Using RS485 for communication


#1

While looking around for option for the Ethernet connection, I thought about trying to play with RS485 (serial).

There are FTDI USB adapters (http://www.ftdichip.com/Products/Cables/USBRS485.htm) that we could use. Just lacking a second USB port on the BB.

Or we could use just the chip and wire it up to the USB hub on the BB. But I haven't found out how to do that.

Or we could use the I2C bus interface of BB and use one of the FTDI chips that interface that: http://www.ftdichip.com/Products/ICs.htm

RS485 is specified to a max cable length of 400ft/1200m. Max bandwidth with 4000ft being 100Kb/s but as we wouldn't go for a cable that long it should be considerably faster. Not sure if that would be enough for video. For the cabling required, it would be at minimum single twisted pair (2 wires) with an (according to wikipedia, http://en.wikipedia.org/wiki/RS-485) optional 3rd wire for voltage reference.

To establish the TCP/IP connection, we could have pppd running on the BB and use a dailup connection (as 'in the old time' with modems).

Haven't done anything with RS485 or I2C. But that's a minor concern :)

What do you think?

Cheers

Dominik


#2

Hey Dominik,

Just posted this on the wiki forum...

http://wiki.openrov.com/index.php/Special:WikiForum?thread=11&form=true&editcomment=2&action=purge


#3

Can you elaborate a bit on "(1) Unsafe if done improperly" re Ethernet over powerline (?AKA? POE power over Ethernet) with single UTP?


#4

Sending AC through water is dangerous, and we've always been concerned about incorporating that into a design that we encourage people to build.


#5

Hi David,

Cool, thanks. Once I'm a bit further with my first (standard) ROV I hope to have the chance to start experimenting. For example with the RS485 to see it works bandwidth wise.


#6

That sounds great. The more experimentation the better (as long as it's safe!! ;) ). Keep us informed!!


#7

Have you had any results with this method?

I have always been curious about the feasibility of sending video over 485.