Tear Down: Wearable training system gets it half right
The hardware design makes perfect sense. The software leaves a lot to be desired.
I usually try out every product that I tear down. Sometimes I find that the product is useful, and sometimes not. The subject of this month's Tear Down, the Nike SDM Triax Elite training system falls into the latter category. And that's unfortunate because I really wanted to like this product. Let me explain.
If you're not familiar with the Nike SDM Triax Elite, it's a four-piece set that you use/wear while walking or running. As shown below, it consists of a watch, a piece that attaches to your shoe, a piece that straps to your chest, and a piece that connects to your PC. The shoe and chest attachments give real-time responses to the watch through a wireless connection, so you can tell how far you've gone and how fast, what your heart rate is, and so on. Then when you get home, you download that workout information wirelessly to your PC to log the workout.
In theory, that sounds great. The only problem is that I couldn't get it to work properly. The hardware seemed to do it's job flawlessly, but the user interface designed into the software just wouldn't let me do simple operations to track my workouts. I consider myself a fairly astute user, so I assume if I didn't have the patience to figure out how to get it to work, neither would lots of other people.
Now I'll get off my soapbox and describe the hardware design, because from that perspective, it's an excellent design. The product was designed for Nike by Dynastream, which is gaining a great reputation for products of this sort. The SDM Triax Elite was actually the first in a series of products from Nike/Dynastream.
The design starts with a Texas Instruments MSP430 microcontroller on each of the four components. Oddly, it's a different 430 in each instance. That tells me that the designers did their homework and got just the right part for the application.
As you can see from Figure 1, the watch contained an MSP430F135 REV N. I thought it was peculiar that the revisions go all the way up to N, but I was informed that such occurrences are not uncommon. In the case of this MCU, most of those revisions were done internally at TI, so designers likely never knew about them. Only three revisions were made public.
According to Adrian Valenzuela, TI's MSP430 product marketing engineer, "It's not uncommon for a device to release at Rev. J. On these MCUs, the things that generally have the most issues are the serial communications interfaces, where it might have some timing skew, or there might be a bug in the timers. For example, maybe it misses a count or it just doesn't work as expected. In these early 13X and 14X devices, the ADC (analog-to-digital converter) had a number of issues. This is an older device, and that adds to the number of revisions because there's been so much time to find all these bugs. That's typical for the whole industry, not just us."