Inside 'Nike+iPod' -- Diaphragm is Used as Sensor

Jul 24, 2006
Chikashi Horikiri and Phil Keys, Silicon Valley
The board, sensor device and button cell battery appeared when the sensor module chassis was opened. We opened the plastic chassis by cutting off the joint around the opening with a cutter knife.
The board, sensor device and button cell battery appeared when the sensor module chassis was opened. We opened the plastic chassis by cutting off the joint around the opening with a cutter knife.
[Click to enlarge image]

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.)

The appearance of the interior of the sensor module: The IC mounted on the left board is Nordic Semiconductor's radio transmitter IC "nRF2402."
The appearance of the interior of the sensor module: The IC mounted on the left board is Nordic Semiconductor's radio transmitter IC "nRF2402."
[Click to enlarge image]
The backside of the interior of the sensor module: An 8-bit microcomputer "PIC16F688" released from Microchip Technology Inc., "sleep/resume" button, source IC, etc. are mounted on the left board. It measures 20 mm in diameter and 3 mm thick.
The backside of the interior of the sensor module: An 8-bit microcomputer "PIC16F688" released from Microchip Technology Inc., "sleep/resume" button, source IC, etc. are mounted on the left board. It measures 20 mm in diameter and 3 mm thick.
[Click to enlarge image]
The appearance of the interior of the radio receiver: The board densely mounted with numerous components is connected to the lower part of the connector block. Nordic Semiconductor's radio transceiver IC "nRF2401A" is located slightly left from the center of the board. A crystal oscillator and a component supposedly an antenna are disposed to the left of the transceiver IC and in the lower right corner of the board, respectively.
The appearance of the interior of the radio receiver: The board densely mounted with numerous components is connected to the lower part of the connector block. Nordic Semiconductor's radio transceiver IC "nRF2401A" is located slightly left from the center of the board. A crystal oscillator and a component supposedly an antenna are disposed to the left of the transceiver IC and in the lower right corner of the board, respectively.
[Click to enlarge image]
On the backside of the interior of the radio receiver, a chip for performing interface processing with the iPod main body is mounted. It is marked with "V132 065K E404G4" on its surface.
On the backside of the interior of the radio receiver, a chip for performing interface processing with the iPod main body is mounted. It is marked with "V132 065K E404G4" on its surface.
[Click to enlarge image]