VGA, RS232@1Mbps on optical fiber

[DiTBho]

So, I feel the need to move data in a very noisy environment due to high electromagnetic activity.

Fiber optics cables are immune, so that's fine, but since it's a personal experiment, I'm really on a budget(1).

I need to export both VGA@1024x768, and uart@1Mbps, I see there are some products on eBay... anyway...would you trust a metal box that says "OptEcal Fiber" on the top? 

Now I don't want to judge the book by its cover, but if you don't even realize that the serigraphs of the product you sell are wrong...  or you just don't care, and you don't correct them, well... there are probably also hw/sw/fw patches that you don't know/don't care about.

Which usually means troubles for the final user ...

-

Has anyone played with that stuff before, any products with good feedback to suggest?

(1) Say, less than 200 euro for both the transmitter and the receiver, if this makes sense.

[DiTBho]

at most I can build the { RX, TX } modules myself, but I have no experience with the optoelectronic parts.

[berke]

Convert your VGA and UART to Ethernet with a USB capture card and USB to serial adapter using an RPi or something similar, then use an Ethernet media converter to fiber and back.  If you really need VGA and serial output, add an HDMI-to-VGA dongle and another USB-to-serial adapter at the other end.  Parts list:

- Two RPis
- VGA-to-USB capture dongle
- Two serial-to-USB converters
- HDMI-to-VGA dongle

Software:
- For video, probably something based on GStreamer
- For UART, socat might do the trick if you don't need to transmit breaks

[DiTBho]

Universal solution to everything, world peace, food crisis, cancer etc: use an rpi!!!! (sarc)
Sorry, no!

[pcprogrammer]

No experience with but a search on KVM over fiber yields some interesting results.

https://www.rextron.com/Fiber-Extenders.html
https://www.blackbox.co.uk/gb-gb/1439/VGA-KVM-Extenders
https://video.matrox.com/en/products/kvm-extenders

Maybe something can be found in your price range and requirements.

[DiTBho]

to avoid any further misunderstandings:

• must be a pure hw embedded solution
• without involving a GNU/Linux SBC systems or other loopholes of that type

[DiTBho]

No experience with but a search on KVM over fiber yields some interesting results.

Fiber-Extenders
VGA-KVM-Extenders
kvm-extenders

Thanks for the links! Interesting!
That's why I opened this topic: looking for real experiences! Or any suggestions for self-building the modules!
(which I remember, must also carry uart@1Mbps)

[Berni]

Universal solution to everything, world peace, food crisis, cancer etc: use an rpi!!!! (sarc)
Sorry, no!

Well you can still use a x86 PC with a capture card. The beauty of that solution is that it uses all off the shelf consumer things including off the shelf fiberoptic network equipment. So this means devices with a large economy of scale behind them, so cheep to buy.

to avoid any further misunderstandings:

• must be a pure hw embedded solution
• without involving a GNU/Linux SBC systems or other loopholes of that type

What you need is a pretty niche specialized thing, so you will need to pay up the big bucks, or make do with the chinese solutions.

The Chinese tend to be the first place i go to when i need something done cheap. Sure they might not be the highest quality solutions, but i am not usually building a launch control system for a ICBM. I just make sure to test the chinese crap really well to make sure it works for my use case. If it works great, i saved a lot of money, while if it doesn't work just toss it in the bin, it was cheep anyway and go look for a better solution.

The other way is to make your own purpose built hardware solution out of a very fast MCU or a FPGA. However for single one off projects this tends to not be very economical once you consider the number of man hours to complete such a project. So once you factor in the cost of your time, it tends to be cheaper to just bit the bullet and buy the professional solution. Tho for this one the RS232 sounds like it would be easy to do with simply running it trough TOSLINK fiber cables (unless you have a requirement that it all has to go trough 1 single fiber)

[berke]

Universal solution to everything, world peace, food crisis, cancer etc: use an rpi!!!! (sarc)
Sorry, no!

No need to get upset.

https://www.amazon.com/ASHATA-Converter-Conferencing-Conversion-Computers/dp/B081L9KLQ2

https://www.amazon.com/Singlemode-Transmission-Surveillance-Conversion-Transmitter/dp/B088PFXSXJ

Get the 4 channel version, use one channel for VGA, smuggle UART over the other two channels.

EDIT: Actually for UART what I said is stupid, it'll only work in one direction.  But the UART-to-VGA converter is interesting.  Depending on how the VGA-to-COAX-to-VGA device works, it might require microcontrollers for buffering and some analog circuitry for level shifting and generating the sync pulses.

How many fibers can you use?

[berke]

I think your best bet is a VGA-to-IP KVM extender and a pair of bidirectional fiber converters, however you probably need to run some crummy Windows software on the far end to access the remote device.  Unfortunately VGA is rare nowadays, it's easier to find HDMI-to-IP KVMs, and while HDMI-to-VGA converters are cheap the reverse is not true.  So it really depends on the details of what you want to do.

  https://www.startech.com/en-us/audio-video-products/ipusb2vga2

[spostma]

The Startech IPUSB2VGA2 is based on the EliteSilicon EST3868 chip, which is a gigabit Ethernet to 4-port USB 2.1 server,
coupled to a DisplayLink USB graphics card with VGA out.

We have used this combination for years in a medical device that runs the gigabit ethernet over a LC duplex fibre.
The box shown below is in fact an old but fancy desktop extender, and has a 4-port gigabit ethernet switch as well.

It works very well and is stable.  The only problem of this setup is that the EST3868 USB Server driver does not work well with newer Windows 10 updates.
If you work with an older Windows system I can send you a used but functional system; send me a PM if you want one.
It also has two free USB2.1 ports, so you can add an USB-to-serial converter yourself.

[SiliconWizard]

https://www.extron.com/product/foxboxrxvga

[DiTBho]

foxboxrxvga

thanks, it looks *very* interesting 

I will try to contact them in order to understand the cost.
Hope Google will show some feedbacks.

[SiliconWizard]

foxboxrxvga

thanks, it looks *very* interesting 

I will try to contact them in order to understand the cost.
Hope Google will show some feedbacks.

Yes, it has exactly what you need apparently. I'm afraid the cost might be a bit prohibitive though for a personal project, you'll see.

Doing it completely from scratch is of course possible, but not trivial. The tricky part with doing it with off-the-shelf parts will be to mix the serial data with video over a single fiber.
Purely for video, using a VGA-HDMI adapter plus a HDMI over fiber transmitter, such as this: https://www.amazon.com/LornCeng-Extension-Uncompressed-Transmission-Singlemode/dp/B0BN536RN1 , would do for probably much cheaper than my above link.

[DiTBho]

it has exactly what you need apparently. I'm afraid the cost might be a bit prohibitive though for a personal project, you'll see.

Umm, it seems they don't sell to private beings, only to companies.
I will try-again, with local resellers.

Doing it completely from scratch is of course possible, but not trivial.

The biggest problem is to find a bidirectional OptoElectronic module and understanding which is the best data encoding.
That stuff can be handled in HDL, e.g. manchester encoding, vs ... something more specific.

VGA-HDMI adapter

I have done some experiments over the last few years with several VGA-to-HDMI adapters purchased on Amazon, most of them, especialy in the price range 10-20 euro, do not have acceptable video quality and suffer from several problems with colors and thermal stability.

In the end I found only one good VGA-to-HDMI converter, which works well in the long term, do not make the colors faded or distorted, but costs in the range of 40..50 euro.

So, ... I would avoid using it unless absolutely necessary.

The same thing for "VGA capture cards". As easy as it may seem, on a conceptual level, to pair one with a linux SBC, or a little board without an operating system, good luck finding one that has decent video quality, is well documented, and most importantly, comes with opensource drivers that are stable and clear enough to allow you to rewrite it for your final MPU application.

PCI stuff? Forget it!
USB stuff? Yes, it can be paired with modern MPUs with integrated USB, but... well, I have been reverse engineering a VGA-to-USB capture card for 2 years

• costs ~90..100 euro on eBay, second hand
• has very good VGA video quality, up to 1024x768, but only 30fps
• has ZERO documentation, ZERO kernel support
• has MacOS/x86 and Windows/x86 binary drivers only
• has USB2 Full Speed compatibility
• uses 3 different USB methods {bulk, isochronous, ...) to communicate

and this is the best of the various things I've tried, including VGA-USB for 20 euros which only have the good thing about being cheap 

[mariush]

You can get a kvm over ip device for under $100 on eBay, here's a random example with hdmi , dvi-i (includes vga) , usb and audio over ethernet for ~ $75 : https://www.ebay.com/itm/285406835138
Don't know about rs-232 ... maybe there's some rs-232 to ethernet converter cheap, and then you just connect both this one and the kvm over ip to a 2/5/8 ethernet switch and the switch to a $10-20 media converter


example serial to ethernet : https://www.ebay.com/itm/403761948794

[berke]

The biggest problem is to find a bidirectional OptoElectronic module and understanding which is the best data encoding.
That stuff can be handled in HDL, e.g. manchester encoding, vs ... something more specific.

How about using five fibers and doing it the analog way?  Three fibers (R,G,B), one fiber UART TX, one fiber UART RX.  There are transmitter and receiver modules with fast rise/fall times that you probably can use in analog mode.  For UART you could directly use digital transceivers.  You'll probably need some "fast" "video" op-amps for level shifting.  Biggest problem could be TX/RX bandwidth not extending down to DC.  In that case a little bit of modulation might do the trick.  Given that the fiber transceiver bandwidths can be very high, a simple chopper on the TX end and low-pass filtering in the RX end (which can be integrated with the RX amps.)

- VGA input (R,G,B) → level shifting using fast op-amp → chopper → analog optical transmitter → analog optical receiver → low-pass filter → amplifier and level shifter → VGA output (R,G,B)
- RS232 input → RS232 receiver to get logic levels → digital optical transmitter → ...
- RS232 output ← RS232 transmitter ← digital logic receiver ← ...

In the end I found only one good VGA-to-HDMI converter

Care to share?  I'm interested, computer screens don't come with VGA ports anymore.  (And even HDMI is not guaranteed.)

[pcprogrammer]

You can get a kvm over ip device for under $100 on eBay, here's a random example with hdmi , dvi-i (includes vga) , usb and audio over ethernet for ~ $75 : https://www.ebay.com/itm/285406835138
Don't know about rs-232 ... maybe there's some rs-232 to ethernet converter cheap, and then you just connect both this one and the kvm over ip to a 2/5/8 ethernet switch and the switch to a $10-20 media converter


example serial to ethernet : https://www.ebay.com/itm/403761948794

For what I understand from it, is that this is only for transmitting the signal. You also need a receiver for the other end. The opposite goes for the foxboxrxvga solution SiliconWizard mentioned.

So this is also needed. https://www.ebay.com/itm/285406833768?hash=item427392ac68:g:f~sAAOSwuuFkxUSd

Making your own for VGA probably won't be cheap because you need very fast ADC's to capture the higher resolutions. ~125MSa/s for 1920*1080. This also means high speed handling to get it out onto the fiber. But interesting none the less 

[DiTBho]

Care to share?  I'm interested, computer screens don't come with VGA ports anymore.  (And even HDMI is not guaranteed.)

Sure, it's the ‎StarTech VGA2HD2 (link here)
VGA+Audio => HDMI, made in 2012, video up to 1920x1200

Umm, checking on Amazon, it's now listed at ~€170 euro X_______X
Bought in 2022, I'm sure I paid ~50 euro, most likely during a BlackFriday or something.

[pcprogrammer]

The biggest problem is to find a bidirectional OptoElectronic module and understanding which is the best data encoding.
That stuff can be handled in HDL, e.g. manchester encoding, vs ... something more specific.

Maybe this can do, but is gives surprisingly little information about how to hook it up. Guess the "Industry Standard 1×9 footprint package" should shed more light on it.

Edit: This one gives a bit more information.
Edit2: This is also interesting.

[berke]

Purely for video, using a VGA-HDMI adapter plus a HDMI over fiber transmitter, such as this: https://www.amazon.com/LornCeng-Extension-Uncompressed-Transmission-Singlemode/dp/B0BN536RN1 , would do for probably much cheaper than my above link.

There are actually "HDMI fiber cables" that are cheaper than that, I have an 8m one, they sell 30m ones.

Rolling your own is an interesting project but it's not happening under $200 unless analog, and even then...

For starters if you go digital you're looking at a 1.13 Gb/s stream unless you want to compromise on quality.  That will need a mid-level FPGA with gigabit serdes'es to format the streams, maybe an ECP5 can do it.  If you implement 8b10b coding this becomes 1.41 Gb/s not counting overhead.

So count in two dev boards with enough differential I/Os for the ADCs, DACs and the transceivers, maybe $150 a pop?  If they are available, that is.  Pray you don't need any terminating resistors for your differential connections to get the particular kind of signaling the ~1.5 Gbps transceivers want, otherwise you'll have to spin a board.

To digitize the VGA you need a fast ADC or maybe 3 and an analog front-end and the layout can't bee too trash or you'll have disgusting ringing effects around edges.  At the other end you need 3 DACs and also analog front-ends for each channel and the same layout comment applies.  The UART is easy compared to the rest, you'll just slip it in the stream.

I don't even know how much the fiber itself costs.

Cheapest transceiver modules on Mouser start at 15 bucks.  Unless someone finds a full duplex one that'll be 4 modules at $60.  Not counting time obviously.

If you can use multiple fibers and the line isn't too long the analog route seems more feasible to me.

The cheaper transmitter modules use LEDs, those are quoted as having 10ns rise/fall times but that's for full scale, so the bandwidth should be enough for an XGA signal.  With proper readout PIN photodiodes can be pretty fast.  So you have a transconductance amplifier to drive the LED and a transimpedance amplifier at the other end and some level shifting, but it should go down to DC.  I don't even think you need a chopper anymore.  You may have to include some trimmers to adjust the signal levels so that the sync pulses have the proper levels.  You'll have a little bit of skew between channels so the edges may show some slight fuzzy coloring, but if you cut your fibers to within 10 cm this should be minimal.

If you go monochrome you can reduce the video signal to a single fiber.

Duplex on a fiber in analog would require a dichroic beam splitter at each end, you could use RGB cubes used in video projectors and RGB LEDs as a poor man's WDM, you do have two optical tables right?   Or maybe an optical circulator?  Digital you can do TDM.

On second thought, since the return channel is only used for 1 Mbaud UART, maybe a single beam splitter can do it, possibly by adjusting the timing of the UART signal w.r.t. the video signal (transmit during blanking kind of thing), this could be done with a small FGPA or maybe even a µC.

Another avenue could be something that converts VGA to RF, then you RF to fiber and back.

Would be nice if you gave us some more details about the constraints!

[DiTBho]

If you go monochrome you can reduce the video signal to a single fiber.

One of the video screens of the instruments I need to export is green-only, so something that should be { 1024x768, 4bit colors }.
However, for another session I need to export { 1024x768, 24bit colors}, each color has a meaning, so it can't be altered 

[DiTBho]

The serial should be 119200bps (less than the 1Mbps I said above, but) full duplex, as it needs to constantly transmits and receives data 

[Nominal Animal]

Ages ago, I experimented with UART over TOSLINK (i.e. up to 5m of plastic optic cable, 650nm LED), with one cable in each direction.  To keep the duty cycle closer to 50%, I reversed the polarity, so idle == LED unlit.  It worked just fine using TOTX173 transmitters and TORX173 receivers at a couple of Mbaud (I believe I used the Teensy 3.0 I got from the Kickstarter for the test).

The bad thing is, the connectors (TOTX1353(F) and TORX1353(F)) are about 10€ apiece nowadays at Mouser, and not easy to find at reputable sellers; but TME seems to have a small selection of the Cliff versions (OTJ-N and ORJ-N seem quite nice to me) at reasonable prices (~ 3€ apiece).

In comparison, you can get SFP+ transceivers (APSP85B33CDL03 from Mouser) for less than 20€ apiece.  However, you then need a PHY capable of generating the gigahertz signaling from parallel data (like XGMII), a video ADC on one end (like TI TVP7001PZP), and an FPGA to tie them all together; and then design the line code that can synchronize to the various pixel (scan row) video rates with the UART data interspersed, because your bit rate is basically constant.  A lot of work...

The SBC approach does look much simpler and more feasible.

[DiTBho]

The SBC approach does look much simpler and more feasible.

Cannot be used, especially RPIs.

It's a complex question to explain, basically I got a written permission to conduct a couple of personal experiments in the laboratory, but you are not allowed to introduce *anything* that runs an unauthorized operating system. Even the laptop I can take with me to the lab has neither USB stick (1) nor hard drive, it boots from the LAN and can't access anything other than the local infranet. I'm not even allowed to take it out of the lab for the lunch/coffee breaks.

Anyway, supposing you can use a GNU/Linux SBC, well I would use my old friend PowerPC 4xx SBCs.
Why? Because that old guy is my personal "swiss knife" for all the tasks!

The SBC already comes with a built-in uart, and it also has two PCI@33Mhz independent slots (so, there is no PCI bridge between them):

• slot1: you could plug a USB-EHCI, for -say- a VGA-to-USB grabber?
• slot2: you could plug an optical fiber card

so ... job done?
Well, yes and no ...

It's "hypothetically speaking", as you can't bring this technology to the lab, but even if you could, well ... You still have the problem with the VGA capture.

As I said, most of USB-VGA-capture cards (especially cheap ones) are just garbage, HDMI-to-IP-grabbers are even worse, I've hacked a couple... forget them.
There are good Video grabbers out of there but tend to be "binary-only/x86", so ... again, forget them.

I haven't yet finished to reverse engineering the only one decent I found, which is EHCI and can be supported by a custom userspace application with minimal kernel driver needed, just a couple of patches on the USB engine: that's great, as it makes things elegant, quick, and portable, unfortunately the card is very expensive (>100 euro, second hand) and difficult to find on eBay.

Image, to acquire the video-camera, in the end I changed cameras, and I got one that has an HDMI cable set up supported by a special third party converter (+160 euro) that make the camera to be viewed in Linux as if it were a webcam/HD.

Just saying, I would avoid video grabbers like a plague.

(1) just crazy!!!
They desoldered them and filled the holes left by USB connectors on the laptop chassis with melted plastic.
So even if you hide a USB stick in your underwear, you can't physically insert it anywhere ='(