Unable to Connect on Android After Connecting Via Bluetooth Device List

[WestCoastDaz]

We have been having a persistent issue with customers that have Android phones.  Our product uses the nRF SDK and we have a iPhone and Android Web app that is based on Cordova and Ionic.

We connect to our product within the our app without issue.  The problem is sometimes customers go to their Bluetooth Device list on their Android phone and try and connect to our product that way as it appears in the list of devices.  Once this happens then our app can no longer connect to the device on that phone without reseting the networking settings of that phone.  This doesn't happen with iPhones as our product never shows up in the Bluetooth Devices List.

Is it normal for the BLE devices to show in the Bluetooth Devices List on Android devices?  Is there a way to stop it showing up in that list or something else I can do so that it won't allow customers to try and connect that way?

Thanks,

[Aleksander Nowakowski]

Hello WestCoastDaz ,

When a user tries to connect to a device from Android Bluetooth settings, the phone will start bonding with the device, just as if you'd call "createBond" method. Do you support bonding in your firmware?

The Android Settings app can connect and bond to any device, but if it does not support it, it will disconnect afterwards. For example, HID devices are supported natively, so Android will keep and use the connection, but HRM device is not, so after bonding and service discovery Android would simply disconnect. During bonding, some other app may get an event that a device has connected, and it may also connect to it using "connectGatt" method. In that case, the physical connection will not be terminated, as at least one client on the phone is using it.

As far as I understand, in your app you may be doing something like:

1. not using bonding, but the device does not reject pairing request - if bonding implementation is not correct, this may cause troubles accessing some services.

2. storing the device address for the future - if the device got connected and bonded from another app (settings), your app was not involved in scanning and establishing connection, so you'd have to fix something on your side to support that case as well (e.g. receiving bonded devices or connected devices from bluetooth manager).

3. the device may still be connected to the phone while you're trying to scan for it, so it does not appear on scan results - you need to show connected/bonded devices in your app (unfortunately, you can't filter only those that have required services, like you could on iOS).

Do you support bonding on the device? How does your device behave when bonded? What is the difference when connected from your app and from the Android Settings?

Could you also say what do you mean by "reseting the networking settings of that phone."?

Best Regards,

Aleksander

[WestCoastDaz]

Hi Aleksander Nowakowski ,

Thank you for the detailed post.  No, we don't support bonding in our device.  To your point 1, no our app also doesn't use bonding nor does our device doesn't reject pairing requests.  

This project uses nRF52 SDK 16.0.0.  Is there some nRF SDK examples of rejecting pairing?  

Best Regards,

Darren

[WestCoastDaz]

Joakim Jakobsen 

Just checking in to see if you had a chance to look into this further?

Thanks,

Darren

[Joakim Jakobsen]

Hi Darren! 

Sorry this was left unanswered. I'll pick it up again and get back to you with. 

Thank you for you patience. 

Br, 
Joakim

[Joakim Jakobsen]

Hi again.

Could you try not initializing the peer manager and see if that removes the pairing pop-up?

Br,
Joakim

[WestCoastDaz]

Joakim Jakobsen 

I can try that and get back to you.  It will take me a couple of days as I'm working on something else at the moment.

Thanks,

[Joakim Jakobsen]

Of course!

Just update the ticket when you are ready and we'll do our best to assist you further.

Br,
Joakim

[Andrew]

We had exactly the same issue with some of our own users.  Once the Android OS had tried pairing it would then never be able to make a good connection to that device again - even if you unpaired it.  I seem to recall there was some method of clearing network settings off the phone, but it wasn't was and there was nothing we could do in firmware to recover once it had gone wrong.

We worked around this by rejecting a pairing request should the phone ever try and pair.  This stopped us getting into the errant state in the first place.  

This was achieved by adding the following case to ble_evt_handler() so that the BLE device tells the phone that it does not accept pairing.

        case BLE_GAP_EVT_SEC_PARAMS_REQUEST:
            // Pairing not supported
            NRF_LOG_INFO("reject the pairing request"); 
            sd_ble_gap_sec_params_reply(m_conn_handle,
                                                   BLE_GAP_SEC_STATUS_PAIRING_NOT_SUPP,
                                                   NULL,
                                                   NULL);
            break;