nRF5340 bluetooth low energy signal never detected

RE: nRF5340 bluetooth low energy signal never detected

Priyanka — Mon, 31 Mar 2025 13:24:15 GMT

Glad that you were able to get it working for now. This is the guide (as mentioned earlier in this thread) that we have on the crystal caps:

https://devzone.nordicsemi.com/guides/hardware-design-test-and-measuring/b/nrf5x/posts/general-pcb-design-guidelines-for-nrf53-series#:~:text=The%20crystal%20oscillators

RE: nRF5340 bluetooth low energy signal never detected

Diogo_Simao — Wed, 26 Mar 2025 14:47:37 GMT

Finally found the culprit. We were using external capacitors for the 32 MHz oscillator, but weren't getting the right configurations... CONFIG_SOC_HFXO_CAP_EXTERNAL=y wasn't enough, and we tried a multitude of other configurations/combinations.

We removed the capacitors and used the DK .dts to allow it to use external capacitors and the beacon was detected by the nRF BLE app!

It's still a mystery as to what we were missing to use external capacitors, but we'll be redesigning hardware without them as we don't have a specific reason to use them as specifically external.

Would be good to know what exactly is the right setup for external capacitors anyway.

RE: nRF5340 bluetooth low energy signal never detected

Diogo_Simao — Mon, 24 Mar 2025 12:20:50 GMT

Apologies for the late response, we assembled another custom board to troubleshoot this further.

The problem remains the same, firmware/application runs well, I get no signal.

I've done a couple more things, disabled the DCDC mode in VREGRADIO and VREGMAIN to see if DC/DC or LDO made a difference (didn't detect anything either way). Although I did note that VREGMAIN isn't retained, I assume it's because I'm forcing things in the application side of things and there might be some configuration setting this to a default value on boot.

Read the MAINREGSTATUS to confirm its running in normal voltage mode (it is).

I've used either a WiFi antenna directly into the uFL or a ceramic antenna.

We haven't fully adapted the trace yet so the values of the passive components are subject to change, however I do believe I should be able to pick up any signal (small as it may be) with my phone on top of the antenna. Impedance matching should help a lot in a final application but when the antennas are 1 mm apart I should pick up something above -100dBm? Could it really be that off?

Here's the antenna bit of the schematic:

Could it possibly be some other register/configuration? The main differences from the dev kit is using USB-C data for debugging and using VDD 3V (I can't recall exactly how the nrf5340 dk regulated everything - VDDH setup with 3.0V external regulator?). Nothing else other than bluetooth and usb-c is being used at the moment.

P.S.: We'll be measuring the pins related to RF signal supply (DCC, DECR DECRF) to see if something is off, although I'm not sure what kind of values we should be expecting while the radio is trying to transmit.

Appreciate the help!

RE: nRF5340 bluetooth low energy signal never detected

Priyanka — Wed, 12 Mar 2025 14:16:20 GMT

Hi,

It definitely looks like a hardware issue so far. Have you connected the antenna via an adapter or directly?

Also, have you followed the antenna and impedance matching exactly as on the reference design including the components and their values?

Faulty soldering can also cause issues, as you have mentioned, so I would recommend that you go through this.

It's also a good idea to go through the nRF53 PCB guidelines as mentioned in the previous comment by @Anthony A Marchini

-Priyanka

RE: nRF5340 bluetooth low energy signal never detected

AMarch01 — Wed, 12 Mar 2025 13:03:23 GMT

A quick response would be if you have followed the guidelines for layout...however they don't have specifics on UFL antennas so maybe that doesn't help.

General PCB design guidelines for nRF53 series - nRF5x - Hardware design, test and measuring - Nordic DevZone