I'm still considering various communication options for the ROV. Here are my current thoughts:
- WiFi over co-ax: The only communications built onto the Pi Zero are WiFi and USB. Running USB over 100 ft of cable isn't practical (optical maybe, but that's expensive), so I've been looking at coxing the WiFi single off the Pi and into some 50 ohm cabling. However, there's no balanced connector on the board and while I did try this mod (https://hackaday.com/2017/03/07/adding-an-external-antenna-to-the-raspberry-pi-zero-w/) to add one, the result wouldn't propagate efficiently. I've also tried using an external USB WiFi adapter with a RP-SMC connector, but this was similarly unsuccessful; again probably because the signal isn't balanced. Unfortunately WiFi signaling is way, way, way outside my area of expertise but I still find the approach appealing.
- Ethernet: Next we have Ethernet. Obviously there's no ethernet on the Pi board so one must be added. The most compact option I've found is to use this board https://www.tindie.com/products/marcel/raspberry-pi-zero-ethernet-rj45-and-usb-hub-shield. Ethernet then opens up some sub-options:
- Cat5: Traditional ethernet is an easy option at this point. 100ft of ethernet is a little bulky. But it's simple.
- Cat3: Taking a step back in time, Cat3 cable should be good enough to run 10Mbits which is enough for control and video (we're not talking 4K here!) The cable is significantly less bulky.
- Powerline: Powerline offers the speeds of 200Mbits with even less cable bulk at only two wires. However it requires an extra adapter (found here https://www.bluerobotics.com/store/electronics/fathom-x-tether-interface-board/ and here https://www.aliexpress.com/item/WisPLC-development-board-Power-line-twisted-pair-Ethernet-interface-200M-Transmission-rate-transmission-of-IPTV-HDTV/32791324046.html) which plugs into the ethernet. It's a little annoying that the only purpose of the ethernet jacks are to plug these two together, and perhaps someone might create a board which does away with these parts.
- USB over ...?: I mentioned USB as not being practical, but if there is a way to run it over 100ft of inexpensive cabling I'd love to know.
My previous ROV has taken the Powerline approach, but before simply taking this route I want to explore all the options. I'd be interested in any feedback.