Custom Board with BC40C (nRF5340) - Bluetooth won’t advertise after flashing Peripheral UART sample

RE: Custom Board with BC40C (nRF5340) - Bluetooth won’t advertise after flashing Peripheral UART sample

SwRa — Mon, 04 Aug 2025 11:52:24 GMT

Hi Lars,

The voltage differences you observe between your V1 (working) and V2 (non-working) are significant and likely indicate a hardware-level issue related to the board’s power supply or voltage reference. It is likely that you might have missed out some components. Do check the differences between the two boards.

Regards,

Swathy

RE: Custom Board with BC40C (nRF5340) - Bluetooth won’t advertise after flashing Peripheral UART sample

YeQuit — Sat, 26 Jul 2025 10:30:37 GMT

Hi SwRa,

Apologies for the late reply.

Unfortunately, Bluetooth is still not working. Here's what I’ve tried so far: The BC40C is an nRF5340 module with a built-in antenna, which requires no external components. BLE is definitely working on the BC40C modules in general.

I measured signals on both the working V1 PCB and the non-working V2 PCB.
The results are a bit surprising when compared side-by-side (see table below):

Pin	V1 (working PCB)	V2 (BLE not working)
SWDIO	3V3	3V3
SWCLK	0V / GND	1.8V
RESET	3V3	1.8V

Both PCBs were flashed with the same firmware.

As I mentioned before, we didn't make significant changes to the design between V1 and V2.

Is there any known behavior or issue that could explain these differences or might cause this kind of error?

Thanks again for your support!

RE: Custom Board with BC40C (nRF5340) - Bluetooth won’t advertise after flashing Peripheral UART sample

SwRa — Mon, 21 Jul 2025 13:11:14 GMT

Hi Lars,

The most likely possibility is that the network core is not programmed with the correct image (typically hci_rpmsg). In that case, bluetooth will not work, even if the application core is running fine. Bluetooth functionality is handled by the network core. You can refer this ticket: devzone.nordicsemi.com/.../327376

If your custom board does not have a 32.768 kHz crystal, you must configure the firmware to use the internal RC oscillator for the low-frequency clock on both the application and network cores. If this is not set, Bluetooth will not function. Also, if your board does not have DCDC inductors, you should disable DCDC in your configuration: CONFIG_BOARD_ENABLE_DCDC=n

These should help resolve the issue.

Best Regards,

Swathy