One Plus 5T Cannot connect to BLE

[you can123]

Hi nordic:

When I connected the Bluetooth, I encountered the occasional mobile phone unable to connect error. In most cases, it is normal, but occasionally the error of unable to connect occurs, especially the One Plus 5T mobile phone, which basically fails to connect.
My environment is as follows:
SDK: 17.0.2

MCU：52840
Parameter configuration:

#define APP_ADV_FAST_INTERVAL               MSEC_TO_UNITS(1000, UNIT_0_625_MS)//800 
#define APP_ADV_FAST_DURATION          		0                                       

#define APP_ADV_SLOW_INTERVAL				MSEC_TO_UNITS(2000, UNIT_0_625_MS)		
#define APP_ADV_SLOW_DURATION               0//18000                           		


#define BATTERY_LEVEL_MEAS_INTERVAL         2000                                    
#define MIN_BATTERY_LEVEL                   81                                      
#define MAX_BATTERY_LEVEL                   100                                     
#define BATTERY_LEVEL_INCREMENT             1                                       

#define HEART_RATE_MEAS_INTERVAL            1000                                    
#define MIN_HEART_RATE                      140                                     
#define MAX_HEART_RATE                      300                                     
#define HEART_RATE_INCREMENT                10                                      


#define MIN_CONN_INTERVAL                   MSEC_TO_UNITS(7.5, UNIT_1_25_MS)      
#define MAX_CONN_INTERVAL                   MSEC_TO_UNITS(30, UNIT_1_25_MS)       
#define SLAVE_LATENCY                       6                                     
#define CONN_SUP_TIMEOUT                    MSEC_TO_UNITS(4000, UNIT_10_MS)       

#define FIRST_CONN_PARAMS_UPDATE_DELAY      5000                                  
#define NEXT_CONN_PARAMS_UPDATE_DELAY       30000    

This is the log of the connection error:

     

[Simonr]

Hi, the 133 GATT error is an infamous one that's unfortunately still present in some Android phones. I would suggest that you either try adding a few retries or a delay when connecting to GATT in your application, to see if that fixes these connection issues.

Best regards,

Simon

[you can123]

Are there other ways to avoid this error?

[Simonr]

Well, you can also try implementing a delay between connection attempts to mitigate these disconnects as well.

Another thing that's not guaranteed to work, is to tweak the connection parameters a bit (mainly increase connection intervals) to see if that makes it occurrences rarer.

Best regards,

Simon

[you can123]

OK, let me try it, are there any suggested parameters?

[Simonr]

Hi

I think most Android devices aren't able to connect with connection intervals lower than 15ms, so setting the minimum to 15ms for example, and leave the maximum at 30 or try increasing it to 100ms should give good results. If you're still running into these errors, I think you have to include some retries to the connection process on the nRF side.

Best regards,

Simon