[Audio line-out] Building a line-out cable

I have seen the long thread about building a video out cable, bu has anyone had any luck building just an audio line-out cable to connect to the dock connector on the iphone?

i have used a dock connector in my car for a while to play my ipod through the car stereo, and I would really like to use the setup with my iphone. Right now, when i plug in the iphone, absolutely nothing happens and the audio still plays through the iphone speaker.

I have tried connecting a 10K resistor and a 1M resistor between pin 10 and ground, and I still get no response when I plug in the iphone. I would be happy to even get the message about the accessory not being iphone compatible. Does anyone know what configuration will trigger this message?

I've opened up the iphone dock and done some testing. the big chip in there is a dual one-shot timer chip, which seems to control a couple transistors which switch pin 10 to ground through one of two transistors (I think one is for audio mode, and one is for serial mode). Anyone have any more information about this? I'm going to keep working with it, but I was wondering if anyone has already figured it out.

I have read about apple's custom ID chip to identify iphone accessories. As far as I can tell this chip is not in the iphone dock, so it should be possible to turn on the line-out signals without it (unless the chip labeled Q1 is the ID chip, but that wouldn't make much sense).

anyway, let me know if you have nay information about this. This is quite a challenge, and I would love to get it working.

Thanks,
Alex

On the dock, there is a resister of 360k between pin 10 (accessory pin) and ground. You can try connecting this resistor on your cable and see if it enables the line out pins 27 and 28.

You could also try a 500k resistor.

Note sure if you need the dual one-shot timer chip. When you plug in the headphones on the dock, it switches of the iphone speaker. Maybe this is what the timer is used for.

See also here.

Btw any trick to open up the dock? Or did you just destroy it for opening?


PmgR
http://iphone-gps.blogspot.com

Yeah, by connecting a resistor between the accessory pin and ground, I got the airplane mode message. So this works, but is not an optimal solution. I'd still like to figure out exactly how the apple dock is working and replicate its functionality.

And yes, my dock did get destroyed during disassembly. If I had another one, i'd find a way to look at the signals on a oscilloscope to figure out what's going on.

Anyone know if this is a legitimate product?
http://www.dealextreme.com/details.dx/sku.11760

There is a chip on the dock responsible for activating the video out or the audio out without switching to Airplane mode.

All the non compatible accessories (without that chip) will ask to switch to Airplane mode.

Search for the making your own video cable effort thread. ;)

Hello Alex,

Also, when you connect the pin 11 to ground, you get the airplane message and activates the audio line-out.

I'm working on the cable for connecting a gps (all tricks and info is around the forum) and also adding audio line-out capabilities, but I'm at a dead point it seems, because every time that I connect the gps to the cable, it stops the ipod playback. So this serial communication through 13 pin stops ipod.

Is it possible to change this action or behavior through a script or something?
Any thoughts?

Thanks.