DIY iPod digital out

[rippingdragon]

Quote:

Originally Posted by error401 /img/forum/go_quote.gif Yes. First of all, USB has 'host' and 'peripheral' devices. The host is responsible for mediating the bus and there must be exactly one on each bus (it's also responsible for providing power). <Snip> It's probably possible for a USB host stack to be written for RockBox or iPod Linux (the PortalPlayer CPU in the iPod has a USB port that can be either a host or device) that could potentially allow connection of a USB audio class device for audio playback. You're welcome to try - but tapping the I2S lines is sure to be much simpler. This would be pretty cool though.

Thanks for all of the info. That was massively helpful and what I was looking for from the start.
Two things I did pick up from that are:

1) Re: USB power - I think I found a flaw in the IS2 direct connection approach. The Pico DAC is powered by USB and not by the included battery (this powers the amp section only). Therefore to use the DAC you would need to have the Pico also plugged into a powered USB source/host. Other then cramping the portability, this may also impact functionality (unless it would still work with no audio signal being received from the USB host, just the power).

2) If it is possible to write a hoststack for Rockbox this does sound like the preferable option. I don't think it would be any "harder", it would just require different skills. The advantage to this would also be that is infinitely replicable with minimal effort on all users part (all they have to do is install the new firmware). Also re: power, the Pico would then be drawing power from your iPod and as such this would reduce battery times.

In conclusion I would love for someone to investigate the option of performing a firmware modification that would allow this kind of interaction

 

[rippingdragon]

This thread also happens to coincide with the annoucement of the iPhone SDK. Perhaps an application could also be developed to enable this function on the iPhone

 

[joneeboi]

Quote:

Originally Posted by rippingdragon /img/forum/go_quote.gif 1) Re: USB power - I think I found a flaw in the IS2 direct connection approach. The Pico DAC is powered by USB and not by the included battery (this powers the amp section only). Therefore to use the DAC you would need to have the Pico also plugged into a powered USB source/host. Other then cramping the portability, this may also impact functionality (unless it would still work with no audio signal being received from the USB host, just the power).

For that, you would just make a USB cord that doesn't connect D+ and D-. After that, you'd have to wonder why portability is such a hassle. You'd have to wonder if the chips chosen for the iPod are all that bad and if it's worth the trouble replacing them. Looking at the project from the end result, it seems like it's not all that bad; wire this here and there, wire that there and here. Make your own USB cable, get on what seems to be some kind of donor transplant list to get a Headamp Pico (donor transplant list because it's long, not because Justin isn't doing a great job with what he has to deal with), wire up your iPod's silly small chip to more silly small pads. Are we forcing a cube into a circular hole?

 

[giuliaudio1]

Hello, do you know how I can get an I2S signal from an Ipod Touch ?

 

[Ynis Avalach]

Quote:

Originally Posted by giuliaudio1 /img/forum/go_quote.gif Hello, do you know how I can get an I2S signal from an Ipod Touch ?

You have to open up your iPod, then find your dac chip and solder some wires from the input of your dac chip (I2S input of the dac chip) to some unused dock pins, that's it.

 

[qusp]

well then why not use a D10?? uses the same dac as the pico, but the dac is powered by the battery as well as the amp. so if its as simple as ^^ you say (which I guess it is in theory) then why dont you do it and show us how its done

 

[Ynis Avalach]

Quote:

Originally Posted by qusp /img/forum/go_quote.gif well then why not use a D10?? uses the same dac as the pico, but the dac is powered by the battery as well as the amp. so if its as simple as ^^ you say (which I guess it is in theory) then why dont you do it and show us how its done

Me? I haven't got a D10, nor have I got a D/A converter, well nothing standalone and I wouldn't want to risk my MDS-JB940.
But I just thought about my old portable MD, maybe I can figure out something tomorrow. I think though, that why should I be the one to achieve this, why hasn't someone else gotten this already, because my idea is soley based on theory. I'm definitly no pro, so trial and error

Ava

 

[FallenAngel]

Makes me wonder why... but I guess people will always want to play with their damn iPods

 

[Ynis Avalach]

Guess so

 

[Ynis Avalach]

Now that I've found BCLK, DACLRC and DACDAT on my Mini 2G board I'll try to connect them to something (well some kind of dac which I still have to find, or I'll try to build a SPDIF out for my iPod).
Oh man how much fun...no it isn't! Damn this board is sooo filled with tiny components. Argghh

 

[steven2992]

Couldn't you wire the i2s to the dock in the ipod, and out through a dock cable to something like this: CS8406 connected to an optical transmitter. Kind of bantam cable dac style. A smal box with a dock cable on one side and an optical transmitter on the other.

 

[boomy3555]

I only touched on some of the posts here in this thread, but how do you control the play functions once you get the digital signal from the ipod to the device. AFAIK the digital pins only allow communication between the ipod and a device. It does not send out a digital signal during the playback process. In other words the ipod can only act as a hard drive. it can't play a song through it's digital pinouts When you press buttons and turn the touch wheel the Ipod plays songs through it's headphone out or analog pin outs. not trough it's digital out.

I think that's why this thread was abandoned last year

 

[qusp]

no boomy, you are incorrect; what about the wadia then?? any device that reads PCM or digital audio (transport) has an i2s stream at some point along the way. directly before the dac would be one place to look a digital audio stream that travels along traces in a device is generally i2s; the problem is tapping that and keeping it intact; as i2s is very prone to interference and jitter. any signal that is able to be tapped is likely to need reclocking as well. its obviously doable, but just where in the signal path it is taken from is well guarded info. anyone got a wadia and the modded ipod willing to make a sacrifice for the greater good? ;p sounds easier than it is in reality, but it is most certainly doable, given the right equipment, skill and knowledge

 

[boomy3555]

Thanks.. I understand. I thought that people were trying to use the digital pinouts to get a signal. I understand how you can catch the signal before it gets to the DAC and re-routing it through a separate device such as the Wadia.

 

[steven2992]

look what i found: iLink Music Server
It looks a lot like what we are discussing here.