Consulting project: Serial communication over optical (SPDIF) interface

[AlexI]

I'm looking for someone to prototype fast, reliable serial communication over fiber optical cable using standard SPDIF transmitter/receiver.  This project would include both hardware (can be breadboard or some simple PCBs) and firmware.  The setup would look like this:

STM32 MCU -> SPDIF transmitter -> fiber optic cable -> SPDIF receiver -> STM32 MCU -> USB HS -> PC running linux

The SPDIF transmitter and receiver can be any readily available parts, for example Everlight PLT237/PLR237.  I'd like to push the data rate right up to the max spec of the parts (25Mbps).  Because of that, the receiving side probably has to communicate with the PC using USB HS, just USB FS is not fast enough.  The microcontrollers can be any STM32 which is fast enough, but it really helps if they have builtin USB HS PHY, for example STM32F730 or F723.

Compatibility with the standard SPDIF (audio) data format is not required, this just uses SPDIF as a data pipe for arbitrary data.  The sending MCU needs to encode data using some type of DC-balanced and run-length-limited line code (Manchester, 8b/10b etc), not necessarily the same one as normally used in SPDIF (biphase mark code).  The receiving MCU needs to recover the clock (it can either use a UART peripheral for that, or something else) and then decode the line code.

The sending side can send a test pattern from memory. Eventually I'd like to be able to use this as an optical UART replacement at 25 Mbps.

If this goes well, there may be a followup project to do the same thing using faster optical transceivers at 100Mbps+.

This is a paid consulting project; you can be located anywhere.  I'll cover expenses (parts, dev kits, custom boards, etc).  Deliverables: working prototype, code, schematics.

If this sounds like something you're interested in, please PM me.

[rhodges]

Have you considered multimode fiber optic modules? When I was working with ATM, these were all over my OC3 (155mb/s) modules and it was super easy to plug in the SC ("stick and click") fiber connectors.
I have sent most of my gear to the recyclers but I might have some I could send you to play with.

[AlexI]

Have you considered multimode fiber optic modules? When I was working with ATM, these were all over my OC3 (155mb/s) modules and it was super easy to plug in the SC ("stick and click") fiber connectors.
I have sent most of my gear to the recyclers but I might have some I could send you to play with.

Thanks!  For multimode fiber optic modules, you mean something like SFP modules just for OC3 not ethernet?  Yeah, I've looked at a bunch of spec sheets recently, for 100Mbit ethernet transceivers as well as gigabit, both SFP and "1x9" form factor, all different types (650/850/1330nm etc).  I haven't measured any of them hands on, but from the specs it seems the modules with builtin drive circuitry pretty much all have a 100-150mA or higher current draw which (I think) is continuous, not just when transferring data.  A proper ethernet implementation would add ~50mA to that for the MAC+PHY (ouch)

I'm guessing it's possible to not use a PHY and just send data to the module, as long as the rate is fairly high (how high?) and it's DC-balanced; basically using the SFP the way I wanted to use SPDIF. The real trick would be using a SFP module at a low average data rate but a high instantaneous data rate, to make the power scale with data rate.  How fast can a module be powered up and down?  After it's powered up, probably the first thing to do is send a string of alternating 1s and 0s to get the AGC on the receiver working... also how long a string?  That's an interesting notion, just seems a bit complicated

[voltsandjolts]

If this is for a low volume application you could consider commercial off-the-shelf USB extenders, optical isolated versions if you prefer. Then the chain would simplify to

STM32 with USB device I/F > USB extender > PC

https://www.lindy.co.uk/usb-c4/usb-extension-c222

[dirkdokter]

Hi Alex,

I can help with this. Can you please send me an email, to the e-mail address in my profile?

Kind regards,
Dirk

[Ice-Tea]

You haven't mentioned range... Rather important.