Serial communication

Control Boards, Controllers, Tethers, Ect.
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mkrkth
Posts: 2
Joined: Mar 25th, 2014, 1:30 pm

Serial communication

Post by mkrkth »

Hi everyone, first time poster here and a newbie at wiring and communication as well so bear with me.

I am part of a project group tasked with developing a ROV within this year and currently I am investigating solutions for the tether. The current idea is to use half duplex RS485 serial communication between one arduino at the top side and one on the ROV. The motives for this is that it reduces the number of conductors needed to 3, Tx-Rx, and common gnd. As we Will equip the ROV with batteries no power transmission is required.

We have been offered a RGB coax cable of this length and I wonder if you guys think this will work well, or should we consider something else?

If you need more background or are just interested in the project I can share more info.

Thanks
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TigerShark
Posts: 108
Joined: Jan 7th, 2014, 2:43 pm
Location: Washington State

Re: Serial communication

Post by TigerShark »

You will need to use twisted pair conductors I believe for RS-485 to work.
kenl
Posts: 153
Joined: Oct 19th, 2013, 8:50 am
Location: South Western Australia

Re: Serial communication

Post by kenl »

Interesting question, from what I gather RGB coax is a bundle of 3 mini coax cables, correct?

I'm sure it would work to some extent, what length of tether? Would you use the third coax for video?
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: Serial communication

Post by rossrov »

Welcome mkrkth. As TigerShark says, RS-485 is suited to twisted pair. As Ken says, would work to a degree. Anyway, I'm guessing that you have 3 coax cables inside an outer jacket. Depending how long a tether you intend on having, you may be able to send "logic level RS 232" straight out of the Arduino TX pin and into The RX pin on the other end and vice-versa. One coax for downlink, one for uplink and the third for video.This will give full duplex and will be slightly simpler than RS 485 on the code side of things. You don't need a high baud rate for control and a compass etc and lower the better with the coax. Not conventional to do this so you will have to try this out, and also the test the video over the particular cable type and length you have. Yes, post some more details of your project - the forum has gone very quiet lately!!
mkrkth
Posts: 2
Joined: Mar 25th, 2014, 1:30 pm

Re: Serial communication

Post by mkrkth »

Thank you for the answers! Yes, the RGB is a bundle of three coax cables. The tether is required to be ~105 m long (I must have accidently removed this from the opening post). We were not initially planning to use the uplink but like to keep the option. Using the third coax for video, through ethernet over coax and an IP camera seems to be a good option.
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: Serial communication

Post by rossrov »

If you are going with an IP camera, then why not ditch the cable you have and just buy 100 metres of RG6 or maybe RG59 and send your video and control data over the same cable? The RG6 will be thinner than than the 3-coax bundle, meaning less drag in the water, and have much better distance capability, being designed for higher frequencies such as needed for IP. The cables inside the 3 coax bundle will have much more loss than rg6. Also, only one Arduino is needed, as the computer can do all the topside stuff.

As you have probably already discovered, there are many different converters available, so you need to do a bit of research if going this way. For hobby ROVs, I see Ethernet over coax as potentially the next best thing to fibre optic - maybe better in that it is more forgiving and the connectors are much easier to fit.
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