Programming blank nRF52 ic ble issue - crystal issue

RE: Programming blank nRF52 ic ble issue - crystal issue

Dajgoro Labinac — Tue, 31 Jan 2017 12:41:58 GMT

Yes, I took care to leave as much ground plane as I could, and stitch it where is possible.
I copied the capacitor values from the devboard schematic, which might be the issue when using another crystal. I kinda bodged the smaller smd crystal on my pcb so I don't want to experiment on it anymore. I will solder a fresh PCB and try putting different capacitor values.

RE: Programming blank nRF52 ic ble issue - crystal issue

FormerMember — Tue, 31 Jan 2017 11:28:19 GMT

Okay, I see.

Do you have a lot of ground on your PCB?
The load capacitors for the 32 MHz crystal you are using, did you calculate the their value with respect to the crystal specification, using the formula in the tutorial I linked to? Wrong value on those capacitors will lead to wrong frequency of the crystal, which again will lead to wrong carrier frequency in the radio.

RE: Programming blank nRF52 ic ble issue - crystal issue

Dajgoro Labinac — Tue, 31 Jan 2017 10:45:43 GMT

I got it as tight as possible on a 2L board. Its not the issue with my board since the same issue happens on the devboard when I replace the 32MHz crystal there. So both boards behave identically with the crystals.

RE: Programming blank nRF52 ic ble issue - crystal issue

FormerMember — Tue, 31 Jan 2017 10:06:18 GMT

What about the layout?

RE: Programming blank nRF52 ic ble issue - crystal issue

Dajgoro Labinac — Tue, 31 Jan 2017 10:03:58 GMT

I just copied the schematic of the devboard and added voltage level converters and a max232 for serial. Thanks for that link.

RE: Programming blank nRF52 ic ble issue - crystal issue

FormerMember — Tue, 31 Jan 2017 08:21:53 GMT

@D101h: Could you upload the schematic and layout of the RF part of your PCB? Also, for some design guidelines with nRF52, it can be useful to take a look at this tutorial.

RE: Programming blank nRF52 ic ble issue - crystal issue

Dajgoro Labinac — Mon, 30 Jan 2017 16:03:44 GMT

There are two crystals, the 32.768kHz crystal oscillates constantly once the softdevice is programmed, and the other 32MHz crystal works in bursts. I even had issues with the 32kHz crystal that on the PCB i made i used a jelly bean watch crystal which did not work, but when I soldered a smaller(smd) one it worked. But this other is really strange, since when using the 32MHz crystal seems to work, but it does not. The issue is so sensitive that I can't figure it out by just watching the oscilloscope waveform, I'll have to make a more complex analysis. I have to know how to properly design the crystal section because I am developing a product which will use the nRF52 and I don't want devices mysteriously failing because of some oddity. Maybe I could ask on the eevblog forum.

RE: Programming blank nRF52 ic ble issue - crystal issue

Wojtek — Mon, 30 Jan 2017 14:19:51 GMT

Ah right. You mean 32khz oscillator? it is required to have at least +-250ppm frequency tolerance. I don't know about capacitors, but they have to be matched correctly somehow too (it is described somewhere here on the forum i think). So, it was clearly the hardware problem. Glad you solved it :)

RE: Programming blank nRF52 ic ble issue - crystal issue

Dajgoro Labinac — Mon, 30 Jan 2017 13:51:29 GMT

Found the problem! Thanks Wojtek for the support! Since you confirmed that all the steps were right, I went back to the HW. Once when I was fiddling with the devboard I accidentally blasted off the 32MHz crystal with hot air, so I placed some other crystal and checked it works with oscilloscope. And that seems to be the problem. The crystals (hc49 and smd ones) don't work. I have a DS2072A oscillsocope and I compared the waveforms of the original crystal from the new board and the waveform of the replaced crystal and they look identical. I can't figure out what makes the difference (yet), but must be something related to the crystal impendace. I bodged the smaller crystal from the devboard to my PCB and it works! What parameters are different with the crystal from the devboard compared to some other random crystal?

RE: Programming blank nRF52 ic ble issue - crystal issue

Wojtek — Mon, 30 Jan 2017 11:35:36 GMT

What I do with all my custom boards is just (in nrfgo studio or something else): full erase -> flash softdevice -> flash application. And so it works smoothly, of course. If you also do that steps and app does not work, something is wrong with your hardware. Maybe soldering, maybe something else. Are you able to debug?

RE: Programming blank nRF52 ic ble issue - crystal issue

Dajgoro Labinac — Mon, 30 Jan 2017 11:15:31 GMT

I tried fiddling with the hw a lot, and with the crystal too. I probed it with an oscilloscope and both crystals work fine. That is when I decided to replace the mcu on the devboard with a fresh one, and now I can't get that devboard working either.

RE: Programming blank nRF52 ic ble issue - crystal issue

Wojtek — Mon, 30 Jan 2017 10:57:31 GMT

If the same program works on DK and does not work on Your board, I would rather look on hardware for a problem, not the software... Just one blind shot - do you have 32khz crystal as LFCLK source?