Long story short: I've been to the US a few weeks ago and I thought I'd pick up a new Xbox 360 250GB while I was there, seeing as those are hard to find in China. I assumed its power supply would accept both 110V and 220V (like my PS3 and most modern PCs and laptops.) Well, it did not.

Of course, I did not just plug it in and watch explode. I first opened up the power supply (not an easy feat, let me tell you) and only plugged it in after noticing the board inside had "250V" written on it, with a check mark next to it. Not sure what that meant though. It still blew up after I plugged it in.

I already had a plan B from the moment I bought the Xbox: the power supply output 12V and 5V, much like a regular PC power supply. So I bought a (mini) ATX power supply and went online to see if I could find the pinout. Plenty. When I plugged in the ATX power source, I measured the voltage on a few pins, but got nothing. Then I remembered the fact that an ATX power supply does not really turn on until the PC tells it to. This is done by shorting pin 14 of the ATX plug (green wire) to ground (black, any will do.) Once I did that, I got all the power I needed.

The pinout on the Xbox side was harder to come by. I had found a few for the old Xbox 360, but none for the new slim model. Fortunately there were some hints on the PSU's board:

Yellow 12V
Black GND
Red 5VSB
Blue PS_ON
Gray RSENSE

I thought I'd check what I could get away with: I connected the yellow wire from the Xbox to the yellow wire of the PSU. Same for the red wires, and black wires, matching the colors. Then, I turned on the power supply by connecting the green wire on pin 14 to a black wire. I pressed the button on the Xbox: success!

Having the power supply turned on all the time was not something I liked though. So the next step was to get the power supply to turn on together with the Xbox. By measuring the voltage I saw the blue PS_ON wire being pulled up (~3.3V) when the Xbox wants to turn on. In order to do this, the Xbox needs some power though. This is done by the red "5VSB" wire. The "SB" stands for Stand By. This means that the red wire from the Xbox must not be attached to the red ATX wires, but to the purple wire on pin 9.

This page explained how: use a transistor or optocoupler that will connect the green ATX wire to GND when the blue Xbox wire goes up. I had no optocoupler lying around, or so I thought. I then noticed the blown up power supply on the table. There were some things on it that looked a lot like optocouplers. Sure enough:

The datasheet for the EL817 can be found here.

So, pin 1 of the optocoupler (the pin near the dot) will be pulled high, to ~3.3V. We want to give the LED inside about ~1.2V, that leaves 2.1V for a resistor. At about 20mA this means we need a V/I=R 2.1/0.02= ~100 Ohm resistor. 100 Ohm = 10*10, 10 times 10 to the power 1: we need a resistor with Brown, Black, Brown rings. Luckily I found one

I had everything I needed:

Yellow (Xbox) - Yellow (ATX)
Red (Xbox) - Purple (ATX)
Blue (Xbox) - Resistor - Optocoupler pin 1
Black (Xbox) - Black (ATX)
Optocoupler pin 2 - Green (ATX)
Optocoupler pin 3 - Black (ATX)
Optocoupler pin 4 - Black (ATX)
Gray (Xbox) - unused

I had no idea what the gray RSENSE wire was for, so I just ignored it and it worked fine! Once I got everything figured out, I opened up the ATX PSU and removed all the wires I didn't use. Important: there was a brown wire that got connected to a orange (3.3V) wire IN the ATX power connector. So after cutting of the connector I had to connect the brown wire to 3.3V somewhere inside the PSU.

And all it cost me was an ATX power supply and 1 blister. Not bad

UPDATE: Here's the schematic for the whole thing:

Inspired by this page on NAS-Central, I ordered a USB sound card on TaoBao (15 RMB including delivery!) and plugged it into my LinkStation. A quick dmesg showed that the device was detected, but not recognized.

The NAS-Central page mentions that some kernel modules are needed to get USB audio to work, but of course, the device does not have these modules by default. After googling for a few hours I still could not find any precompiled modules that matched my LinkStation's kernel version, 2.6.22. I decided to jump in and try to compile the modules myself.

So how do you compile kernel modules?

Well, first of all you'll need the correct kernel sources, but that's easy: Buffalo provides them. Download the linux-* package that matches your NAS.

Now you need a compiler. Turns out Buffalo uses CodeSourcery so we best stick to that as well. Get the pre-compiled cross-compilation toolchain here. Select "ARM GNU/linux" and the operating system that you will use for building. No need to download the toolchain source.

Before we can compile the modules we need a kernel configuration file. Some Buffalo source packages seem to include it (the file is called .config and is hidden because of the leading dot) but the one I downloaded did not include one. Copy this file into the root of the folder where you've extracted the Buffalo sources. This .config file most likely has all support for audio disabled so we'll enable it by adding CONFIG_SND=m (or check whether there's a CONFIG_SND present and change that to =m). The 'm' tells the make file to build it as a separately loadable module, instead of building it into the kernel. (Since I didn't want to change the stock kernel, I had to build loadable modules instead.)

Now the good part starts: make modules

The make file should notice the new CONFIG_SND directive and ask you about the specific sound related modules. Make sure you answer 'm' to all of 'em. You don't need them all, but figuring which you need/don't need is too much work.

When make is done we need to 'install' the modules, but not in our host/build system of course! Use the INSTALL_MOD_PATH directive to copy the built modules into a separate folder: make modules_install INSTALL_MOD_PATH=/tmp/MyModules

When done, copy all the files from /tmp/MyModules/lib/modules/2.6.22.7ownkernel/kernel/sound (recursive) to your NAS. Now comes another the tricky part: loading the needed modules. The module you need is snd-usb-audio and snd-pcm-oss, but before this one will need you'll have to load a couple of others. The normal way this is done is to move the modules into the NAS's kernel folder and issue a depmod -a to update the module dependecies and a modprobe snd-usb-audio to load the module with its dependencies. I did it the wrong way: using insmod to load each module by hand, and trying to figure out the order in which to load them by trial-and-error. Eventually, insmod snd-usb-audio.ko loaded without complaints.

Last step: create the device nodes. As per the NAS-Central page:

cd /dev
addgroup audio
mknod -m 660 mixer c 14 0 ; chgrp audio mixer
mknod -m 660 mixer1 c 14 16 ; chgrp audio mixer1
mknod -m 660 dsp c 14 3 ; chgrp audio dsp
mknod -m 660 dsp1 c 14 19 ; chgrp audio dsp1

I am now able to stream music using mpg123, madplay, mpd (all installable using ipkg.)

The sound quality of that 15 RMB sound card sucks though

Here's the final .config file I used to build the sound modules.

I've just finished my first app and have published it on the market! The app is very simple: it shows the current air quality in Beijing, as measured by the US Embassy. Scan the QR Code on the right and my app will pop up in the market app.

(project page on Google code)