Connect multiple identical BLE devices to Windows

[amit_ble]

I am using the STM32WB55 microcontroller for my product. I want to connect more than one module to my Windows laptop. When I pair one module, it pairs correctly, but when I try to connect another module with the same firmware, it shows the message "Try to connect your device again" and does not connect. I have tried changing many things, but it is still not working. Where do I need to make changes so I can connect both devices with the same firmware to my laptop?

[STTwo-32 · Accepted solution]

Hello @amit_ble 

This depends on the tolerated number of connections on the central side (your PC). And not on the STM32WB side (that will be the peripheral).So, please check the capability of your BLE module (on the PC).

Best Regards.

STTwo-32

[tmk]

Yes, there is a problem on the Window's driver. However, it can be resolved on the MCU side. For pairing, the devices use IRK and ERK to derive LTK and CSRK. For the peripheral devices which has the same firmware, it is likely that both devices are using same IRK and ERK to derive LTK and CSRK. As a result, it is possible that these identical devices are also generating identical LTK and CSRK which is a deal breaker for the Windows. 

Try making the IRK and ERK unique for each device (maybe change last 6 bytes of IRK and ERK to be the MAC address of BLE device - which is universally unique). This makes the IRK and ERK less random and less ideal to be used, but it is a workaround for Windows.