Inside 'Nike+iPod' -- Diaphragm is Used as Sensor
Tech-On! tear-down team has torn down "Nike+iPod Sport Kit," a product jointly released from Apple Computer, Inc. and Nike Inc. that can manage workout data such as time, distance and burnt calories as the users run by transferring the data to "iPod nano" with the use of a small sensor module inserted in the Nike's athletic footwear.
A "diaphragm" for electronic buzzers, a common component in electronics, is used as the sensor device. A diaphragm is composed of piezoceramics attached to a metal plate. Although it is usually used for generating sound by applying an alternating current, the Nike+iPod Sport Kit uses it as a sensor device. When a pressure is applied to the diaphragm, a voltage is generated by the piezoelectric effect. Upon detecting this information, the sensor module determines that "the foot has touched the ground."
We examined the board and found that a chip stamped with "nRF 2402G 0612AN" is mounted on it. We confirmed that it is a radio transmitter IC "nRF2402" available from Nordic Semiconductor ASA of Norway (Product page of nRF2402). It is an ultralow-power consumption radio chip operable at 2.4 GHz which is mainly used in wireless mice. Nordic Semiconductor is known as the company that provides "ANT," a protocol stack for the personal area network (PAN) released from Dynastream Innovations Inc. of Canada.
Following the sensor module, we proceeded to tear down the radio receiver. Again, Nordic Semiconductor's radio chip appeared when we opened the chassis. What's interesting is that the radio chip mounted on the receiver was not a device dedicated for reception but it was a transceiver IC "nRF2401A" (Product page of nRF2401A). (See pictures below for details.)