Tim WilkinsonI'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.
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.
There is always 10Base2 - old 10Mbps over 50 ohms coax.
https://en.wikipedia.org/wiki/10BASE2
Are you sure? yes | no
Oh that takes me back to my college days. I wonder if USB versions of this stuff even exists.
Are you sure? yes | no
There are some old stocks of 10BaseT to 10Base2 bricks. It is an obsoleted standard afterall.
There are 2-pair stranded cat5/cat5e which is all you need for up to100Mbps. They would be more flexible than regular 4-pair ones, but harder to find. Belden has some industrial products.
https://www.belden.com/products/industrial/cable/ethernet/cat5e
Serial over EIA/TIA 422, EIA/TIA 485 if you don't want to work with Ethernet.
Are you sure? yes | no
USB as is I think is limited to 5 meters or so. Last time I look into it was about latency, so it is not a simply way of fixing that with a passive device. You could have a strings of hubs every 5 meters, but that get tedious.
http://www.yourcablestore.com/USB-Cable-Length-Limitations-And-How-To-Break-Them_ep_42-1.html#maxactive
Are you sure? yes | no
Well there is Corning's USB over fiber which will do 100ft ... but it's a bit pricy so I've been ignoring that unless I find a cheaper version. https://www.corning.com/optical-cables-by-corning/worldwide/en/products/usb-optical-cables.html
Are you sure? yes | no
Thinking about this, I have to say it's tempting. I'd need to find some sort of external USB underwater docking enclosure because I don't really want to epoxy a $200+ cable to the ROV.
Are you sure? yes | no
Thanks. I'm going to take a look at the POF stuff. Hadn't heard of that.
The LX200V20 module is the same one I list although the reference I gave includes the extra board to make it easy to plug into ethernet.
Are you sure? yes | no
About the communication, have you considered using pof (plastic optic fiber)?
I was looking into this: http://www.instructables.com/id/Building-POF-home-user-network/
I'm thinking about the possibility of building a small ethernet adapter for the pi zero using this transceiver: https://store.fiberfin.com/index.php/products/active-components/optolock/650-nm-fo-transceiver-125-mbps-industrial-ethernet-with-optolockr-2-2-mm-pof-lvpecl-i-o.html
For the powerline I found also this module: https://aliexpress.com/item/PLC-power-cat-module-RAK-LX200V20-embedded-power-Line-Communication-module-with-ultra-high-speed-200Mbps/32789800405.html
Are you sure? yes | no