Arduino to Arduino wired communication over 300m+

What is the best way to have 2 arduinos communicate over a 300+ meter wired distance. It must be wired communication. I am creating a underwater rov and am stumped how to do this. Please help! :)

You could try straight serial at a slow baud rate. I have used serial at 9600 over 100m of cat 5 cable. If you switched it down to say 2400, it may well work.

I agree with pluggy that straight serial might work. If you want to be sure, use a "short haul modem" like these on Ebay http://cgi.ebay.com/NIB-Gandalf-Asynchronous-Short-Haul-Modem-RS232c_W0QQitemZ220482631974QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3355c9f926

What would be the speed of that though? I would like to try to make the speed as fast as possible (and cost effective)...since this is how the rov is controlled (this is the remote control and sensor output). I have seen cat5 being used but was unsure how that would work.

RS-422 and RS-485 were designed for just such uses.

If you can spare 4 wires in the umbilical, RS-422 is a bit simpler, because you don't have to worry about keeping both ends from trying to talk at once and making sure they ignore their own transmitted data when it's echoed back through their receivers.

If you do a forum search for RS-485, you should find some examples from people who've gotten the half-duplex thing working.

Ran

I would definitely want to make things simpler and easier...less chance of problems.

Should I use two megas to make this easier?

Mega or mini, it doesn't matter. 2400 baud should be fast enough if you are controlling remotely. For complex communication like video, it may be a different game...

Joachim

Also how can I overlay text over video from the arduino...would that change anything? Also I have seen those networking over power (where you plug in a router to a plug in your house and it creates a network)...can a communication protocol be used that sends communications over the 12 or 24 volt (not sure which to go with yet) wires?

Also how can I overlay text over video from the arduino...would that change anything? Also I have seen those networking over power (where you plug in a router to a plug in your house and it creates a network)...can a communication protocol be used that sends communications over the 12 or 24 volt (not sure which to go with yet) wires?

Also how can I overlay text over video from the arduino...would that change anything? Also I have seen those networking over power (where you plug in a router to a plug in your house and it creates a network)...can a communication protocol be used that sends communications over the 12 or 24 volt (not sure which to go with yet) wires?

Also how can I overlay text over video from the arduino...would that change anything? Also I have seen those networking over power (where you plug in a router to a plug in your house and it creates a network)...can a communication protocol be used that sends communications over the 12 or 24 volt (not sure which to go with yet) wires?

I have seen cat5 being used but was unsure how that would work.

Horribly: Cat5 uses solid wire. It's intended for installations where it's laid down and not moved around a whole lot. The constant flexing, and occasional extreme stressing, that an ROV umbilical goes through would kill it sooner or later (whether it's "sooner" or "later" is a matter of luck).

I know that some professionals have designed telecomm equipment that sends DC up a coax cable to power electronics at the top of the mast. And there are gadgets that do tricks like sending audio from your stereo to your speakers over the AC lines. So making some sort of modem that injects a modulated RF signal into the DC power lines should be feasible. And maybe even cheaper, overall, since you're buying 300m or more of cable: knocking that down from 4 or 6 conductors to 2 could save quite a bit of money.

Ran

Do you or anyone know how to do that?