NFC not working with Record Text Sample on the nRF52840 DK

[Aloysious Benoy]

Hi,

I was trying to get the NFC Sample programs to work on the nRF52840 DK but the NFC tag is not being read by my phone. The program itself is running (confimed through serial monitor output and by adding LED blinking etc). I tried both record_text and record_launch_app samples wihtout any success(I have attached the record_launch_app hex file for your testing). I tried using a OnePlus 12R as well as an iPhone 12 and the tag is not being detected by either phones. 
This issues happens only on the DK. I built the same code for the Seeed Studio XIAO BLE and it works with both phones with a small handmade NFC Antenna. Can you help debug why this issue is happening? I have ruled out antenna orientation by using a multimeter to check the connectivity between antenna and DK.

0045.merged.hex

[Turbo J]

Did you try to "recover" the board (west flash --recover)? Remember that the NFC pin config is in UICR and may be modifed in your DK. Flashing normally won't restore UICR values.

[Vidar Berg]

That is a good point. An ERASEALL trough west flash --recover or west flash --erase will ensure the UICR section is erased as well. However, the hex included by OP did not work for me either and I confirmed that UICR.NFCPINS was correctly configured for NFC operation. 

[Aloysious Benoy]

Thanks for that, the UICR config did not cross my mind! I had even tried on an nRF7002-DK (nRF5340) with no success. Maybe both boards come with the NFC pins set to GPIO mode by default?

Doing erase all/ erase uicr did the job, and even the original hex worked. Much thanks!

[Aloysious Benoy]

The original hex worked for me after erasing UICR. Now it is confusing as to why it is not working for you Vidar Berg 

[Vidar Berg]

Not sure what happened, but it’s possible I loaded the wrong merged.hex earlier. The hex file you uploaded does work now when I tried it again.