Problem reading Ble characteristics on android

[JOK]

Hi all,

I'm working on a custom Ble service based on this tutorial: https://github.com/bjornspockeli/custom_ble_service_example on nrf52840.

I've been able to add about 50 characteristics. I've tested reading/writing on windows and android with nrf connect. On windows I'm able to read and write all characteristics, but on android it seems that I can only read/write the first 32 chars. All other chars are listed as descriptor.(see image) 

Is there some kind of a limit? Why is it working on windows but not on android?

Thanks

 

[bjorn-spockeli]

Hi JOK, 

Yes, there seems to be a limit on the number of characteristics that an Android device can discover during service discovery, see https://stackoverflow.com/questions/24531334/is-there-any-limit-on-characteristics-uuid-in-android-ble and https://issuetracker.google.com/issues/37005408. 

Best regards

Bjørn

[JOK]

Hi Bjørn,

Thanks for your answer, but I don't fully understand the issue. There is a limit of 40 chars defined in Android. Is this a limit of 40 chars in a service or 40 chars in total in all services. 

In the first case I should split the service into multiple smaller services. If the second case is true, I probably have a problem ;-) Any ideas on this?

BTW: it seems that this issue is solved in newer Android versions:

https://devzone.nordicsemi.com/f/nordic-q-a/48172/characteristics-count-limit-on-android

[bjorn-spockeli]

I do not think that splitting one service with 50 characteristics into two services with 25 characteristics each will solve the issue. I suspect that you will see issues with the second service, e.g. that the last 10 or so characteristics of the second service will be listed as descriptors of the 15th characteristic.

However I have not tested this, so I might be wrong.  As mentioned  by another user in the question you referred to,  do you need 50 characteristics? 

JOK said:

BTW: it seems that this issue is solved in newer Android versions:

https://devzone.nordicsemi.com/f/nordic-q-a/48172/characteristics-count-limit-on-android

 Yes, but you need to remember that most smartphone vendors adapt the Android OS so adding changes might take a long time.