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Video and RS485 on single pair


(Dean Rundle) #1

Hi All,

I have a single pair of wires spare available from a subsea unit to surface and need to try and get a RS485 and video signal onto the single pair. I was hoping to use a pair of Fathom S cards to get the two signals presented on the Ethernet plug and then convert Ethernet to a 2 wire signal using a pair of Fathom X boards in between the Fathom S boards. Is this feasible/possible? I appreciate the TTL has to be converted to RS485 and have sourced suitable converters.

In the documentation there is a description to link the Tether X into the Tether S and then use the normal Tether S connection but I don’t have enough wires?

Any advice greatly appreciated.

Cheers

Dean


(Jacob) #2

As far as I know this is not possible. Neither the Fathom S nor the Fathom X are designed to do what you describe.


(Dean Rundle) #3

Thanks Jacob, I had figured this out myself already. I incorrectly assumed that the output of the tether S was an ethernet signal due to it using cat 5 cable.

Sure to be a solution out there somewhere

cheers

Dean


(Joe) #4

Our robotics team tested multiple video feeds over ethernet and the latency made the craft uncontrollable. The frame rate was very good because the bandwidth was more than sufficient, but the video was al;ways about 3 seconds behind due to the low performance video encoders built into the cameras. It didn’t work for control, but could work well for documentation type video.


(Nathan Perry) #5

This is very possible, but sort of difficult with off the shelf products. The BlueROV2 does pretty well sending video and data over a single pair (via ethernet using the FathomX). With some programming ability it should not be difficult to get the Raspberry Pie to simply send video and bi-directional data over Ethernet… I just have not spent the time to try to put that together, maybe someone here has, or could…

I am also looking at ways to get my video and data on one pair instead of 2. I have only seen one type of off the shelf device that seems like it may work, but maybe latency is an issue like @subsearovers mentioned.

Check this HDMI extender out though, it may work if you connect it to a FathomX?? It also has bi-directional RS-232.

https://www.jtechdigital.com/j-tech-digital-proav-hdmi-extender-h-264-encoder-and-decoder-over-ethernet-cat6-extender-matrix-12x12-8x8-switch-switcher-extender-by-single-ethernet-cable-up-to-400ft-receiver-decoder-231.html


(Dean Rundle) #6

Thanks Nathan, will look into it.


(Joe) #7

Our team currently uses a pair of passive coax video over ethernet blauns to send up to four streams over a single CAT5e wire (CAT6 is less flexible) cable and it works fine with low latency, but that’s not ethernet. I misunderstood what you wanted to do. We actually want packetized video when we ran our IP camera experiment that resulted in excessive latency.
We use something like this:
https://www.bhphotovideo.com/c/product/898852-REG/MG_Electronics_MG_43_Passive_UTP_Video.html


(Lawrence) #8

There are also RS-485 over Ethernet devices that would give you that capability. One at each end gives you an RS-485 tunnel.


(Nathan Perry) #9

Update:
I went ahead and bought the “HDMI Extender / H.264 Encoder and Decoder” that I linked to above and did some testing. I had good results with the setup working as it was designed to work (over Cat5 cable), and when the Cat5 was replaced with a connection via the FathomX it continued to work equally as well. This setup gives tou video, stereo audio, and full duplex data up to 115.2k, on a single pair.
The only thing I dislike about video over IP is that there is always latency. In this case there is about 200-400ms delay in the video/audio feed. I have not tested to see if there is a delay in the data stream. One thing to note, the delay is all in the HDMI Extender box. Adding the FathomX did not add any delay.