Maximum devices count in BLE

[Fabien Comte]

Hello,

I have a request for a system (powered with a nRF52840) that should manages up to 60 devices.

Is that possible ?

What kind of settings can I expect (connection interval, …) ?

Thank you

[awneil]

What, exactly, do you mean by, "manage" ?

The SoftDevice Specification tells you that it can support up to 20 simultaneous BLE connections.

Could you use a mesh ... ?

[Fabien Comte]

Thank you for your help.

If I manage both sides of the link, is there any way to do 60 slow connections (ok in this case to be out of specs) or softdevice will kick me ?

About mesh it s not possible for this application.

[awneil]

I think the softdevice will only allow 20.

But you should be able to come up with some sort of "time sharing" scheme ... ?

[ovrebekk]

Correct Andrew. 

There is no spec limitation preventing you from connecting to 60 devices, but we don't have any SoftDevices that can do more than 20 links simultaneously. 

Either you have to connect to 20 devices at a time, and keep the remaining 40 devices in advertise mode waiting to get a connection, or you would need to put 3 Nordic devices on the central side and let them handle 20 connections each ;)

Can you share some more information on what kind of data latency and throughput you need for each node?

Best regards
Torbjørn

[awneil]

ovrebekk said:

Can you share some more information on what kind of data latency and throughput you need for each node?

+1

Fabien Comte: and why a Mesh is "not possible" ?

Also, as you say you're managing both ends of the link, does it have to be BLE ... ?

[Fabien Comte]

Ok I understand, thank you for the answers.

[Fabien Comte]

Mesh is not possible in my case because it's a soft real time system (should react in 500 ms 95 % of the time) with batteries so a connection with a timeslot is much more efficient compared to advertising. And connected way use a radio frequency hopping pattern and minimise collisions that interest me for industrial environnements.

[ovrebekk]

"Also, as you say you're managing both ends of the link, does it have to be BLE ... ?"

This is a good point. If you do something proprietary you can establish a link to 60 nodes or more, but you would have to implement something similar to the Bluetooth link layer on your own, which means the software development effort would be much higher (not to mention the testing requirements...).