Step 16: How to get sound out of the iPod (3)
Pin 21 !
The legendary Pin 21 of the iPod plug.
This pin is connected to ground via a resistor. The value of this resistor determines what the iPod thinks it is connected to.
If you put a 500kOhm resistor here, it thinks it is connected to a "Dension Ice Link Plus" car interface.
For more info on what all the pinouts do, which vary slighly from model to model of iPod and iPhone, check out the table here:
This is essential as it is what is telling the iPod to connect to the Arduino.