SPDIF using laser

Attached are the photo's of my test setup.

The AD converter is hooked up to the pre-amp output of my receiver.

The amp is a wondom JAB5 set to slave mode and receives an I2C signal from the SPDIF to I2C converter board (I wanted to skip to repeated A -> D -> A -> D -> A conversions)

The amp is powered by the wondom BCPB6 battery board using 6x 21700 lithium cells

One pic is with the laser hitting the receiving diode head on

The other pics shows the connection using the SPDIF output

I did some more testing;

- on a headphone amp with optical input, also no audio signal from the laser

- optical transmitter has 3 pins. Between 2 of them there's a voltage of 3.25V. Between these 2 pins the laser diode is powered properly. 2 other pins also have a voltage of 3.25V as long as there is no load. With the laser diode connected the light is very dim and the voltage drops significantly. In both cases no audio signal is received however. have the feeling the first 2 pins are the supply voltage, and the other combination forms the signal input. It almost seems like a mosfet is needed to get the laser to be powered by having the 'signal' input switch the mosfet at high frequency whilst providing the supply voltage

I'm no electronics engineer by any means and I'm surprised I didn't fry the AD converter already. I'm at a complete loss though how to get this to work. The video made it seem easy... what's the trick here?!

No pictures. I'll look into the details later when I get a moment (this is Matt's design).

Hm, let me try that again

Haha! Working on the floor - that reminds me of someone I know (cough, cough). Do you, perchance have access to an oscilloscope? It's just easier to see what's going on when you have a visual reference. Don't worry if you don't, we'll have to go the looooong way around. 🙂

Haha, yeah. With the marvels of today's technology there no more 3.5mm output on my phone, so although the rest of the setup is wireless, I'm stuck working with my short rca cables from the ht amp.

Unfortunately no oscilloscope. I did order another AD converter (same as shown in the youtube vid). That'll take a couple of days to get in.

I'm just going though this test setup phase first, making sure I can actually get things to work before I order the speaker drivers etc.

Okie dokes. I'm bit under a rock right now (and I'll have to check back unless you tag me so I won't know if you've replied (you're out of the moderation queue now).

You can get a workable (if not amazing) scope from Ali for under £50 these days. Look for something with a meter and a signal generator as these come in very handy. I do a lot of my work in simulation before I put it on the bench and then there's the iterative designs for the PCBs (have a gander at the USB-C mic thread or my GitHub and you'll see this.

I'll try to figure out what's going on as soon as I've finished the remaining capsule amplifiers (I only have one to do now).

Alright, so with the new analog to spdif converter it worked straight away. Whoever is attempting this; the generic aliexpress ones won't work. I got a linkfor ulk039 off amazon (2-3x the price of the aliexpress stuff), and they seem to be getting hard to find. 

Always happens when someone finds something good and then puts it on the web. 🙁