I would like to add a Toslink input to my dAack!, originally thought this would require a full blown optical to coax circuit (not all that complicated), but after inspecting the dAck! circuit and checking various datasheets it appears that there's a jumper connection on the dAck! (JP1) just waiting to be used for such a purpose.
Here's my reverse engineered schematic of the dAck! input circuit with potential optical input addition:
A couple questions:
Differential vs. single ended input
The CS8414 datasheet shows that one end of the S/PDIF input should be connected to ground [Figure 23]. The dAck! S/PDIF input has the polarity reversed from what I expected, and is differential (sorta AES configuration but 75 ohm); it does work as wired, so polarity must not matter. This seems a little odd to me given that the biphase-mark violations required in the sub-frame preamble are specified with polarity [Cirrus Application Note 22]. Does the CS8414 correct for this? I didn't see anything saying that it does, but it seems that it must.
I'm a bit concerned about the missing 10 uF cap to ground on RXN using the TTL input from the Toslink receiver [CS8414 Figure 24]. Shouldn't matter as far as I can tell, but I'd like a second opinion, is this something I should worry about?
Miniature 5 V regulator
With the assumption that the circuit works as show in the above schematic, what would be a good miniature 5 V regulator to use to power the Toslink receiver? A 7805 is cheap, but I'd like to find something in a more compact package, surface mount is fine (assuming it's not too fine a pitch, don't think that will be a problem for a V reg), 50 mA is more than sufficient. I plan to tap off the dAck! +12 V (nominial) battery.
P.S. for simplicity, I'm ignoring multiple input switching concerns.
Here's my reverse engineered schematic of the dAck! input circuit with potential optical input addition:
A couple questions:
Differential vs. single ended input
The CS8414 datasheet shows that one end of the S/PDIF input should be connected to ground [Figure 23]. The dAck! S/PDIF input has the polarity reversed from what I expected, and is differential (sorta AES configuration but 75 ohm); it does work as wired, so polarity must not matter. This seems a little odd to me given that the biphase-mark violations required in the sub-frame preamble are specified with polarity [Cirrus Application Note 22]. Does the CS8414 correct for this? I didn't see anything saying that it does, but it seems that it must.
I'm a bit concerned about the missing 10 uF cap to ground on RXN using the TTL input from the Toslink receiver [CS8414 Figure 24]. Shouldn't matter as far as I can tell, but I'd like a second opinion, is this something I should worry about?
Miniature 5 V regulator
With the assumption that the circuit works as show in the above schematic, what would be a good miniature 5 V regulator to use to power the Toslink receiver? A 7805 is cheap, but I'd like to find something in a more compact package, surface mount is fine (assuming it's not too fine a pitch, don't think that will be a problem for a V reg), 50 mA is more than sufficient. I plan to tap off the dAck! +12 V (nominial) battery.
P.S. for simplicity, I'm ignoring multiple input switching concerns.
you're right, I've fixed the schematic.
