Timbatao
Posts: 1
Joined: Fri Sep 14, 2018 8:36 am

Dive Coms

Fri Sep 14, 2018 8:45 am

Hello,

I am working to the diving company, and we have coms for surface supply diving. They are expensive and breaking down so often like raining in Scotland....
However, I got the idea to make coms with raspberry PI.
Problem is I am not experienced with PI, but however, i know blibs and blobs about Linux and basic electronics.
But i think it is not so much complicated because you need:
2 audio inputs
1 video input
1 mic
We would use existing com box and some features.
Image

Maybe by any chance, anyone would help me to start with this and give me some advice?

mattmiller
Posts: 1954
Joined: Thu Feb 05, 2015 11:25 pm

Re: Dive Coms

Fri Sep 14, 2018 9:34 am

However, I got the idea to make coms with raspberry PI.
A homebrewed Pi setup is almost certainly NOT going to be more reliable than a commercial product

And a Pi isn't a great device to try and do comms with anyway

B.Goode
Posts: 6537
Joined: Mon Sep 01, 2014 4:03 pm
Location: UK

Re: Dive Coms

Fri Sep 14, 2018 9:44 am

give me some advice?
Probably not the 'hacking' advice you hoped for. But...

Check with the Company Director responsible for Health and Safety and maybe your company lawyer before going much further.

I am not a diver or a lawyer, but if I were putting my life in your hands on a dive I would expect you to have robust and reliable systems in place to protect me. Perhaps there are formal regulations that enforce this?

Something put together by some described as "not experienced with PI, but however, i know blibs and blobs about Linux and basic electronics." does not seem to match up to that requirement.

pfletch101
Posts: 210
Joined: Sat Feb 24, 2018 4:09 am

Re: Dive Coms

Fri Sep 14, 2018 3:13 pm

I would endorse the (perhaps discouraging) advice given by others. If equipment used in diving fails, people can quite conceivably die! Quite apart from the liability issue, would you want that on your conscience?

ejolson
Posts: 2008
Joined: Tue Mar 18, 2014 11:47 am

Re: Dive Coms

Fri Sep 14, 2018 6:14 pm

Timbatao wrote:
Fri Sep 14, 2018 8:45 am
Hello,

I am working to the diving company, and we have coms for surface supply diving. They are expensive and breaking down so often like raining in Scotland....
However, I got the idea to make coms with raspberry PI.
Problem is I am not experienced with PI, but however, i know blibs and blobs about Linux and basic electronics.
But i think it is not so much complicated because you need:
2 audio inputs
1 video input
1 mic
We would use existing com box and some features.
Image

Maybe by any chance, anyone would help me to start with this and give me some advice?
I wonder why the existing communications boxes keep breaking.

It appears to be a two channel analogue mixer in a weatherized box with talk back feature. Since the analogue circuitry needed to implement such a device is well understood, perhaps the box isn't as weatherized as it appears. The next time you put one back together, it might be prudent to squirt a little silicone caulk around the seams before tightening down the screws. Do you use batteries with the device? That could be another point of failure.

As you seem to be looking for a Pi project, one could ask what good could a Pi be for a surface supply diving enterprise?

As you may already know, the Pi is a real computer designed for teaching children how to program that has been appropriated by hobbyists to build IoT devices for home use. The resulting reliability of each project varies with the skill of the maker. However, most of the benefits come not from reliability but from flexibility and originality.

Unfortunately, the Pi doesn't have built-in analogue inputs. While the forums are full of people asking for more RAM and faster USB ports in order to duplicate the functionality of a desktop computer, what makes the Pi interesting is that it is not a desktop computer but more of an up in a balloon, around in a robot type of device. In my opinion, an important feature the Pi missing in this regard is built-in analogue to digital converters that could be used as audio inputs, joystick interfaces and for various sensing and control applications. Just like GPIO, having analogue inputs would open doors to many people who don't have the resources to design or purchase add-on hardware for each project and experiment. Making such hardware built-in would also lead to standardisation and focus for the community.

Back on topic, the Pi does have built-in audio outputs, so it would be easy to turn a broken communications box into an internet radio that could be placed in the office or home as a conversation piece. It also has a built-in camera interface with matching camera which could be used to monitor operations at the surface for training and analysis. With a USB microphone and audio input dongle, communications from the audio output of a working analogue communications box could be recorded as well. Making either of these last two ideas reliable will likely be surprisingly difficult.

While audio hardware along with digital mixing software could, in theory, be used to replace the entire communications box, the result would likely have the audio quality of a satellite telephone connection from India to Mexico, whereas, the analogue solution you are currently using introduces almost no latency or lag and should be more reliable.

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Joel_Mckay
Posts: 142
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Contact: Website

Re: Dive Coms

Thu Sep 20, 2018 10:00 am

I have built marine based systems for several years, and a unshielded Pi unfortunately drops an RF spur in the emergency locator safety bands.
You will never pass the ISO EMI lab test with a pi...

If you are playing with underwater acoustics, than I would suggest looking at a classic ultrasonic FM transceiver using an SA605: https://www.nxp.com/docs/en/data-sheet/SA605.pdf

USB sound-cards are common (some have stereo mic inputs), and broadcasting AX.25 over audio channels has been around since the dawn of the internet. Look at the direwolf deb package for details.

There are also air-gap jumping sound-card to sound-card links you can try:
https://github.com/Katee/quietnet

commercial kits are around that will probably end up costing less than developing something that needs to be reliable.

Best of luck,
J
Last edited by Joel_Mckay on Thu Sep 20, 2018 12:59 pm, edited 1 time in total.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 20702
Joined: Sat Jul 30, 2011 7:41 pm

Re: Dive Coms

Thu Sep 20, 2018 12:02 pm

Joel_Mckay wrote:
Thu Sep 20, 2018 10:00 am
I have built marine based systems for several years, and a unshielded Pi unfortunately drops an RF spur in the emergency locator safety bands.
You will never pass the ISO EMI lab test with a pi...
Whilst we do not claim to pass anything but the consumer electronics EMI standards, just out of interest, where was the spike? Also which model Pi did you see it on and did you have anything plugged in to it?

Note to the OP, we do not recommend the Pi be used in any safety critical environment. Safety critical devices are expensive for a reason, much testing and redundancy!
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

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Joel_Mckay
Posts: 142
Joined: Mon Nov 12, 2012 10:22 pm
Contact: Website

Re: Dive Coms

Thu Sep 20, 2018 12:45 pm

jamesh wrote: Whilst we do not claim to pass anything but the consumer electronics EMI standards, just out of interest, where was the spike? Also which model Pi did you see it on and did you have anything plugged in to it?
You can have a look at the most problematic spur yourself (*there are a lot more besides this one), and while your claims are valid for modular FCC pre-compliance... they are meaningless for a widget containing modules that will need certification... The FCC & CE still demands lab certification your device will pass the unintentional emissions tests. Note, the pi B+, Pi2, Pi3, Pi3 rev1, and pi3B+ ...all share a similar set of problems...

We did ultimately solve our specific issues, but it would have been the same project no matter which SOM supplier we chose.
I still build quite a few hobby projects with these, and like the designs consistency even if it has some challenges.

https://www.youtube.com/watch?v=UmzsWxPLIOo

Cheers,
J
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jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 20702
Joined: Sat Jul 30, 2011 7:41 pm

Re: Dive Coms

Thu Sep 20, 2018 1:59 pm

Joel_Mckay wrote:
Thu Sep 20, 2018 12:45 pm
jamesh wrote: Whilst we do not claim to pass anything but the consumer electronics EMI standards, just out of interest, where was the spike? Also which model Pi did you see it on and did you have anything plugged in to it?
You can have a look at the most problematic spur yourself (*there are a lot more besides this one), and while your claims are valid for modular FCC pre-compliance... they are meaningless for a widget containing modules that will need certification... The FCC & CE still demands lab certification your device will pass the unintentional emissions tests. Note, the pi B+, Pi2, Pi3, Pi3 rev1, and pi3B+ ...all share a similar set of problems...

We did ultimately solve our specific issues, but it would have been the same project no matter which SOM supplier we chose.
I still build quite a few hobby projects with these, and like the designs consistency even if it has some challenges.

https://www.youtube.com/watch?v=UmzsWxPLIOo

Cheers,
J
Blimey, those spikes are tiny! I guess the rules are somewhat stricter than for consumer ratings! Thanks for the graph, quite interesting!
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Please direct all questions to the forum, I do not do support via PM.

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Joel_Mckay
Posts: 142
Joined: Mon Nov 12, 2012 10:22 pm
Contact: Website

Re: Dive Coms

Thu Sep 20, 2018 9:02 pm

jamesh wrote:
Thu Sep 20, 2018 1:59 pm
Blimey, those spikes are tiny! I guess the rules are somewhat stricter than for consumer ratings! Thanks for the graph, quite interesting!
Everything looks small standing far away, and depends on the orientation of the object relative to the receivers antenna.
https://en.wikipedia.org/wiki/Inverse-square_law

For example, marine certification IEC60945 safety rules will fail a Pi in several areas, as the standards state a device must be under::

150 kHz – 300 kHz 10 mV/m – 316 μV/m (80 dBμV/m – 52 dBμV/m)
300 kHz – 30 MHz 316 μV/m – 50μV/m (52 dBμV/m – 34 dBμV/m)
30 MHz – 2 GHz 500 μV/m (54 dBμV/m) except in 156 MHz – 165MHz
156 MHz – 165MHz 16 μV/m (24 dBμV/m) quasi-peak or 32 μV/m (30 dBμV/m) peak

Even if we ignore the radar exposure tests, most FCC/CE approved consumer land equipment will fail marine IEC rules.

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