Controling an arduino at ~150m depth underwater

Hello, the arduino will control multiple dc motors with pwm, and will communicate with some sensors through I2C, there's also camera, I was planning to connect it to a laptop above sea, and power the whole thing through a generator above it (on a boat) and converting to DC below, would a usb with powered extender work? What are my options, I'm quite new to the arduino and what I can/ can't do but I do have the relevant education ( If relevant; circuits, OS, digital logic systems, Computer architecture) .

it's a basically a sub (not a small one) which I need to control and get video live (catching fish), it's a complicated project but I have the time, money, and even manpower, but not the practical experience/knowledge, which is most important part, I was hoping to learn as I go.

Thank you!

If you have a cable connection to the surface it will probably be practical. I imagine the issues of communication would be the same as over a 150m cable on land.

An Arduino has nowhere near the capability to deal with still or video images. And I have no idea how you would transmit video over 150m of cable.

I don't understand why you say "converting to DC below". AFAIK it is easier to transmit DC power over distances.

...R

AFAIK it is easier to transmit DC power over distances

DC transmission is subject to voltage drop and heating effects due to the resistance of the wire. That is why power distribution (mains power) is done using AC at high voltage.

UKHeliBob:
DC transmission is subject to voltage drop and heating effects due to the resistance of the wire. That is why power distribution (mains power) is done using AC at high voltage.

I believe the high voltage is what reduces the heating - by reducing the current.
IIRC long distance Utility transmission systems - such as across the English channel - use DC because the AC just dissipates itself. It may also be (but I am no expert) that AC transmission needs the wide spacing we see in overhead power lines.

…R

AC/DC: AC power transmission is used with transformers, which don't work with DC. Nowadays step-down regulators work with either AC or DC, but more efficient with DC. The power loss in lines is slightly higher with AC than with DC. A transformer can also be used as ballast on the submarine, if required.

HV/LV: The higher the transmitted voltage, the lower the current and consequently the lower the power loss on the line. High voltage requires good insulation of the lines, or wide spacing of uninsulated overhead lines.

One question is about the power source of the above sea station, is it AC or DC, and what voltage? You may need an converter from low to high voltage there, and one or more converters under sea, providing the servo and electronics supply voltages.

I2C is not a good choice for a 150m cable, you're better off with SPI or asynchronous serial transmission, and RS422/485 differential transmission of the signals, or with Ethernet that comes with a protocol for addressing multiple ports.

As already mentioned, the Arduino cannot handle video signals. But I see no need for doing so, your biggest problem will be the signal transmission over the long line. I'd guess that solutions from video surveillance will fit your needs, at moderate video quality.

DrDiettrich: I2C is not a good choice for a 150m cable,

I initially had the same reaction until I realized the I2C communication is local on the sub. (At least that's how I presently understand it.)

DrDiettrich:
One question is about the power source of the above sea station, is it AC or DC, and what voltage? You may need an converter from low to high voltage there, and one or more converters under sea, providing the servo and electronics supply voltages.

I2C is not a good choice for a 150m cable, you’re better off with SPI or asynchronous serial transmission, and RS422/485 differential transmission of the signals, or with Ethernet that comes with a protocol for addressing multiple ports.

As already mentioned, the Arduino cannot handle video signals. But I see no need for doing so, your biggest problem will be the signal transmission over the long line. I’d guess that solutions from video surveillance will fit your needs, at moderate video quality.

It’s a generator that produces AC, I’m not sure what’s the voltage (there’s also more than one) but it’s quite heavy duty, usually used for power tools.

The I2c is between the sensors and the arduino, which are very close (<0.5m), the question is how to control the vehicle, if not through powered usb (https://www.usbgear.com/computer_cable_details.cfm?sku=USBG-2XEXT150&cats=137&catid=137%2C140%2C120%2C199) then how, Ethernet cable? what kind of limitation will hat include? Is there a specific place I can read about “asynchronous serial transmission, and RS422/485 differential transmission of the signal”?

Concerning the video feed, when I think about it, the ardiuno doesn’t have nearly enough ram to handle even on 640*640, what are my option if I need video streaming though (Only way to see what I’m controling), will I need a raspberry on top?

CaptainAhab: Concerning the video feed, when I think about it, the ardiuno doesn't have nearly enough ram to handle even on 640*640, what are my option if I need video streaming though (Only way to see what I'm controling), will I need a raspberry on top?

Use Ethernet, have a hub connection in the sub and stream directly from the camera. Since you have a laptop on surface, I can't see what you'd need a Raspberry for.

Concerning the video feed, when I think about it, the ardiuno doesn’t have nearly enough ram to handle even on 640*640, what are my option if I need video streaming though (Only way to see what I’m controling), will I need a raspberry on top?

Unless the processor is adding some value (like an overlay, or compression), why not just send the video as . . . video?

which are very close (<0.5m)

In the I2C world, half a meter is not close.

+1 for Ethernet cable

What are the limitations when it comes to communicating with the arduino with Ethernet? would it work natively or would I need a switch and a POE splitter?

Assuming the sub has its own batteries for power there is no need for POE. Given the length you need to have glass fiber I guess as CAT5e / Cat6 cables start to have some problems after ~100mtr See also - http://www.techimo.com/forum/networking-and-internet/140605-practical-distance-limit-100mbit-over-cat5e-6-7-a.html

Don't know of a fiber optic solution right away.


Thinking out loud, what might work with 150 mtr is to use (ethernet over) powerline.

Like this - http://www.amazon.com/TP-LINK-TL-PA4010-Powerline-Adapter-500Mbps/dp/B00CUD1M66/

it's a complicated project but I have the time, money, and even manpower, but not the practical experience/knowledge, which is most important part, I was hoping to learn as I go.

An issue with what you say. You said "but not the practical experience/knowledge, which is most important part". Without this, how do you know "I have the time, money, and even manpower," is valid? There are DIY ROV sites and projects on line. You should study what others have done to see how complex the project might be. Just getting a pressure housing that can function at 150m is a challenge. Use the upper right search box and search for ROV to see previous discussions.

AWOL: Unless the processor is adding some value (like an overlay, or compression), why not just send the video as . . . video?

Agreed.

I've read the Raspberry Pi with its camera makes a good "h.264" camera. I couldn't remember the "h.264" term so I went looking for the article I had read. This article has a lot of information about streaming video from a Raspberry Pi camera. The article includes a bunch of links to additional information on the subject.

It looks like Bill (author of the article (and a friend/acquaintance of mine)) started with MJPEG streaming but he didn't like the low frame rate (2fps - 3fps).

Apparently the h.264 protocol allowed him to stream 1280x720 video at 24fps. Bill points out the Raspberry Pi takes about 2 seconds to generate this video so there's significant latency in the video stream.

I'd think a dedicated IP camera should be able to do this sort of compression on the fly.

I imagine the biggest factor determining what sort of connection is needed is the quality of the video one wants to send topside. I'd think you'd go camera shopping first and then decide what sort of cable you need.

Any sort of control commands and telemetry will have miniscule data rates compared with the video stream.

I remember watching a show about ROVs. The guy talking about the ROVs (I think it was James Cameron Now I don't think so.) mentioned when he was down in a full sized submersible, the people with him weren't looking out the sub's windows so see what was going on around them, they were watching the high resolution monitors. He said this is what made him decide to concentrate more resources on ROV subs rather than subs carrying people.

There's got to be information about what sorts of cameras other people use. It sure seems like the decision concerning which camera to use is one of the most important decisions to make with a project like this.

Hi, With water surrounding a cable, does its characteristics change, that will influence its frequency response?

Tom... :)

Robin2: IIRC long distance Utility transmission systems - such as across the English channel - use DC because the AC just dissipates itself. It may also be (but I am no expert) that AC transmission needs the wide spacing we see in overhead power lines.

Yes, that's part of it. The loss is due the insulation material, not the spacing as such.

HVDC links are used when connecting two grids which are either at a different frequency or not synchronized. DC links have much less loss in underground cables due to no dielectric losses. Typically the cost of the converter stations at each end dominate the cost of a short-range DC link. Imagine building two 0.5MV 8GW rectifier/inverters - that's a (large) shed load of thyristors.

The GB and French grids are not synchronized, and the cable is subsea, so DC link was a hard requirement to link them. Wikipedia has lots of useful info.

just wanted to say thanks CaptainAhab, i have searched for days, if not weeks, for a post specifically dealing with ROV's and this type of discussion :) i am in the early stages of a similar project myself, big plans but at least i am trying to research it now (ok, i've had the concept rattling around in my head for 15 years but planning is half the fun, eh?)

i actually bought a 100' length of neutrally buoyant cable from the guys that make the VideoRay so am thinking of a similar system for power/comms etc, albeit i am only planning to make a shallow depth vehicle, 10-15metres maybe they supply DC from the surface, 48 or 74VDC. i will also have an onboard SLA battery there too (helps with ballast and excess power consumption). video i plan to send over the twisted pair of wires with a video balun each end. if i remember correctly, i should get a long distance and minimal interference this way. depending if you chose a passive or active or combination or both (baluns), Max distance can range from 1000-6000feet! also if i can, i'd like to put a basic overlay over the video feed. command signals, not that i have found much in the way of examples online (everybody always tries to push ethernet, i2c, rf link etc) will be initially via RS232 through an RS485 converter (to cope with the distance limitations) from a surface UNO to the vehicle MEGA. much of the transmission theory i remember from a previous job working with cctv, barcode and RF tagging technology so i know these are good options.

http://www.rovfaq.com/index.php?action=artikel&cat=12&id=91&artlang=en shows the tether specs that i can find. the Scout model is good for 75m depth (plus extra tether length) at 48VDCsurface supply, the Pro4 is good for 305metres depth at 74VDC surface supply. i have the cable specs somewhere... but these are still quite thin cables so obviously even steping down the voltage in the vehicle to increase the available current, monitoring power consumption at the vehicle is important.

the problem i have, i'm no programmer so i'm trying to sift through all the individual examples to find bits that i can modify to my own needs. that and a lack of courses or interested others in my area :( at least finding a thread that's on topic is a step in the right direction and gives me hope that what i plan is doable :)

Building for that depth is a challenge. I had a friend that used
schedule 80 PVC but I don’t know the depth he used it at.
Making the port for the camera to look out is a challenge as well as
any inside to outside electrical connections.
Also, because of the index of refraction, width of the field of view
for the camera is reduced a lot, if it use a flat plate.
The wire also need to not have the insulation crushed at 200+ PSI.
One thing I recall, in the connector my friend used, he always filled
the empty places with DC#4 silicone grease. This way there was no
air spaces to get filled with water.
Dwight