2-Wire Tether: Data and Power

To control our submersible we need a way of transferring data from underwater to the surface. We looked into a number of different data transfer techniques and ended up choosing to control our robot over ethernet. After choosing to do this we had a major problem...how are we going to get 200 feet of ethernet cable and still have a light, flexible tether as well as power? And will the power cable effect our data? That much power flowing right next to a data cable can have catastrophic effects. We did some more research on different techniques and decided to use OpenROV's idea of a Two-Wire Tether. They had done a lot of the work for us so this choice was an easy one to make.

The idea behind this tether is that it will provide both power and data in 2-wires. It does this by using Ethernet over Power (EOP) adapters. These adapters were originally made for homes where wi-fi didn't have enough range or you cannot find long enough ethernet cords. You can plug these converters into  2 different outlets on opposite sides of your home. This allows for ethernet speed connection over larger distances and with lest instillation effort. Not surprisingly though this is the best way to transfer data and power below the surface of the water without much interference. A picture of EOP device attached to the Pi is below:

Ethernet Over Power (EOP) attached to a Raspberry Pi
Because we are not using a direct connection to a laptop setting up EOP was very easy. We just wanted to see if it would work. One end is plugged into the Pi and the other into a router. There are ways to attach the Ethernet directly from one computer to another, but as of right now we do not need to do that.

Check out other posts which show how we sent commands back and forth using EOP.

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