nrf52840 ble disconnection issue

[EVOV Solutions]

Hi,

I have a medical device where my mother board has a NRF52840 chip which communicates with a Android Tablet through blue-tooth. We find it gets connected with few tablets & not with others. Following problems we see - 1) Getting connected through serial terminal manually & thereafter remains connected, 2) In other cases it connects and disconnects after say 20seconds

Can you suggest some solution for this?

Also, as my device runs on continuous main power, I want to run NR52840 on Class blue tooth...Is it possible to run it on classic blue tooth to maintain connectivity?

[Simonr]

Hi

Are there specific tablet models you're not able to connect to or maybe the device is only able to connect to X amount of tablets before not being able to connect to more? It could be that some of the tablet doesn't support the connection parameters your nRF52840 board provides, or that you reach the maximum number of links is reached in the nRF52840 is reached (this is set in the config fie as the NRF_SDH_BLE_TOTAL_LINK_COUNT and  NRF_SDH_BLE_PERIPHERAL_LINK_COUNT defines. To find out why devices are disconnected, we need to see a disconnect reason of some kind. Do you have logging enabled on the nRF side showing some kind of return or error code when the disconnects occur?

As for your classic Bluetooth question. No, the nRF5x series only supports Bluetooth Low Energy, and are not compatible with Bluetooth Classic devices.

Best regards,

Simon

[EVOV Solutions]

Hi,

We connect only one tablet with one device. It gets connected with SAMSUNG tablet however with others we observe - a) Gets connected through serial terminal on manual intervention, b) It gets connected & then disconnects after ~20seconds., c) We observed the disconnection is with tablets having processor speed less than 2gHz., d) We see connection last from App side

Is it a hardware or firmware issue?, What can be the root cause. What is required to ensure connections last. Whether we need to do change in BLE settings?, If yes, what is the way to do to accommodate the string length. 

[Simonr]

What tablets exactly are these, do they support BLE, and what version of BLE do they support, the nRF52840 might use features that aren't supported by your tablets? What SDK and SDK version have you built your nRF52840 project in? What exactly is the disconnect reason reported from the tablets and/or from the nRF52840?

Best regards,

Simon

[EVOV Solutions]

All these Tablets have BLE4.0 & above. I have already explained observation of BLE disconnection there is nothing more to add from our side.

[Simonr]

Hi

Sorry, but I'll have to disagree. Can you share some information on what exactly your nRF52840 application is doing. If it uses BLE 5.0 features such as long range or tries to do an MTU update with sizes that BLE 4.0/4.2 etc. does not support, that might be a disconnect reason. 

The best way to see what is going on over the air would be to take a sniffer trace of what is going on over the air. That way we can see what packets are sent over the air, and what transaction is causing this disconnect. If you have a dedicated Bluetooth sniffer device like an Ellisys sniffer you can use that, or you can use an nRF52 DK or Dongle and the nRF Sniffer + Wireshark.

If that's not possible from your end, can you upload the log showing the disconnect on the tablet (and preferably the nRF52 side as well), that's usually better than a description. Also, if you could share what SDK and SDK version you're using that would help as well. There are too many possible root causes from the current description.

Best regards,

Simon