nRF9160 SIBA unable to connect to NB-IoT network and resets every ~10 seconds.

[elephant]

nRF9160 SIBA on custom board is unable to connect to NB-IOT and resets after about 10 seconds of operation.

Without a call to lte_lc_init_and_connect the reset does not happen.

The power, as suggested in other topics is at 2.6V from dc power supply with limit set to 1A.

Side note: this setting is the only one allowing for the programmer to reach the SiP. At planned 3.3V the programmer is not able to connect to the chip. For now just a missing power IC -> power supply is used.

[JONATHAN LL]

Hi,

Can you provide a log ?

What application are you using? 

Does this happen with the AT_client ?

What MF do you have?

Regards,
Jonathan

[elephant]

I am curious about two things by now. Is pin 57 really important for RF part of chip to work well? (it is MIPI VIO, not connected in my design)

And is antenna really mechanically symmetric, but electrically not? (As stated by Fractus antennas)

[JONATHAN LL]

pin 57 (VIO) is not curtail for RF operation. It is OK to have it floating. 


Error message  -116 (ETIMEDOUT) and  -120 (EALREADY) 

It is some sort of Time Out and it might be because it cant find a network, bad connection or a error with the SIM card or the SIM service/Subscription.

As for the comment on the antenna symmetry I am not 100% sure what you mean. Do you have a report from Fractus antennas on your board\layout or are you referring to the specs of the antenna? 

Regards,
Jonathan

[elephant]

Yes, to me it also looks like the devices is unable to find network. But the cellular tower is just about 20m away and I am working right next to the window. So the signal strength must be great and enough.

As for the symmetry of the antenna. Seen a note on that once in the documentation for fr01-S4-210, used in Thingy:91. Think this is no issue for nn03-310 used in my design, because no such notes in datasheet.

[JONATHAN LL]

From the documentation for the NN03-310 there seem to be no change other then a new name and updated datasheet.




Can you pleas you the AT client and give me the log from the following commands:

AT+CFUN=?

AT+CESQ=?

AT+CSQ=?

AT%XMONITOR

AT+CEREG=?

Regards
Jonathan

[elephant]

cfun: (0,1,2,4,20,21,30,31,40,41,44)

cfun = 1

cereg: (0,1,2)

cereg = 5, 2, 4b6c, 030d40de, 9

cesq: (99),(99),(255),(255),(0-34,255),(0-97,255)

cesq = ""

csq; (99),(99)

csq = ""

xmonitor = 2 (it was 4 earlier)

lte_lc_connect returns -8

[elephant]

Nah, xmonitor is 4 now again. Two steps before it was because of more experiments on my side. I added a short pin (4-6mm long) in place of antenna.

cfun is 1 and cereg is still at 5,2,... without pin.

[JONATHAN LL]

If XMONITOR = 2 or 4 then it is not connected


So it might be something with the sim card, what sim card and provider are you using ?


Edit:  I think there is a problem with the antenna, i would try to contact Fractus antenna and ask for a review and simulation of the board. 
With the CESQ it seems that there is 255 – Not known or not detectable. 

Alternatively you can create a new case, make it private, call it antenna layout review nrf9160 and add the HW files and schematic. And we will do our best to guide you.


Regards,
Jonathan

[elephant]

This very sim card is working in Thingy:91, so no problem with it itself.

Is there a way to know nRF9160 accepted it ok or with errors?

AT+CPIN? returns "OK"

AT+CIMI returns some valid-looking digits

any other tests I could do?

[JONATHAN LL]

I thin the issue is with the antenna, if the SIM works on a different device in the same location then the RF layout and antenna is probably the issue. 

I think there is a problem with the antenna, i would try to contact Fractus antenna and ask for a review and simulation of the board. 
With the CESQ it seems that there is 255 – Not known or not detectable. 

You can create a new case, make it private, call it antenna layout review nrf9160 and add the HW files and schematic. And we will do our best to guide you.

Regards,
Joanthan

[elephant]

Good news: it actually gets to about cesq = 99,99,255,255,24,40 and xmonitor = 2 after ~20 seconds of delay since at+cfun=1 command. But still no connection. Going to give it still more time.

Edit: after about 5-10 minutes no connection.

[elephant]

Just to conclude this. There appears to be some sort of a circuit break inside nRF9160. Most probably due to mounting procedures.

This is because antenna and matching network togather, connected to thingy:91 do really work. It connects ok just like with its own antenna. And thingy behaves just like my custom board when the wire is just touching a pad without proper soldering. This thing occurred spontaneously during experiments with the two boards.