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Underwater data collection


#1

hi all. I’m thinking of starting a new project. as a diver I’m joining project baseline which monitors the health of lakes (ph, temperature, nitrate level,…).

what I would like to build is a data logger which tracks temperature, ph and if possible oxygen and nitrate levels in the water.
The finished gizmo would be installed under water at about 5m (so everything but the sensors need to be in a waterproof box).

that was the “easy” part, the difficult part I imagine will be retrieving the data. In an ideal world the gizmo would stream (or send at regular intervals) it’s data to a webserver, so I could make a website that shows realtime data.

I would however be fine with any method of retrieving the data that doesn’t include taking the entire thing out of the water. possibilities I’m considering:

  • RFID / NFC so I could take one of those cards with me and hold it up to the gizmo to download the data to the card (if that’s even possible).
  • wireless network: would this work through water? and how far?
  • some sort of SMS module to send the data via text messages (again does that work under water?)
  • any other wireless technology

basically I’m a novice. I bought a fez spider kit last year and I’m looking for a more serious project to make use of it :slight_smile:

any help/ideas you guys could provide about the possible sensors, modules and power supply would be apreciated.

oh and if this seems like overreaching my other idea would be an underwater GPS so I can track my movements :wink:


#2

This sounds like a very interesting project, keep us informed about it’s progress!

This is not possible. Standard RFID cards are non-programmable. They simply have a trace of wire laid out in a specific pattern to alter an electromagnetic field, giving the checksum.

This is not something we have tested, however I do not expect this to be an easy task. I have not read it fully, but here is a related article discussing what you propose. Maybe they can give you some ideas: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355409/

If the above method is too complex, I would simply setup a time when the device would surface to distribute the data. This way, you would not have to worry as much about how the water density will effect transmission.

From our experience, the GPS module would not be a good fit for this project. I can not get a lock on my phone when I am in a building. I can only imagine putting it underwater.

Good luck, and remember to take pictures along the way!


#3

You probably already know you should start with two things beyond the easy ones (power and waterproofing). Not knowing anything about the real-world use of the sensors (especially underwater), my out-of-the-box comments:

can you float a unit, tethered to your underwater module, that floats on the surface?
for communications, wireless, bluetooth, nfc, ant, ir (probably won’t work at all) are all EMF, I’d look at the whole spectrum to see what is available and has the best transmission through water (i.e look beyond normal radio wavelengths, for example: readily available, relatively cheap laser diodes (see also: http://en.wikipedia.org/wiki/List_of_laser_types#Solid-state_lasers )
there’s the tried and true method - acoustic , lots of piezo electric and other emitters out there.

For many of the transmission schemes, the emitter/sensor pair may be cheap and easy, but you may have to find a good, noise resistant encoding. Another consideration with your communication method to remember is power consumption.

GPS, given you’ve got clear skyview, the issue is signal transparency by water. I know from personal experience (I used to swim with gps attached to track distance) it worked fine submerged up to at least 50 cm).

On the receptor side, don’t limit yourself to size or power – since you only deploy this periodically, you can probably manage bigger sized collectors.


#4

Oh yeah,

search our forums. I’m pretty sure other members of the community have discussed underwater units.

While your at it try codeshare

Google (or Bing, or…) for keywords and always include NETMF as one of the words, Google does a good job with NETMF based searches.


#5

Finally (I’ve got to get back to my regular work :wink: ) If you’re okay with a detachment, find a way to make an attachable data storage unit. Also, if you’re up for the dive, the transmission problem with your broadcast unit will be less of a problem the closer you get.


#6

Hi Ruben. You can also look into underwater acoustic modems to see if they may be a good fit.

http://www.benthos.com/index.php/product_dashboard/acoustic_modems


#7

As this device would be attached to a line that hangs on a buoy how about using two waterproof boxes?

One box could be underwater with the fez spider and all the sensors and one connected with a network cable, attached to the buoy.
then in the second box I could use just about any wireless tech to radiate the data right?

however that would require a second mainboard in the box on the surface.
What would be the best (read cheapest) choice for that? a Cerberus with a (wired) network module for the cable and a wireless network module to transmit data?

or would it be better to use something like a really long usb cable and a wired to wireless network adapter (if that even works with netmf).

or am I over complicating things here?
would it just be possible to extend the sensor wires to about 5m. the DS18B20 temperature probe comes with a 90cm cable. would it require a lot of extra power to do this?

Thanks for the helpfull comments so far!


#8

As I was checking out the different wireless modules I wandered… what’s the range on these things?
The Wifi RN171 Module sounds perfect (though pricey if it would get wet) for what I need, but how close would I need to be to be able to connect? I mean if the device sits on a buoy in the middle of the lake I want to connect to it from the shore, not row to it in a boat :smiley:

I guess I could ask the same for the radio and Bluetooth modules.
Which of these would you guys recommend? as I will be sending simple data I don’t really need anything fancy (except range).


#9

RF doesn’t propagate through water. 2.4GHz(WiFi Bluetooth etc) is especially bad and is why it’s chosen for microwave ovens. Don’t trust the example of the GPS working to 50cm. It won’t stay locked for long like that and it will never acquire a signal. Trust me, I know about GPS. If it must be wireless then acoustic is the only way, but this will be expensive.

Best bet is to use a data cable.

Waterproofing is a big project in itself. Depending on depth you have to worry about the crush pressure. Look for IP68 enclosures to give yourself the best chance.

Let us know how you get on.


#10

For RF comms I would use FreeWave radios such as:

https://www.freewave.com/Portals/0/Documents/Data%20Sheets/GX/LDS0001GLT%20Rev%20A%20GXM-LT.pdf

They are pricey at several hundred dollars a pop, but I would choose these if reliability and range are your primary concern. You’re looking at several miles of range with line-of-sight.

The model above is the TTL version, which makes interfacing to your FEZ much easier. They also have RS232-level interfaces if your device operates at those voltages.


#11

Perhaps you could have the entire module underwater and program it to use a relay to send morse code?


#12

@ Iggmoe - thanks for the suggestion, but that is a bit pricey :wink:
The range doesn’t have to be that far definetly less than a mile. I would estimate max 2 or 300 meters (that’s about 1/3 of a mile I think).


#13

@ Ruben - In that case, you can also look at Parani point-to-point Bluetooth radios, which have an RS232 interface. They’re about $99 each.

http://www.sena.com/products/industrial_bluetooth/sd1000.php

From our tests over water, if the shore and buoy both have omnidirectional antennas (5 dBi) you’re looking at around 150 meters of range. If the buoy has a high-gain omni antenna (8.5 dBi) and the shore has a directional patch antenna (9 dBi), the max range is 600 meters.

The buoy antenna in this case was about 1 foot above the waterline. Higher is better to avoid Fresnel zone effects, so if you can get the antenna higher, you might get even more range.


#14

How about dolphins?


#15

Pressure will be about 0.5 bar at 5m water depth plus the surface pressure so your box will see about 1.5 bar. IP68 is not rated for this depth of submersion. The ideal shape is round and the smaller the diameter the better. The end will most likely be flat so they have to be very much thicker than the cylinder wall thickness. I’ve designed a cylindrical pressure sensor to go in an oil well at up to 7500 psi external pressure and it was 37mm diameter with 4mm wall thickness. The ends were 15mm. That was with 316L stainless. Different materials require different dimensions due to their different yields.

For your depth a length of small diameter thick walled plastic pipe should have enough strength but you’ll need to get ends made for it with o-ring grooves to seal it. Sealing your cable is the tricky part. Ideal if moulded into the end in the same way water depth sensors are usually manufactured. For oil Wells we use 1/4" steel tubing with cable inside but it’s expensive and not easy to work with for such a short length. :slight_smile:

If you can take care of the pressure issue then a 2 part system with a solar powered surface unit on the buoy would allow you to use radio to transmit the data, assuming you have a receiver shore side to talk to it? Zigbee works very well and the pro models will easily cover your range. I think Justin’s RF pipe might also work but I don’t know what it’s range is.

For sensors make sure they are rated for the depth for the sensing part.

It’s a cool project and I wish you luck with it and keep us posted with updates and especially pictures. We love techy porn. :slight_smile:


#16

@ Reinhard - Dolphin = biological acoustic modem.


#17

IP68 is immersion beyond 1m. Generally tested to 3m. This is the highest IP rating you will get for commodity enclosures. Mostly anthing specifically rated beyond that will be very expensive(as it’s expensive to test stuff at deeper depths). Deltron make a number of IP68 enclosures that I think they say are tested to 20m. They are availiable through RS/Allied and Farnell/El14.

Dave is absolutely right about a cyclinder being the best shape to withstand pressure (except sphere).


#18

thanks for the replies all.
I’m not really worried about the waterproof case. yes I could make one from pvc pipe, but there are a lot of (small) boxes for divers that go to 100ft.
for instance this one: http://www.leisurepro.com/p-s3t25/s3-t2500-watertight-case


#19

I thought more about a printer that writes a QR code onto the dolphins skin (no needle printers please).
The trained Dolphin swims to the shore then, where a camera reads the QR. After about an hour the color gets washed off by the water.

p.s. In case anyone does not recognize it: I’m just kidding 8)


#20

The IP68 issue depends on the enclosure type and what the manufacturer claims. Yes, it can be submerged to 1m and not leak but some only claim this for a limited time, not permanent immersion.

The box Ruben links to would be ideal as it will save getting something custom made.