BLE Multi-Link connection - Maximum devices

[believer]

Hi,

I am currently using NRF52832 with SDK17.0.0.

As I know, a BLE central device can reach up to 20 peripheral devices.

So if I use an Android App as a central device, can I have more than just 20 connections?

Thank you.

[Mishka]

Hi,

I doubt so, because an Android device will limit the number of concurrent connection to only 7 as defined with BTA_GATTC_CONN_MAX (please see Android Bluetooth stack).

Also, the SoftDevice limits total number of concurrent connections to 20 (i.e. as central + peripheral). However, it should be possible to maintain more than 20 non-simultaneous links, i.e. maintain number of connection handles below the limit.

[believer]

Hi, I have seen this video. As you can see, an Android device phone can control 20 devices at the same time.

I have some unclear ideas with your answer, can you explain about 7 & 20 connections as mentioned above? 

[Amanda Hsieh]

Hi, 

In that video, the phone only connected to the aggregator running on an nRF52840DK which will collect information on all the connected devices and relay the information to the UART and to the connected smartphone over BLE. From the phone application, the user can control the LED color and state of the connected devices. The video illustrates the multi-role and multi PHY capabilities of the Nordic SoftDevices running on nRF52840DK. By using the 20 link feature of the S132 or S140 SoftDevices the aggregator can connect to up to 20 devices at the same time, where 19 of these devices will be ble_app_blinky or Thingy devices, and 1 device can be a smartphone. As for Android BL concurrent connection maximum, please see this thread.

-Amanda H. 

[believer]

Thank you for the very detailed information.

In my application, I want my app can control about 20 devices simultaneously. Can I do that with BLE?

[Amanda Hsieh]

With Nordic softdevice s140/s132 as the example in the demo video, you only can control 19 devices simultaneously, but you can take a look at this post. 

The support staff is reduced during the summer holidays, and you may experience delayed answers.

-Amanda H.