mass deployment of sensors

[Luke_123]

Hi,

Just wondering how to configure the BLE for an example use case given below:

A factory where there are 500 temperature sensors installed. What is the right approach/configuration/way to get the data from all these temperature sensors ? How to design a system for this use case, can this be achieved using BLE ?

[Torje]

Hi!

I'm not an experienced BLE developer, but here's my two cents anyway:

You would need several gateways to collect the data from all the nodes, depending on distances/signal strength between them. IIRC, one gateway can usually manage 20 simultaneous connections. So if there were more devices per gateway, you would need to separate them in time (ie max 20 at a time). The complexity of doing this would depend on how often you would need the temperature data. Do you require continuous monitoring, or is it enough to get them a few times per day?

The gateways would be connected to WiFi/LTE/something to send the data to some server. 

If proximity allows it, one node could collect data from several sensors. This would reduce the cost a lot.

There are many factors that would affect the design. I would start with making a drawing of the factory, and plot in all points. This would make it easier to see where you need nodes and gateways.

If all devices reach each other some how, you could daisy chain the data all the way around the factory to a single gateway. That would be a really cool solution, but it would suck if one went offline.

In any case, it should be doable using BLE. It sounds like a great use case for it. It would be easy if you spend a lot on sensors and gateways. It will be more complex the more you try to optimize the design.

There might be some great way in doing something like this that I don't know about. Looking forward to see other suggestions here. In the mean time, I would suggest you share more about the reqs and specs of your project.

Good luck!

- Torje

[Edvin]

I was about to write something, but then I saw Torje already replied something, and I agree with what he says. The answer to your questions depends on a lot of factors, besides the number of temperature sensors. I will add another cent to Torje's reply:

What distances are we looking at? Are all 500 nodes within radio range of a single gateway node? If so, it would be possible to do some sort of beacon sensors, that would just advertise it's temperature data, and the gateway can just scan for advertisements, and forward the data. If they are not within range, you have a few options:

You can use several gateway/scanner nodes, to cover the entire area. Another option is to use Bluetooth Mesh, which is a short range network, where all the nodes will act as relay nodes, extending the range of the network. Whether or not this is possible with 500 nodes depends on the sample rate. Ideally, Bluetooth Mesh is not ideal for a lot of throughput, and since Bluetooth Mesh is a flooding mesh network, every node will repeat all messages it can hear (a very simplified explanation). So this works great for one node reporting to many nodes (e.g. light switch telling all the light bulbs to turn on the light), but it doesn't work as well if all nodes report their own sensor data, like in your case. It heavily depends on the report rate. Also, Mesh nodes draw quite a lot of data, since they have to have the radio turned on in RX mode at all times. 

The same applies for BLE beacons and scanners. How often the devices advertise will set the limit (not a hard limit, but the performance decreases) for how many nodes one scanner can pick up. You can use this tool (online power profiler) to see how much time one advertisement uses on air. Then you have a bit of processing time on the scanner as well. Depending on the advertising interval you can caluclate how many advertising nodes it takes to fill 100% of the time. Then, since they are not synced, you should subtract some, in order to give it some slack. 

Another option is to do this in a BLE connection, but that limits the number of nodes every gateway can handle quite a lot. 

At least, this is something for you to consider as a starting point. Perhaps you can share some more details on your needs, and we can discuss further if you like. Please note that we are closing in on the holiday season, so please expect longer respond times. We will be back to normal capacity in January.

Best regards,

Edvin

[Luke_123]

Thank you Edvin  and Torje  for your replies.