Don't people buy things just to destroy them for self-educational purposes? No? Oh... Well here is another breakdown of the internals of a commercial device. You can learn a lot from professionally engineered devices. Hunting for pictures online of the internals of the Nike+iPod pieces were surprisingly dissatisfying. The only set of pictures available were horribly out of focus, so here is a quick set of pictures to show you how the popular Nike+iPod product works.
There is a very interesting paper published by some students at U-Dub in the CS department. They basically tapped into the serial connection on the receiver and figured out how to listen for different foot tags. Not surprisingly the news has harped on this as a 'security and privacy risk'. A malicious person could design a system to listen for specific tags, as a means of tracking people and places (think crazy ex-boyfriend stalker), but it's just as plausible that we could use this commercially available product (CHEAP! $23.15 internet purchase at time of writing) to monitor where my Grandpa is sleeping, where my 4-year old nephew is playing, or I could automatically turn on/off my lights when I enter my office. Where RFID requires you to physically get near a reader, this active foot pod can transmit over 10-20ft. You don't need to think about getting an RFID card out of your wallet, you just let your shoes do the talking.
The Nike+iPod is not RFID or any form of RFID (Radio Frequency Identification) much to the chagrin of news reporters. While the foot pod does transmit a unique ID, it transmits this information actively in the 2.4GHz band. The foot pod transmits a 'hello world I am XYZ' in very short bursts (less than 0.0001 second per broadcast) on one of 80 available channels every time the user takes a step. This active signal can travel as far as 40-60ft (we don't really care to test the range). The publicly available RFID tags operate in the 125kHz or the 13MHz band and are often passive (requiring the tag to be within a few inches of a RFID 'reader'). The Nike+iPod technology is very different from true RFID systems.
There is no MEMs accelerometer! The foot pod was designed to activate a simple piezoelectric sensor to monitor how long your weight is on the foot (the faster you run, the shorter amount of time spent on one foot). This sensor fires an interrupt within a PIC 16F688 (yea! a PIC microcontroller!). I thought there was going to be an accelerometer built in, but this simpler method reduces the device cost considerably ($8-$10 retail dollars) and probably avoids some nasty patent infringements! Companies like Dynastream and PhatRat (hey, they're just down the street from SparkFun!) use an accelerometer associated with a human's gait and movement to determine overall distance, speed, etc.
Enough! Here are the pictures...
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