The evolution of the world’s thinnest watch, the CST-01

We wanted to recount the evolution of the design of the CST-01 from early CAD sketches to fully working “design validation units” made from real production parts.

February 18, 2013
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7 minutes

In January, Jerry O’Leary and I launched a Kickstarter campaign (currently <3 days to go) for the world’s thinnest watch, the CST-01. This is a watch we have worked on outside of project work while here at IDEO. On IDEO Labs, our aim is to share our process and give our readers an “under-the-hood” look at some of the things happening here at IDEO and, occasionally, beyond our walls. With that in mind, we wanted to recount the evolution of the design of the CST-01 from early CAD sketches to fully working “design validation units” made from real production parts.  Click through for the full story and our process images:

About a year ago, I started tossing some ideas back and forth with Jerry about what we could do with the segmented font Nick Zambetti and I designed for Bug Labs  (part of an open design experiment we launched here on IDEO Labs). The font we designed was for segmented E Ink screens, which are flexible, robust, and ultra-low power screens. These display qualities are unlike any other technology, and I had always thought something interesting could be done that really took advantage of these properties. This idea had been stewing since we finished our Bug Labs project in January 2009, and the catalyst that got me thinking about our font again was a new microcontroller I’d discovered from Epson with built-in E Ink drivers and a real-time clock.  What if we could use the font to create a “word clock” that spelled the time out when stretched out on a flat surface, but then displayed the time in numeric format when bent onto a wrist? That was the first incarnation of the design.

The first Illustrator mockup and first paper prototype:

Initial Rendering

One of the challenges of this design was that the electronics would need to drive 439 segments. This was outside of the capabilities of the Epson system-on-chip (SoC) that we were considering, and would require multiple driver chips, thereby increasing the complexity of the design. We decided to look at the challenge again, but this time taking the capabilities of the Epson SoC as a constraint. This meant only 64 available segments. With only 64 segments, the idea of doing a word clock was no longer possible, so we focused on what it might be like if it were just the numeric time. This also meant rethinking the design of the font — one of the most fun and challenging aspects. Here’s a sketch of the first iteration:

First draft of segment design

We went back to the drawing board to see what this new direction might mean now that we no longer were committed to doing a “word clock”:


Here’s an analog style concept:

Analog Style Concept

And a Progress Bar concept:

Progress Bar

And Progress Bar prototype:

Progress Bar Prototype

simple_segment_1 packiaging_2

There was still something about the curves in the original font that we wanted to preserve, though. Sometimes inspiration comes from the most unlikely places. I saw a keypad like this and thought, “Why not try to widen the center segments?”:


After a lot of tweaking and segment counting, we arrived at our final segment map using 63 of the 64 available segments:


We were starting to think about branding as well. What should the watch be called?  We made a word jumble of the subset of letters the font could display. It looked like this:

Screen Shot 2013-02-18 at 4.13.16 PM

We live in Chicago, so the idea of our company being called “Central Standard Timing” (CST) just made sense. We started with the segments because of the E Ink display. E Ink only uses power when updating, so when the watch is on the shelf and not using power, we can keep a static image. We liked the idea of displaying the name (CST) on the face of the watch until the unit is charged for the first time.

IMG_0478 IMG_0479

At one point, one of us remarked: “I’m liking these designs, but I can’t tell if it’s too much like a ‘hand belt.'” From that moment on, the idea that it was a “hand belt” was a constant reminder that the design needed to change. To get a tactile feel for how flexible the display was, we used an old Esquire magazine that used a segmented E Ink display on its cover.  The magazine display looked like this:


Around this time, several factors led us to start using a stainless steel band. All the components were flexible, but we didn’t want to encourage people to bend them too much, and the display was flexible enough that someone could easily wrap it around his or her and close a buckle (as shown earlier). But we’d also become obsessed with the idea of designing the world’s thinnest watch. And although adding a buckle or clasp wouldn’t count in the overall measurement, it felt silly to have a clasp that was thicker than the rest of the watch. We took some E Ink display material from the Bug Labs project and tested it on some spring steel strapping:


It was immediately clear that this was the best direction. We looked into a lot of other details. How do we charge it? What are our power options? How do we set the time?  Things started looking more similar to where we are today: all another

We wanted to find batteries that were as thin or thinner than our display and could power the watch for years. After a few dead ends, we ran across Thinergy batteries. Another IDEOer, Garrett Winther, made us this great Arduino-controlled bend-testing rig shown here:

We would charge the batteries, run them through 1,000 bends, then using another Arduino board set-up, test the battery capacity.  The Thinergy cells lasted through 4,000 bends at a radius of 22.5mm and still held about 85% of the capacity that the cell held on first charge. This bend is far more extreme than the watch should ever incur in normal use. During everyday wear, the battery would be fine.

The next unknown was the band. It needed to be flexible, resilient, non-ferromagnetic, and made from a kind of metal that does not commonly react with people’s skin. Stainless spring steel was our choice. We researched different ways of creating a pocket for the electronics in the stainless band. Our first explorations included looking into both multiple layers and stamping a pocket into the band. We then came across photochemical etching, which only required a single piece of metal and allowed us to control the tolerances very well. We worked with a local photochemical etcher to get our first prototypes:

The raw material:

The raw material

The etching machine:

The etching machine

Our first bands!

Our first bands!

It was now time to bite the bullet and have samples of our custom E Ink display fabricated! We had samples of displays and electronics assembled and shipped to us. From there, we sent out final drawings for circuit boards, display segments, and screenprinted masks (and couldn’t wait until they arrived).

A final paper test before releasing the display drawings:

A final paper test before releasing the screen drawings

Programming the display modules after they arrived:

Programming Jig

Prototype Parts

Prototype Parts

In our conversations with E Ink, we became aware of an opportunity to show off working units at CES 2013. This deadline became our new goal. We were able to make more revisions of the front mask (the one shown above simply would not look right in our tests) and used an adhesive that could be laser cut for rapid iteration on assembly techniques.

While very different than what our actual manufacturing assembly method will be, the novel assembly method we finally landed on (with the help of IDEO model shop wizard John Grimley) was to first tape all the parts and layers in place, then use a FoodSaver to vacuum seal them all together. We would then take the bagged watch assembly and heat it in a pot of water to set the adhesive.


It took a few experiments, but we finally got the “recipe” right:



We 3D printed our base station, applied a filler primer, sanded, painted, and fitted it with a mini Arduino board and our charging circuit:





With our working DVUs, we were ready to take some photos and film the Kickstarter video:


Thanks to fellow IDEOer, Adam Geremia, for his incredible photography and video skills, and Breanne Heath, our hand model.

We’ve been working on this side project for over a year now, so a lot has been skipped over, but we hope this provides a good background story of the evolution of the CST-01 watch.

There are less than 4 days left at the time of writing, so for those interested, back us on Kickstarter.

Also, thanks to all our current backers, we are extremely grateful for your support.

Dave Vondle