How do you make an HDMI audio extractor?

I know they can be purchased for cheap but I was wondering how do you make one? Is it as simple as soldering a Digital Optical TOSLINK to the audio pins on an HDMI port or does it require much more?

My RCA receiver is old and only has 3 composite video inputs and 1 output, 1 S-Video input and 1 output, a bunch of RCA analog jacks inputs and a couple RCA outputs, one Digital Coax input, and one Optical input. I need to extract digital audio from the Wii U and my laptop.

Any help would be highly appreciated!

 

There are no audio pins on the HDMI port, the audio signal is sent in the "unused" areas of the video signal. An HDMI audio extractor needs to decode the video signals, extract the audio data islands and repackage their content as SPDIF. HDMI receiver chips usually implement most of this process, but building your own extractor with one probably isn't worth it.

 

Oh ok. I found one on amazon.com for $30 including shipping. I guess I'll just get that one.