How many peripherals can be connected to the central in the NUS multiple peripheral to central firmware.

[laumung]

Hello, I am making a system with 20 peripherals to a central base on nRF52840. I followed the firmware."ble_app_uart__saadc_timer_driven__scan_mode" from NORDIC playground in GITHUB for peripheral board and nrf52-ble-app-uart-c-multilink for central board. The peripherals advertise 224 bytes data every 20ms and the central receives data then transfer to laptop via UART. 

Now I can transfer 6 or 7 peripherals to the central, but when the peripherals increased to 18, many peripherals will stop advertising. There will be only two or three peripherals working at last. I remember nordic SDK should support 20 peripherals in this mode. Which parameter should I change to correct the errors? I can post my code for analysis. Any help will be appreciated. 

[Kenneth]

Hi,

With this amount of devices you will need to consider the connection intervals, for instance you should try to set the (min) connection interval when establish connection to 100ms for all connected devices, also check out:
https://infocenter.nordicsemi.com/topic/sds_s140/SDS/s1xx/multilink_scheduling/central_connection_timing.html 

Kenneth

[laumung]

Hi Kenneth, thank you for your reply. I read through the information in your post. I can understand the "scheduling"  for BLE advising and scanning. I have tried the parameters in the central board and sensor boards, but it didn't work well. I don't know which configuration is corresponding the parameters with the nordic manual for "multilink_scheduling". I changed the parameters as following but the multilink works not stable.

// <o> NRF_BLE_SCAN_SCAN_INTERVAL - Scanning interval. Determines the scan interval in units of 0.625 millisecond. 
#ifndef NRF_BLE_SCAN_SCAN_INTERVAL
#define NRF_BLE_SCAN_SCAN_INTERVAL 400      //160
#endif

// <o> NRF_BLE_SCAN_SCAN_DURATION - Duration of a scanning session in units of 10 ms. Range: 0x0001 - 0xFFFF (10 ms to 10.9225 ms). If set to 0x0000, the scanning continues until it is explicitly disabled. 
#ifndef NRF_BLE_SCAN_SCAN_DURATION
#define NRF_BLE_SCAN_SCAN_DURATION 0
#endif

// <o> NRF_BLE_SCAN_SCAN_WINDOW - Scanning window. Determines the scanning window in units of 0.625 millisecond. 
#ifndef NRF_BLE_SCAN_SCAN_WINDOW
#define NRF_BLE_SCAN_SCAN_WINDOW 200      // 80
#endif

// <o> NRF_BLE_SCAN_MIN_CONNECTION_INTERVAL - Determines minimum connection interval in milliseconds. 
#ifndef NRF_BLE_SCAN_MIN_CONNECTION_INTERVAL
#define NRF_BLE_SCAN_MIN_CONNECTION_INTERVAL 7.5       //7.5
#endif

// <o> NRF_BLE_SCAN_MAX_CONNECTION_INTERVAL - Determines maximum connection interval in milliseconds. 
#ifndef NRF_BLE_SCAN_MAX_CONNECTION_INTERVAL
#define NRF_BLE_SCAN_MAX_CONNECTION_INTERVAL 180      //30
#endif

How should I change the parameters for my project? What I need is to build 20 peripherals to 1 central BLE network using the NUS service. The advising interval of each peripheral is about 280ms and 224 bytes of data to transmit. What parameters should I modify to meet our project? Thanks.