Nano
17 August 2006 - 07:33 pmSo I got an iPod Nano (1GB, black) with a Nike transmitter (i.e., lozenge). They also have special shoes, but I just got a little shoelace-mounted velcro pouch for $5 that does the job.
I asked the guy in the Apple store how it works but he was unable to provide me with any semblance of an answer. It consists of a shoe-based lozenge transmitter and an iPod-based receiver, communicating via bluetooth I presume (which makes the receiver a mighty small bluetooth receiver). The lozenge presumably houses some kind of accelerometer which detects your stride. The question was: how can it calculate distance based only on time and number of strides? I thought that they may have come up with some slick way of doing it, maybe double-integrating the acceleration data to get position (without the constants).
But it turned out to be much simpler. You calibrate it by running a known distance (in my case 0.5 mi with a gps in one hand). It simply divides to determine your stride length. This is a little inaccurate as it assumes a constant stride length throughout. This never happens. Running up- or downhill your stride length changes, as well as when you start to tire. But it is probably close enough. I checked my distance today when I passed the same point that was 0.5 mi during the calibration, and it was right on. And better than running around with a gps in one hand.
