Add S/PDIF optical output to board

[nikitalita]

Adds optical output to the board. Only increases the manufacture price by 2 dollars due to the remapping of the LED pin to S/PDIF output.

No firmware changes yet to enable this; this is just to confirm my design before I send this off to be assembled.

Major changes:

• The LED still exists, but its pin is now used for S/PDIF output. This means it will blink along with the S/PDIF output. This will necessitate some changes to the firmware to make it not just spew all 1s when loading.
• I had to move the power regulator from the front of the board; it's still fairly close to VSYS
• The volume control lines for the wavetable had to be moved to accommodate a better path for the SPDIF line; these run at 250khz so it shouldn't be a problem.
• Various fixes (fixing model paths, adding the bracket to the render, removing non-existent libraries, ensuring symbols exist in project library)

[RetroLoom]

I love this idea and have been hoping for a good spdif solution for a while now. I wonder if it also might work to do a optical / 3.5mm combo similar to this design for the MiSTer IO board.
https://github.com/MiSTer-devel/Hardware_MiSTer/blob/master/releases/iobrd_6.1.pdf
The LED sits behind the 3.5mm port with an open back and uses a 3.5mm toslink cable or adapter instead.

Also, it could be nice to have just a simple pinout that connects to one of these external TTL boards to have as optional.
https://www.amazon.com/gp/product/B07FJMD7BF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[nikitalita]

I love this idea and have been hoping for a good spdif solution for a while now. I wonder if it also might work to do a optical / 3.5mm combo similar to this design for the MiSTer IO board. https://github.com/MiSTer-devel/Hardware_MiSTer/blob/master/releases/iobrd_6.1.pdf The LED sits behind the 3.5mm port with an open back and uses a 3.5mm toslink cable or adapter instead.

Yeah, that might work, but it's really only something you do if you have limited board space, as in the case of the IO board; the mini-toslink cables are harder to find than the regular ones, and you can't do both digital and analog output at the same time with this.

Also, it could be nice to have just a simple pinout that connects to one of these external TTL boards to have as optional. https://www.amazon.com/gp/product/B07FJMD7BF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

yeah, i might do that after this one is validated, i sent it off to be ordered

[nahimov]

nikitalita, hello! Is there any news about your realisation of this pcb board ? It's very interesting.

[nikitalita]

I had the board made, but I haven't been able to get s/pdif working and I haven't had time to work on this. I'm pretty sure the design is valid and that it's a software issue. If you're interested in this, I'd take a look at the spdif branch on this repo here: https://github.com/polpo/picogus/tree/spdif

[nahimov]

Thank you very much!