Gamecube digital audio interface board

Another PCB project!

I want to make separate post from my other PCB project. While I was designing the YPbPr to VGA converter board (reference here), I realized that I would only need a 4cm x 5cm board. However the PCB fab house I deal with will charge me the same price for a 5cm x 5cm board.

That means that I still had 1cm x 5cm of PCB space to do something! Alright then, I always wanted to add TOSLINK audio out on my Gamecube but I didn't want to search and buy an obsolete TC9231N chip. They are big, hard to find and need a lot of supporting components...

That's why I wanted to use the DIT4096. It can replace the TC9231N and does not require the HEX inverter originally needed on the TC9231N. The only problem is that this IC is only available in TSSOP package. You need a PCB to solder it on or else you're going to screw things up!

The goal of this is to be able to offer a more up to date design of the digital audio mod so people don't have to struggle in finding obscure and obsolete parts. I took the time to improve over the original solution by providing a breakout PCB and the following features:
- Switching power supply with voltage input support for 6Vdc to 12Vdc (LM2674)
- All parts can be soldered by hands (TSSOP is the hardest)
- Small form factor that will fit behind the DVD drive.
- Up to date parts so they can all be found easily.

This mod is great because you don't need to have the Gamecube Component video cable. You don't even need to have a Gamecube revision with the Digital A/V port! Every cube can have this mod as you can tap on the internal digital audio signals.

The DIT4096 is really a flexible chip and it happen that it's totally usable with the Gamecube in hardware mode(Putting this chip in software mode offers a greater range of configuration but you need to have it configured by a microcontroller or any other programming circuit). The left-right sync polarity is correct for the Gamecube by default so no hex inverter needed. It is even possible to have 3 different value of oscillator to output 48KHz sample audio. However the design of this project is locked to 12.288MHz, you'd have to change the configurations of the clock pins to adjust the pre-scaler according to your oscillator. Incidently, you need to change the layout of the schematic to configure those pins. 12.288MHz is a pretty standard value and at the time of design, it was the cheapest oscillator of the 3 values.

So 1cm x 5cm of space to integrate all this:

Challenge accepted!

And here it is:

OK it looks messy because all the layers are shown in Eagle.

The crude rendering of the topside of the PCB looks good:

So everything fits except for the oscillator that does overlap a little up and down of the PCB. It was a compromise to be made in order to select an oscillator that can easily soldered by hand without the use of a hot air solder gun. Other oscillators don't have exposed pads on their sides; they are smaller but harder to solder for most people. Anyway the whole thing fits on the required space so why bother!

Bottom side of the PCB:

Yes I made a typo on the inscription... I remember well that I added this thing at the last minute because I wanted to have some sort of writing to identify the PCB.




Here's the basic disposition of the board:


There was little space left for solder pads for Inputs and Outputs... They are not cleanly aligned but they will do the job right. This board was designed to output to a 5V TOSLINK transceiver (TOTX178, TOTX177, TOTX179). You could add a few resistors in order to use a COAX output instead of TOSLINK. You can refer to this site of rmore info on this.

As like my other project, I will not release any files as I want to make sure that the design is working good.

I will have 10 PCBs and only one of them will be useful to me. Once everything is confirmed working, I will release the project files and sell PCBs (populated or not) if people are interested.

 

Looks good! Waiting for the result when you get the PCB

 

Could be interesting. I've got a Gamecube on its way to get the mods repaired.

 

I'll be sure to post my results as soon as I get the PCB.

 

any chance for the same thing for wii,snes or n64?

 

Maybe, for the SNES. The DIT409 seems far more versatile than the CS8405A both in hardware mode. I'd have to cross-check the CS8405A datasheet along with the wiring for the SNES digital audio mode to determine if the DIT4096 could be configured in any way to accept input.

From what I've read, N64 digital audio would be a little trickier as there is less info about it. I read that the DAC chip used it the BU9480f. Was there ever a digital audio mod for N64 that was succesfully made? It's probably possible to do it and I'll probably try it on my N64 as well!

I don't think it's possible to output digital audio from the Wii. From what I've seen the DSP gets fed chunks of data that can be composed of multiple portions that aren't audio. The audio is decoded and converted to analog signal internally in the DSP. The 3 signals needed to produce SP/DIF stream (SDATA, BCLK, LRCLK) will never leave the DSP, then it's not possible to tap onto the signal traces to capture digital audio data. Maybe by drilling the chip and tapping onto an internal metal trace but I don't feel it's worth it. Decode raw data coming from the main bus and into the DSP is theorically possible but I don't think no one wants to get into that sort of stuff only for digital audio!

 

Ok, I received the PCBs last friday and so proceeded to start soldering components on the YPbPr to VGA board... only to find out I screwed up the wiring of the voltage regulators ICs...

I made a new design and submitted to the PCB fab house. I should get them in 2 weeks... I took the opportunity to update the GC TOSLINK board to make it smaller by removing the whole switching regulator. If you mount the board inside, you'll be able to find a +5V source. So no regulator is needed.

 

I know this is a very old post but... did you manage to create a digital audio transcreiver for the gamecube without using the obsolete Toshiba part?