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Maximum number of BLE slaves with RPi Master

MikeB

I'm working on a project where we have an issue with the current BLE links (non-Nordic, HM-10 devices). Bluetooth Mesh on nRF52s has been identified as the suitable successor, but in the meantime I'm wondering about short-term quick fixes.

The set-up is a Raspberry Pi as a central device, Tx/Rx'ing over BLE v4.1 some information to/from Arduinos, bridged by the HM-10s. The BLE packets are very short, containing either control logic for the Arduinos to drive actuators, or in the other direction are sending basic data from sensors to the RPi.

I.e RPi <-BLE-> HM-10 <-GPIO-> Arduino <-Wires-> Actuators/Sensors

 The instructions/sensor readings are only Tx'd say every minute from each device, so the actual communications requirements are very low.

The issue with the RPi/HM-10 BLE network is that it only supports 5 active devices. Mesh would obviously correct this but our development schedule for it is very long.

- Using any of the nRF52 products, would it be possible to connect, say, 20 devices to the RPi? I think part of the HM-10 limitations come from limited memory, whilst nRF52s have lots of it.

- Does this have much to do with running a BLE v4.x vs BLE v5.x? I.e. does the new Bluetooth v5 specification change things in this regard?

- Do nRF52s running BLE allow for parked slaves? I know this was a feature in classic bluetooth, and since the communications requirements are so low, I am thinking that slaves could go round in order taking turns to be "active".

Much obliged,

Michael

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  • 0 in reply to awneil
    Using any of the nRF52 products, would it be possible to connect, say, 20 devices to the RPi?

     You could attach a 52840 dongle to the Raspberry Pi & run the v6.1 S140 softdevice, along with the multilink example. You could then use the HCI interface to communicate between the dongle & the RPi. You would most likely need to develop some small application on the Rpi to pick up all of the Bluetooth packets from the different sensors/actuators. These two links may also be helpful: link 1, link 2.

    Update: This link might also be helpful.

    I do not believe it is a good idea to somehow try to flash the S132 or S140 softdevice on the Raspberry Pi Bluetooth chip (if that is what you were hinting at, ). 

    Does this have much to do with running a BLE v4.x vs BLE v5.x? I.e. does the new Bluetooth v5 specification change things in this regard?

     Like awneil said, nope. The S132 & S140 softdevices can run 20 links on either v4.2 or v5.

    Do nRF52s running BLE allow for parked slaves? I know this was a feature in classic bluetooth, and since the communications requirements are so low, I am thinking that slaves could go round in order taking turns to be "active".

     You can put a node to sleep & wake it up occasionally, yes. See the documentation here for more info.

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