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My question is essentially the same as this one, except my signal flow is in the opposite direction: Connecting an optical transmitter to a S/PDIF coaxial output

I'm not sure of the optical transmitter's part number because I am reusing one from an old satellite TV set-top-box. I know this makes it hard to give an accurate answer, but I'm not worried about what happens to the gear I'm using in the event of a catastrophe. Anyone's best guess is better than mine, and I don't mind gambling!

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Check inside the CD player, follow the SPDIF output trace and probe around. Most likely you will find the SPDIF output comes from the big CD decoding chip, it will probably be 3.3V in level, and go through a 75R resistor and maybe a capacitor and some other resistors.

Find the point before the resistors and caps where you have a nice logic level waveform, this is what your TOSLINK transmitter wants as an input.

Check if your TOSLINK transmitter uses 5V or 3V3 (for example measure its power supply on the board you took it from).

If voltages are compatible, you can install the TOSLINK transmitter inside the CDP (drill the back side to make a hole) with a bit of perfboard on which you'll put the decoupling caps, maybe a voltage regulator to supply it. Connect its input to the SPDIF signal with a short wire which should be taped against the PCB ground plane, it's a bit "ghetto" but signal integrity should be decent.

bobflux
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For opposite direction can be used same IC, HCU04, something like this... http://www.taligentx.com/projects/opticalconverter/

josip
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  • Much appreciated! The schematic in the project you linked to was so familiar, I knew just [where](http://www.epanorama.net/documents/audio/spdif.html) I'd seen it. Studying it again more closely, I realized it WAS in the direction I needed after all. I had "coax digital output" stuck in my head, so seeing "S/PDIF coax input circuit", along with being a "typewriter" schematic –  Oct 18 '17 at 02:36
  • totally threw me. There are only some minor differences. When I build it, I'm planning on taking +5V off the circuit board rather than build the power supply in the project, unless you think that would be a big mistake? –  Oct 18 '17 at 02:46