Synthesis Studios

Continuing on a previous post, we’re still tearing apart the Nike + iPod Sport Kit. By using one as a sacrificial device, we popped it open and took a look at the top and bottom — so much to learn! We’ll quickly review the turnaround Apple went through to get the devices out the door, we’ll take a look at the inside of the receiver, and then, finally, we’ll spy on the negotiation between the iPod and the Nike + iPod receiver.

What’s really fascinating to us, in product design terms, is that if you look at the date on the back, the date printed on the PCB is 20060624 — June 24, 2006 and we received the sport kit on July 17! That’s amazing: Apple is able to push out a final version of the PCB, assembled, and ready to go, to consumers in 23 days.

If we poke around the front of the receiver, we’ll all notice a Nordic nRF2401AG which is a single chip 2.4GHz GFSK transceiver implementation. So that’s how they transmit to the puck in your shoe. Wait — transmit? They only need to receive from the puck, right? Interesting.

Revisiting the pinout of the iPod connector, we soldered some 24 AWG wire onto the serial ground, serial TX, and serial RX pins; this lets us intercept all messages going between the receiver and the iPod itself. We rigged up our oscilloscope, set the trigger properly, and plugged the receiver into the iPod. Next, we measured the “size” of a bit, and guessed that the devices talked to each other at 57.6 kbaud encoded at 8N1.

Then came the magic of Python. With a simple script that looks something like:

#!/usr/bin/env python
import serial
serial = serial.Serial( ‘/dev/ttyUSB0′, 57600 )
while True:

c = ser.read()
print ord( c )

We wired the serial pin with data going from the receiver to the iPod into our test DB9 cable, started the script up, plugged the receiver into the iPod, and held our breath:

255 255 255 85 3 0 1 2 250 255 85 …

If you take a look at the iPod accessory protocol (as documented by the iPod Linux team), a block of data is headered with 0xFF 0×55. And our data reflects that!

Watch this space. There’s much more to follow…

This entry was posted on Friday, July 21st, 2006 at 1:57 pm and is filed under Synthesis. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.