I2S from old laptop?

[njepitt]

I have a slightly crazy project, which I would like input on - especially if anyone has tried this already. I am using a Linux setup on my main computer, which also passes internet service on to the LAN, with IP addresses given by avahi. The stereo is in another room, with audio duties being provided by an Airport Express, using raop_play as the necessary software to stream audio. This works pretty well on the whole, and since I am unable to get a Squeezebox down here in Brazil it is probably the best option I have available commercially for connecting the stereo to my computer.

But this is diy, right? Here is the idea. The world is full of laptops that no longer have working batteries, or don't run the latest version of windows, or whatever. I am considering opening up such an old laptop and pulling off an I2S signal (probably from somewhere on the soundcard, if I can locate it...) to be sent to a DAC. The laptop needs to be able to run a minimal linux kernel (I plan on using gentoo, although it makes little difference) but doesn't need to store large quantities of music at all - just to pass on what it receives over the LAN. Of course, all this is possible using a USB output, but it seems like it would be better to send the I2S directly to the DAC chip rather than to convert to USB and then back to I2S before DA conversion.... The main advantage would be to have flexibility (and diy fun!) in the DAC itself, having the possibilty of 24bit audio and so forth. Of course, it would have to be a pretty old and worthless laptop, because i may well kill it trying to pull off an I2S signal...


Has anyone tried this? It seems unlikely I am the first to think of this, so if anyone has experience or ideas I'd be very happy to hear about them.

[tritosine]

those laptops have codec chips ( ) no seperate DA, you could only tap i2s before toslink transmitter, then you have something like 5-10 ns jitter embedded in spdif signal (forget bout 16bit) coming out of some noisy enviroment.
Not worth considering.

[Scrappydoo]

Have you looked at the beagleboard?

Outputs i2s.http://beagleboard.org/

[tritosine]

avr32 kits are WAAAAAAY cheaper than that once you dont need fancy smanchy video stuff but 100mbit lan and usb.

[phofman]

I do not think laptops internals offer a significantly cleaner environment than desktops. Noise on their analog outputs is basically comparable to that of integrated sound cards on desktop motherboards.

An old NTB will feature codec with AC97 links, a newer NTB will have a codec linked to the south bridge via Intel HDA protocol. None of those are directly I2S compatible.

[Scrappydoo]

Originally posted by tritosine
avr32 kits are WAAAAAAY cheaper than that once you dont need fancy smanchy video stuff but 100mbit lan and usb.

I haven't seen the avr32, where can you buy one and how do we get I2s from it?
Thanks.

[njepitt]

Wow. I woke up and found all these responses...

Originally posted by tritosine
those laptops have codec chips ( ) no seperate DA, you could only tap i2s before toslink transmitter, then you have something like 5-10 ns jitter embedded in spdif signal (forget bout 16bit) coming out of some noisy enviroment.
Not worth considering.

OK. If there is no DA chip then my original idea is dead in the water.... At least using the USB output should be possible, right? (Although much less appealing from a diy point of view) Would your remarks about a noisy environment apply here also? What about jitter?

Originally posted by Scrappydoo
Have you looked at the beagleboard?

Outputs i2s.http://beagleboard.org/

Yes, I really liked the look of this. The problem is that importing one into Brazil is expensive. (70% import taxes on top of the value of the board *and* postage/packing...) I had the idea of using an old laptop while fishing around for a cheaper alternative.

Originally posted by tritosine
avr32 kits are WAAAAAAY cheaper than that once you dont need fancy smanchy video stuff but 100mbit lan and usb.

Originally posted by Scrappydoo


I haven't seen the avr32, where can you buy one and how do we get I2s from it?
Thanks.

Yes, could you explain further? Perhaps this is the cheaper alternative I was looking for....

Thanks

Nigel

[njepitt]

Originally posted by phofman
I do not think laptops internals offer a significantly cleaner environment than desktops. Noise on their analog outputs is basically comparable to that of integrated sound cards on desktop motherboards.

An old NTB will feature codec with AC97 links, a newer NTB will have a codec linked to the south bridge via Intel HDA protocol. None of those are directly I2S compatible.

Well, I wasn't planning on using the analogue outputs. (In my original idea, now apparently dead, I was planning on pulling a digital I2S signal out of the box). What would you think of using the usb output, if I had an appropriate USB DAC, or a USB-I2S converter or something? (As I mentioned above this is less appealing from a diy point of view...)

As a further query, what would be the principal offender for generating noise? The PSU? Hard drive? Perhaps one could reduce noise by pulling out or deactivating parts not needed for this application. (Which is pretty simple compared to normal laptop business, it seems to me...)

Thanks

Nigel

[tritosine]

http://www.eetasia.com/ART_880046265...P_2193bf2b.HTM

on noise issue : DC-DC converters...

[Pano]

this one?

http://www.atmel.com/dyn/products/to...p?tool_id=4102