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You can't go for very long without hearing about the Internet of Things (IoT) in general, and wearables in particular. The biggest segment of wearables is fitness trackers that measure your activity, sleep patterns, heart rate, and perhaps other things. The leader is Fitbit. At DesignCon last week, Patrick Mannion of ClariTek ran through a teardown of a different fitness tracker, the Misfit Shine 2. I have seen teardowns done live before, where the actual device is opened up and broken down on stage, but this was like a cooking program: we got the one prepared earlier.
The overall market for fitness trackers is growing fast, from under 10 million devices in 2013 to a forecast of 135 million in 2018. There are some stormclouds on the horizon for the market though. One is that trackers get used enthusiastically at first and then get left in the back of the drawer (I'm guilty of this, my Fitbit sits on my coffee table unused). There are a number of lawsuits about accuracy, especially of heartrate. The more like a medical device these units become then the more likely it is that they might come under the heavy hand of medical industry regulation. But for now, with just hearrate, they seem to be clear. The biggest challenge from a system point of view is power (or energy or battery life, which all come to the same thing).
The Misfit Shine 2 is designed to look like a very high-end watch. In fact the company, Misfit, was bought by Fossil for $260M at the end of last year. During the acquisition, Fossil said that they plan to introduce some of the Misfit technology into traditional watches this year.
The Shine 2 tracks distance, calories, activity type, and sleep quality and duration. But this isn't a commercial for the device, the interesting stuff is what is inside. To me, the most interesting feature is that they took a different approach from Fitbit and the Apple Watch and didn't make it rechargable. Instead it runs on a single CR2032 coin cell on which it lasts for six months. It seems that this battery has a capacity of 240mAh or so, which is not much.
So exploding the device, at the top level it contains:
The main circuit board contains all the components:
The big way power is saved is that the Ambiq part operates in the sub-threshold region of the transistors, without the transistors ever being fully turned on. Ambiq calls this SPOT for Subthreshold Power Optimized Technology. Operating at 0.5V (instead of 1.5V) can reduce the power by 13X. Going further and reducing the power to 0.3V gives a power saving of 36X. I still find it amazing that the system energy requirements can be reduced so much. The Dialog part has wireless connectivity, and the accelerometers can't be turned off all the time or they can't track activity accurately.
I continue to think that most IoT devices are going to be built using this sort of approach for the time being: standard products integrated onto a little circuit board with a lot attention paid to power consumption. Security is going to be a big challenge since encryption algorithms tend to require a lot of computation and thus a lot of power. But it is hard to provide solid security without using encryption. Not that it is particularly serious compared to taking over, say, a car, but I suspect that your Shine 2 could be hacked in some way over its Bluetooth link (which I think is the only communication channel, unless you also count the touch-sensitive screen and the LEDs).
Here are block diagrams for the two main chips. Both are ARM-based.
If you want to know more about the Shine 2 (buy one and tear it down youself, maybe) then take a look at the full details. The retail cost is $99.