Let's say you want to transmit some "non-standard" digital signals over fiber; for example:

• old school parallel I/O
• rotary incremental or absolute encoder from a motor
• digital signals from sensors
• RS232 with archaic DSR/DTR and RTS/CTS requirements
• some obscure industrial fieldbus that they don't make a fiber converter for
• PWM signal to a servo
• just whatever the heck your little heart desires

Do they make a thing for that? I'm picturing a "cheap" (-ish?) transmitter/receiver pair with a wide input voltage range (maybe 1-30V?) and a reasonable frequency response (good for 0 to a few hundred kHz maybe?). No encoding, no multiplexing, no routing, no handshaking or protocol negotiation or anything of the sort; just: digital input->laser->fiber->phototransistor->digital output. One fiber, one transmitter, and one receiver per one signal. Made from real fiber optic components or at least capable the same performance. Is that too much to ask?

Where can I find such a thing? The closest things I've found are some ultra expensive niche I/O-to-fiber converters (like this and this) and ultra half-ass devices (like this and this) which use LEDs instead of lasers and some kind of 2.2mm translucent weedeater string instead of fiber, and are only capable of 50-75m. If these were made with real fiber components and capable of 100x* the distance like they should be, they would be almost exactly what I'm looking for. * (ok maybe I don't need 100x, but 10x would meet all the needs I've had to date)

(Part B) - There are these fiber media converters made for serial (RS232/RS485/422). Do you think this is just simple digital conversion happening inside? Or is there something more? Could something like this be used to transmit non-serial-data signals? I have doubts because I've tried using serial-over-ethernet devices to do this sort of thing and it didn't work.

 

The short answer is most likely no.

Your length requirement limits what you can get for the cheap.
https://www.mouser.com/Search/Refin...r+Optic+Transmitters,+Receivers,+Transceivers

I've used Versatile Link transceivers on boards for all sorts of fiber links under 50M.
https://www.mouser.com/datasheet/2/678/AV02-1501EN_DS_HFBR-0500Z_2020-03-12-1827987.pdf

 

ComFront do TTL/TTL to 4000 feet (1200m) but a lot will depend on the signals youre trying to transmit. Even with the best fibre you need to pre- and post-process the signal to avoid phase shifts and timing distortion. Why don't you give them a ring?

 

Without completely rolling my own, this seems like maybe a workable solution for $46:

It has separate supply terminals for the send and receive, so maybe there are no traces crossing the center of the board and it could be sawn or snapped in half. The SMA connectors could maybe be desoldered and replaced with screw terminals. I would need to make a level shifting circuit for anything other than TTL.

That pair of transmitter and receiver is capable of (used for) 10/100 ethernet so plenty fast, and capable of a over 2km which is more than I need. I'm still open to a more out-of-the-box solution though, if any is known, but I'm prepared to leave well enough alone at this point. I've searched off and on for a few years and this is the most promising thing I've found.

 

Without completely rolling my own, this seems like maybe a workable solution for $46:
View attachment 236954
It has separate supply terminals for the send and receive, so maybe there are no traces crossing the center of the board and it could be sawn or snapped in half. The SMA connectors could maybe be desoldered and replaced with screw terminals. I would need to make a level shifting circuit for anything other than TTL.

That pair of transmitter and receiver is capable of (used for) 10/100 ethernet so plenty fast, and capable of a over 2km which is more than I need. I'm still open to a more out-of-the-box solution though, if any is known, but I'm prepared to leave well enough alone at this point. I've searched off and on for a few years and this is the most promising thing I've found.

Good find, I've used that type of HFBR (different transceivers) board before in a few projects. I did remove the SMA connectors.

 

Good find, I've used that type of HFBR (different transceivers) board before in a few projects. I did remove the SMA connectors.

Nice looking project! What's it do?

 

These devices are for serial touch terminals that use fiber for signal isolation from high energy equipment interfaces.

https://forum.allaboutcircuits.com/threads/video-rebuilding-crts.158801/post-1503410
https://forum.allaboutcircuits.com/threads/secs-ii-host-using-a-pic18f57k42.157503/post-1398263