Using nRF52840 to send data over open sea surface

RE: Using nRF52840 to send data over open sea surface

awneil — Mon, 24 Jun 2019 09:26:28 GMT

[quote userid="80856" url="~/f/nordic-q-a/48826/using-nrf52840-to-send-data-over-open-sea-surface/194161"]I selected it because I am familiar with it [/quote]

"When a hammer is the only tool you have, every problem looks like a nail."

It is better to start with the requirements - and choose something which fits well with those requirements.

Googling "radio communications sea water" finds this (among others):

https://www.researchgate.net/post/Establishing_an_underwater_radio_communication_link

So you really are onto a loser with 2.4GHz !

😮

[quote userid="80856" url="~/f/nordic-q-a/48826/using-nrf52840-to-send-data-over-open-sea-surface/194161"]and because of its range[/quote]

But that only applies in favourable operating conditions.

RE: Using nRF52840 to send data over open sea surface

awneil — Mon, 24 Jun 2019 07:48:26 GMT

[quote userid="26071" url="~/f/nordic-q-a/48826/using-nrf52840-to-send-data-over-open-sea-surface/194226"]maybe a beacon would be more suitable[/quote]

But, as already noted, it'll need fast advertising - which will draw a lot of power.

And, if the device is only above the water briefly, it may not be enough for a scanner to "catch" (beacons are usually assumed to be "permanently" visible)

RE: Using nRF52840 to send data over open sea surface

awneil — Mon, 24 Jun 2019 07:45:34 GMT

[quote userid="80856" url="~/f/nordic-q-a/48826/using-nrf52840-to-send-data-over-open-sea-surface/194161"]Any directives are welcome[/quote]

Still unclear what your goal is - what you're actually trying to achieve - so impossible to give much direction.

But I think the main directive is that BLE is not at all well-suited to this.

Note that the nRF devices can also do other protocols but, because of the water... submersion, anything 2.4GHz is probably not going to be great.

RE: Using nRF52840 to send data over open sea surface

Edvin — Mon, 24 Jun 2019 07:33:12 GMT

[quote user="Harry94"]Well, there are two scenarios based on the range. If the the range can reach the shore then yes, it would be a phone. Otherwise, I could connect to an Arduino enclosed in a buoy in the open sea, and then with an antenna communicate with the phone on the shore.[/quote]

Well. This is all possible, but you would simply have to test in the conditions that the device will operate in to see whether it will be detected or not. As awneil says, maybe a beacon would be more suitable, instead of actually connecting to the device.

RE: Using nRF52840 to send data over open sea surface

Harry94 — Fri, 21 Jun 2019 19:46:43 GMT

I selected it because I am familiar with it and because of its range. I have considered more alternatives, but I am doing a research of what is possible. Any directives are welcome.

-Harry

RE: Using nRF52840 to send data over open sea surface

awneil — Fri, 21 Jun 2019 18:43:34 GMT

Perhaps you need to define what, exactly, you mean by "detect" ?

Remember that we know nothing about what you're trying to achieve here!

http://www.catb.org/esr/faqs/smart-questions.html#goal

If the device is simply broadcasting a "beacon", then you can detect whether that is present or not without having to establish a connection.

[quote userid="26071" url="~/f/nordic-q-a/48826/using-nrf52840-to-send-data-over-open-sea-surface/194087"]This doesn't sound like a case where BLE would be very suitable[/quote]

So why, specifically have you chosen BLE?

Have you considered alternatives?

RE: Using nRF52840 to send data over open sea surface

Harry94 — Fri, 21 Jun 2019 18:37:21 GMT

Edvin

Well, there are two scenarios based on the range. If the the range can reach the shore then yes, it would be a phone. Otherwise, I could connect to an Arduino enclosed in a buoy in the open sea, and then with an antenna communicate with the phone on the shore.

awneil

How could I detect it then? Do you have something more efficient and long range in your mind?

Thank you both for the replies.

-Harry

RE: Using nRF52840 to send data over open sea surface

awneil — Fri, 21 Jun 2019 13:14:29 GMT

[quote userid="80856" url="~/f/nordic-q-a/48826/using-nrf52840-to-send-data-over-open-sea-surface/194093"]What if only wanted to establish the connection (just for detection purposes)? [/quote]

If it's just for detection, why do you need to establish a connection at all?

If it's just for detection, do you need to use Bluetooth at all ... ?

RE: Using nRF52840 to send data over open sea surface

Edvin — Fri, 21 Jun 2019 12:36:08 GMT

On peripheral (typically the device with the smallest battery, so I assume the wristband thing), you need a short advertising interval. On the Central (the scanning device), you need a large scan window (preferably equal to the scan window). Depending on what acts as your central, you may or may not be allowed to use the radio 100% for scanning. If it is a mobile phone, you will not, but if it is another nRF, just set the scan window = scan interval.

Then, on both devices, set your preferred connection interval to be as low as possible. Again, if the central is a phone, you can't decide exactly what it is going to be. If it is an nRF, set both minimum and maximum connection interval to be 7.5ms.

What you would want to do then is to keep track of your connected and disconnected events. That is, the BLE_GAP_EVT_CONNECTED, and BLE_GAP_EVT_DISCONNECTED.

I don't know exactly how the position in the water will affect the range. You would have to do some testing to figure this out.

So what is your central in this connection? Is it a phone, or do you intend to use nRFs as both peripheral and central in the connection?

Best regards,

Edvin

RE: Using nRF52840 to send data over open sea surface

Harry94 — Fri, 21 Jun 2019 12:07:59 GMT

Hi Edvin,

Thanks a lot for your reply.

What if only wanted to establish the connection (just for detection purposes)? What could I use if I wanted to achieve fast connection?

Best regards,

Harry

RE: Using nRF52840 to send data over open sea surface

Edvin — Fri, 21 Jun 2019 11:56:16 GMT

Hello,

This doesn't sound like a case where BLE would be very suitable.

As you say, water is a medium that blocks the BLE radio communication, so it will not be possible to maintain a BLE link under water. In the case that you mention, to transfer data when the wrist is above water, this also sounds difficult, because you need to establish the connection and then send whatever payload data you want to send before the wrist goes back into the water.

To establish a link very quickly, you would need a very short advertising interval and a short connection interval once the link is connected, if you want to transfer data fast. So depending on how long your device is above water, this may or may not work. In normal swimming conditions, I would say that it wouldn't work very well.

The short advertising and connection intervals will also use a lot of power, so your battery life will not be great.

Best regards,

Edvin