Mesh network to collect large number of proprietary sensors.

[Cássio Miranda Coelho Barbosa]

Hello,

We are currently working on this project that intends to collect the data of various sensors on a large field.

Right now the topology of our system is:
"Low Power Sensors" ---ADV---> "nRF51 Scanner" ---UART---> "GPRS/GSSM gateway"
where we have several scanners and gateways.

We want to make it like:
"Low Power Sensors" ---ADV---> "Friend Nodes"  ---Mesh---> "GPRS/GSSM gateway or Android App"

This way we can collect all sensors readings through the Mesh Network and have only one gateway to upload the readings.


Currently our sensors are programmed to collect RMS vibration data and temperature data every 5sec. and create a package of 8 readings and broadcast it every 40sec. Our package also contains 3 bytes to tell our scanner application the kind of the data, the sensor ID and the version of the package. So the scanner is capable of treating the useful data and upload it accordingly.

In short, we want to make our sensors "inject" 19 bytes of our proprietary data into the Mesh network and upload it to the cloud or an Android App through only one node.

1 - Is it possible? If so, how should we start making this approach?

2 - How many sensors can we use on a single network?

3 - Is it possible to use the smartphone as a real time monitor of the sensors? In this case, the App will only show the incoming data, or it is capable of requesting the sensor states from the network?

We have a semi-truck full of questions but this will keep us entertained for the next days.

Thanks a lot!

[Edvin]

Hello,

How big are the packages (in total) that you send every 40sec? Is it 19 bytes in total? This means that your mesh networks needs approx 3.8bps, which is not much at all, so the good news is that a mesh network should be able to keep up with this (Mesh networks are not known for a great bandwidth). Of course, this depends on the number of sensor nodes you are looking at.

 

1: It depends on the number of nodes that you are looking at using. As I mentioned, a Mesh network is not known for great bandwidth if the number of hops is large. To give a ballpark estimate, in a network with 2 nodes, the throughput can be around 3-6 kbps, while with 23 nodes, the throughput is 0.11kbps. note that these numbers are kbit per second, and not kByte per second. The numbers are also per "sensor node", so with 23 nodes, the gateway will receive 22*0.11kbps = 2.53kbps.
The throughput decreases with the number of nodes, and the number of hops.

2: In theory, you can have 32000 nodes in a mesh network (this number comes from the number of addresses that are available). We have not done tests in this range (I don't think anyone have), but Bluetooth reports tests of a little over 1000 nodes. These tests are, however, typically using an on/off service, like a lighting system.
We have only done tests with 100-200 nodes, due to a limitation in USB ports. The limitation is not in the mesh stack. But then again, this test is using an on/off service, where throughput is negligible.

3: Yes. You will need (at least) one node that speaks both Mesh and BLE. We have released an iOS app, nRF Mesh, which is available on iOS App store, and the source code is also available here. I believe that we are working on an Android version, but I do not have any insight in when this will come.

 

So to sum up, this application depends on how many nodes you are looking at. If the number are around 1000, then I doubt that the throughput will be sufficient. Below you will find a couple of links with some Mesh information. I also suggest that you read through those.

 

https://devzone.nordicsemi.com/b/blog/posts/things-you-should-know-about-bluetooth-mesh

https://www.ericsson.com/en/white-papers/bluetooth-mesh-networking

 

 

Best regards,

Edvin