combine analog and digital audio in one connector to enable both audio options "natively"

[moosdev]

By using a regular 3.5mm TRS phone socket and a LED instead of the exclusively optical TOSLINK connector it's possible to provide optical and analog audio (with a Mini-Toslink or 3.5mm TRS cable, respectively) in one connector (and consequently gets rid of the DAC requirement if analog audio is needed).

I've come across that convenient fact when I first dug through the MiSTer (github-)project and its wiki.
The IO addon board for it has an 3.5mm TRS phone connector (BOM: J2, BOM+schematics for further review is accessible on the linked github) which does exactly that by using a LED (BOM: LED4) behind the connector on the PCB.
And apparently this is something which is/was used in other commercial products.
(I have an assembled IO-Board on hand and can take a close-up shot of the connector and LED behind it, if needed for clarification.)

I believe the only thing to keep in mind is that the LED has to have the correct wavelength and brightness. From what I could gather from the TOSLINK specification the wavelength should be around 650-660nm. As for the brightness rating I couldn't find a specific value, but it should obviously be bright and stable enough so that it can drive the optical signal over different cable runs, at least up to spec. There's an official support thread for the MiSTer IO-Board at atari-forum.com, where some values get thrown around (apparently 32-326mcd@650nm should be safe/optimal according to one post).

I just wanted to call attention to this, maybe it is a reasonable suggestion that could be integrated in an updated revision of the board (and probably the enclosure too). If you will make more, that is!

In any case, thank you for your work and for sharing it too!