everyone will ask - where to get one, when, how much, design open source?..etc! 
Price depends on volumes, € 25.00 ex. VAT for one-offs, around € 17.50 ex. VAT for smaller amounts (10-100). The design is not open source in the way that we provide gerber files and such to produce your own PCB, but obviously we do provide electrical schematics needed to write software for it. It’s Arduino compatible. 4 programmable I/O-lines have been provided on the outside, and selected in a way that you can create an i2c interface, have an analogue input and we also provide an interrupt input. And of course: it has an LED
Such a thing is necessarily larger than the integrated MCU+Radio modules already on the market, because the RFM95 itself is larger at 16mm x 16mm than something like the Murata at 12.5 x 11.6. Also an ATmega328 is drastically limiting compared to the MCUs in integrated modules and typically means people cut corners and only partially implement LoRaWAN.
But its unclear that any LoRaWAN solution is going to work well for the asker’s underwater application…
@cslorabox I wasn’t claiming it’s top of the line but it fulfills our purposes and it’s cheap. And also important for us: the GND plane is still big enough to use a helical antenna on it and have an acceptable RF performance.
As to underwater use, the formula gives that the theoretic maximum underwater penetration for 868 MHz for salt water is 8 mm, and for fresh water it’s 31 cm. That of course also requires that the geometry of the antenna is adapted to the dielectric constant of salt resp. fresh water.
1 Like
If you put the gateway antenna right over shallow water you might get something, but you won’t get any meaningful range to a gateway at a distance in the usual LoRaWAN manner.
As such, LoRaWAN on conventional frequencies makes no sense for such an application.
If someone wanted to put a local reader over a shelfish bed, they should probably look at something like low frequency RFID schemes or something like that.
@ecosoph reach out to R. Daniel Harris. He’s done similar work with snails and oysters.
http://robertdanielharris.com/research.html
Thank you @salvagione I’ve already sent him a mail. He focuses more on the biology part, which is great.
@bluejedi it is or use with LoRaWAN
@cslorabox I would be happy with a few meter 3-7m under water already, which depends strongly on the water conductivity, as I’ve estimated. It might also be an option to pull the antenna larger to the water surface (sth. like a floating antenna).
I’ve looked for low-frequency alternatives, ther’s a group at the Iowa university that uses 315MHz transmission:
RFID would for sure be the best option but to my knowledge the wire would need to be extremely long and if badly designed the losses there are heavier than for a bad designed 868MHz antenna. Anways, I see the advantage of using 13.56MHz or even lower frequencies with 133kHz that is used in pet tagging.
I’ll be thrilled to hear your feedback 
you seem to have some practical experience.
@rharte that’s cool and extremely small. I would prefer a 64KB RAM ATMEGA processor over the ATMEGA328P but if your whole code its onto it, then it is just great.
Underwater needs are pretty clearly not an application for LoRaWAN or UHF frequencies, but rather for the low MHz to more likely high Kilohertz range.
“Antennas” are more likely to be coils than wires.
@cslorabox yes that is my worry to and as electrical engineer I should know better but I still wanted to test it. The university of Iowa used 315MHz frequency successful for unerwater transmission:
https://ieeexplore.ieee.org/abstract/document/6493575
They use following radio module: linx trm-315-lt, the max output power is only 10mW:
I’ve searched many hours for suitable low-requency radio modules but found nothing. I can think of so many applications or LoRa but as you say underwater might just not be one.
Can you think of suitable radio modules?
Thanks for the valuable input, I agree that there are better options than LoRa for underwater communication but I still think the transmission could be a few meters:
and strongly depends on the conductivity of the water.
You could transform “think” in to “know” in the space of a morning …
Only by buying expensive gear that won’t remotely satisfy the actual need.
This whole thread and contemplation of LoRa is a waste for the asker’s purpose.
I was trying to get it to reach a conclusion with the use of a device, a gateway and a bath tub.
That would require investing in a device and gateway that aren’t useful for the actual goal.
You could do it if you like, it makes absolutely no sense for the asker to waste their money doing so.
(Yes, one could run tests with two nodes and RadioHead… but the greater principle here is applying some common sense to recognizing grossly unsuitable ideas before sinking time and money into them)
@cslorabox thank you! well spoken.
Just for the interested reader, I’d like to share my literature research for underwater lora applications:
-
TTN forum post’: Underwater range of LoRa
-
Transmission tested in the Dishui Lake in Shanghai with relatively high conductivities of 0.24 S/m (transmission maximum was 3m): https://sci-hub.se/10.1109/APMC46564.2019.9038666
-
Blog entry with a formula to estimate the damping under water: https://smartmakers.io/en/lorawan-range-part-2-range-and-coverage-of-lorawan-in-practice/
-
From minute 14:00 on, gateway placed above water 1m @SF12: https://www.youtube.com/watch?reload=9&v=ZK-ttu5xrIE , minute 17:50 it is suggested to equip a fish with a LoRa tracker and just get the signal if it swims on the surface.
-
Internet of fish: http://folk.ntnu.no/alfredse/Forslag%20til%20prosjektoppgaver%20hoesten%202019.htm
So to sum up, there are proof of concepts up to 3m. BUT: I am still unsure what RF communication is suitable then… :).
I know this is a LoRa-forum but eventually you can still recommend me sth.
1 Like
Dear TTN-fellows,
I’ve recently opened a thread about small-sized LoRa modules for under water communication:
I haven’t completely dropped the idea of using VHF and UHF bands to bridge a couple of meters in water but I’d like to emphasize here again that VHF/UHF radio modules and under water communication is not a good match.
Anyways, on my search or lower frequency modules I came across this series from hoperf:
RFM98PW
https://www.hoperf.com/modules/lora/RFM98P.html
The model number RFM98PW-169S2 supports 169MHz at 27dBm.
Has anyone of you experience with these modules and in particular what gateways can be used for those?
Thank you guys!
In theory, most gateway based on SX1302 should support it since it is usually paired with a SX1250 as RF front end which cover the band 150-960 MHz. But the antenna matching is typically targeted for 868/926MHz, so I have no idea what kind of performance you can get with off the shelf gateway …
Are you aware of wize?
Kind regards
VHF isn’t going to make enough of a difference to make this idea workable, and your costs in using atypical hardware will go through the roof.
Please stop chasing dead ends; if you need to get a signal out from under water, you’re in the regime of kilohertz to at most of few megahertz, or more likely not using RF at all. And in any case you’re talking to a very nearby pickup antenna.
If you have some other scheme for getting from the shellfish beds to a box on a pole on the shore, then you could possibly consider LoRa from there, though realistically given all the investment in gear for one small area you might as well just put a mobile data modem in it and not suffer the very extreme limitations on how much data you’d be able to send from a single LoRa device.
What are the rules for using that band in your area ?
That there are node devices available is of little advantage if there is not enough bandwidth available to run a multi-channel gateway.