chronos.

      IIRC, many digital watch manufacturers specify something in the order of ±20 – 30 seconds per month for typical run-of-the-mill models. But of course we’ve all come to know, and now expect, they perform significantly better – perhaps ±3 – 5 seconds per month, or better.

      So day-to-day accuracy is very high on my list of priorities, but for those times you do need to adjust it, I implemented a feature in an early development code that involves waiting only until a multiple of 10 seconds rolls around, rather than having to wait for ‘the next minute’ before setting (hacking) the watch.

  5. Well it’s a real honour to see my little project make it to the pages of this esteemed site – Thank you Hackaday! And another big THANK YOU to everyone who, by way of their support and encouragement, has helped get it this far. It’s had it fair-dinkum challenges all right, but for me, the project speaks more about how empowering the internet can be, than the accomplishment itself.

    Speaking of accomplishment, looks can be a deceiving. Although it’s steadily taking shape, as with most challenging projects, it’s about 90% complete, and 90% to go – and it’ll be ready when it’s ready. Equally however, I really do want to encourage people to dive in, start hacking, give feedback on any aspect of the design and throw around ideas about what it could be or evolve into. And yes, this really is just the project of a keen hobbyist with little if any expertise any any one aspect of the design. OK, I did train as an avionics technician 25 years ago, but most of what I learnt I’ve long since forgotten. These days I’m a professional pilot ‘by day’, and ‘by night’ a hobbyist with half a clue about how and what aspect to work on next, a little bit of perseverance and an internet connection for ongoing self-education. And it is only me – so I have to apologise for the frequent delays in publishing to github or the Energy Micro forum.

    There’s still a few tweaks to be made to the prototype case design before I’m happy with it, and confident the DIY 3D printing community should be able to successfully print it ‘straight off the net’. Even then I don’t expect the initial design to function or last as well as a ‘bought one’ so I hope people really will start hacking improvements and variations to the basic case design just as soon as it’s published.

    The prototype PCB was only recently hand-assembled and reflow soldered – at home, using a toaster oven under control of an osPID.com PID controller which, rather appropriately, was hacked to provide a smoother reflow profile than I found I could achieving with pure PID control.

    As of right now, I hope to get some code running on it quite soon. But family and work commitments do and will continue to come first.

    There is a small detail that needs setting straight regarding Hackaday’s post, (everything’s small but important when it comes to watches):
    OTM-02 is the name and model number I’ve given the watch module – the electronics part – just as ‘Lemania 5100’ and ‘Valjoux 7750’ are the names and model numbers of two mechanical movements/calibres that many watch manufacturers might buy-in, to fit to their own case designs. (OK, perhaps the Lemania 5100 is no longer – killed off, but forever remembered.)

    So thats the module name sorted. The DIY 3D printed case design shown in the Hackaday post has, until now been un-named; so lets call it the Tinka – after the cat who’s promoted herself to ‘Director of Quality Control’ during the evolution of this project – and as a salute to all the hackers and makers out there with a strange affliction for DIY watch making – as redundant as watches may be these days.

    As for the ‘MTM’ noted on the case by one keen observer; well ‘Mead Time Machines’ might be a name under which complete watches finished by me are sold. But that’s some time away yet.

    Hopefully that fills in a few details for the meantime. Time now to hack on!

    Thanks again Hackaday!

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