Device crashes when I use a Crystal substitute

RE: Device crashes when I use a Crystal substitute

Martin Sivertsen — Wed, 26 Jan 2022 15:40:08 GMT

Hi,

What we do is measure the radio signal using a coaxial probe connected a signal and spectrum analyzer and look at the carrier frequency while the nRF device is in TX mode. You can see the offset of the carrier frequency and measure the frequency offset in parts per million by dividing the offset (in kHz) by the carrier frequency (in GHz), for example an offset of 15 kHz on a 2.44 GHz signal gives an offset of 15/2.44 = 6.15 PPM.

If this is not an option for you, you can measure directly on the crystal, but would have to use active probes with a very low capacitance. The trouble is that the probes might add load capacitance and change the frequency of the crystal. 5 to 10 pF is enough to alter the frequency by a significant amount (up to tens of kHz).

Best regards,

Martin S.

RE: Device crashes when I use a Crystal substitute

Tarik — Wed, 26 Jan 2022 11:16:46 GMT

Hi Martin,

Thanks for the feedback. is there a way to reliably measure the high frequency 32 MHz crystal with an oscilloscope ?

Thanks

RE: Device crashes when I use a Crystal substitute

Martin Sivertsen — Tue, 25 Jan 2022 15:29:52 GMT

Hi Tarik,

It could indeed be the crystals, both the frequency tolerance (as you've touched upon) and that the crystals have the same load capacitance as the ones we recommend.

Here you can see the frequency tolerance limits and load capacitance we operate with for the nRF52832: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/clock.html?cp=4_2_0_18_3#unique_582893628

Have you checked that these parameters are within spec?

Best regards,

Martin S.

RE: Device crashes when I use a Crystal substitute

Tarik — Tue, 25 Jan 2022 06:53:08 GMT

I just made some rework on the PCB, and replaced both the crystals by Epson's Q22FA12800025 and FC-135 32.768KHZ ±20PPM,9.0PF and put the Substitute crystals on an old working PCB.

The Old working PCB is still working even with the new substitute crystal, while the new PCB is still not working even with the Epson recommended crystals.

This means the issue does not come from the crystals. What other hardware issue can cause ble_stack_init() to crash?

(I tested the PCB with peripheral test example firmwares, and it seems to be working properly it only crashes with bluetooth examples at ble_stack_init())

Thanks

RE: Device crashes when I use a Crystal substitute

Martin Sivertsen — Mon, 24 Jan 2022 08:46:35 GMT

Hello Tarik,

I'll take a look at this and get back to you tomorrow.

Best regards,

Martin S.