Custom Board - nRF Toolkit HRS app Disconnects within 10 - 30 seconds

[Pradeep]

Hi,

I am facing an unusual issue. My team has created a custom board using nRF52 and testing with HRS sample from ble_peripheral folder. Using the nRF Connect mobile app, custom board is detected as Nordic_HRM during bluetooth scan. nRF Connect app is able to pair and connect to the custom board, from enable services option app is continuously reading the Heart Rate Measurement data.

From nrf Toolkit mobile app using HRM option the paired custom board is visible from connect option. App connects to the HRM and starts plotting the data in the graph.

nRF connect is continuously logging the BLE data and HRM in nRF toolkit stops plotting the data after about 10 to 30 seconds. The error in nRF connect log shows error as "Error 8 (0x8): Gatt Conn Timeout" and logging also stops also app disconnects from the Custom Board. Again I press on Connect button and nRF connect app successfully connects to the custom board and stars logging the HRM data. When I don't connect the HRM tool from nRF Toolkit, the nRF connect app continuously logs the data without any problems. Only on connecting HRM from nRF Toolkit, app disconnects in few seconds with error as "Error 8 (0x8): Gatt Conn Timeout".

With Only nRF Connect app connected to the custom board with HRM profile, the app is able to log continuously without any break in connection for about 6 hours.

I would like to understand why "Error 8 (0x8): Gatt Conn Timeout" is happening when HRM from nRF toolkit is connected.

I need assistance in identifying if this "Error 8 (0x8): Gatt Conn Timeout" is a software bug or hardware bug. After disconnect, the app is able to successfully connect back to the custom board, this indicates that the BLE stack is still operating without any problems. But, need a conformation from your end.

Appreciate an early response.

Thanks.

Regards, Pradeep

[Michael Antwih]

Are you able to attach a debugger to your custom board? If so I would suggest running the code via debug mode. You are most likely getting an app / system error. Examining the stack would help determine the last statement, calling function, etc.

[Pradeep]

Any other suggestions. I am really stuck on this.

I flashed the Proximity sample to my custom board, Time out error is happening every 20 - 30 seconds in nRF connect App. I am clueless where the issue is.

Need help !

[Michael Antwih]

Were you able to debug on the custom board side? Do the results change with difference distances between the two? Could it be an RSSI issue and you start dropping packages. the nrf Connect app is via a mobile device correct? Have you attempted to try a different mobile device to see if you get the same results.

If you have a nrf5x development board load your code on the development board and run it against the same nrf connect on the same mobile device you are having troubles with. This will tell you where it is hardware related or software related.

If it fails on the dvk then it is software related. If it works then most likely it is a RSSI issue so the antenna on the custom board might need tuning.

[Pradeep]

HRS and Proximity sample work perfectly in nRF52 Dev Kit, does not work as expected in my custom board. As per your suggestion, i believe it is most likely RSSI issues with antenna.

Could you provide some pointers on how to tune the antenna to resolve the RSSI issue?

[Michael Antwih]

Sorry for the delay. What type of antenna are you using in your design. Could you possible share that information with me. maybe in a pm if needed. Considering your antenna design and pcb stackup have you calculated the expected impedance of the rf path to get a general idea? If you don't have a network or spectrum analyzer the best bet would be to do the rough calculation to see where you sit if you believe it is RSSI related.

Another thing you can do to verify this is decrease the separation between the devices, meaning place the custom board pretty much on top of the device running the connect app. This will effectively provide an increase in RSSI and hopefully provide some information. I would actually try this first before doing any calculations since it is a very easy and quick thing to do.