PN7150 Reading Tag unreliable

[Janine]

Hello

I have problems reading tags reliably.

Hardware: Custom Board with PN7150
Tag: LXMS33HCNG-134
DH: Embedded Linux, using Library linux_nfc_api.h
Antenna and tag are at a fixed position towards one another.

Reading multiple blocks of the tags is done using the function nfcTag_transceive()
with the following ReadCmd: 

{0x02U, 0x23, /*block*/ 0x00, /* num Blocks 0x1C */ 28};

Analyzing the I2C communication between PN7150 and the DH I have the following different outcomes:

1. Tag recognizes immediately and read correctly
2. Tag recognized, the function is able to read multiple blocks after several read attempts.
   Unsuccessful attempts return "STATUS_RF_FRAME_CORRUPTED"
3. Tag recognized, but I2C communication stops mid Data Packets after the Notification Message is sent.
4. Tag nor recognized at all, returning CORE_GENERIC_ERROR_NTF, DISCOVERY_TARGET_ACTIVATION_FAILED

What could be the reason for this behavior? And how can I solve it?

[Tomas_Parizek]

Hello Janine, 

Please check this document -> https://www.nxp.com/docs/en/application-note/AN13892.pdf. (the principle is the same for PN7150 and PN7160)

Especially pages 20 and 21. I think the issue could be due to the high RX gain. 

BR

Tomas 

[Janine]

Hello Tomas

Thanks for your reply.

By default, the RX_GAIN (configured in libnfc-nxp-pn548.conf) was set to the maximum (57dB).

The first experiments look promising (for 40dB or 50dB, 33dB are not enough).
I will keep you posted.

Best regards,
Janine

[Tomas_Parizek]

Hello Janine,
Ok, please let us know if this helped.

BR
Tomas

[Janine]

Hi Daniel

Thanks a lot for your response. Sorry for not getting back sooner, I am still working on this and haven't found a reliable solution.

The distance between the reader and the tag is approx. 2.5mm.

The thing that still puzzles me is the following:
I had a setup in my lab, which was running flawlessly.
I then moved it into the field, same setup, no change of distance between tag and reader.
At the new location I have a lot of reading errors.

I cannot think of anything else besides temperature or humidity that is different.
Is the reader sensitive to those factors?

Thanks a lot for your help.

Regards,

Janine

[danielchen]

Hi Janine:

What is the distance between the reader and Tag?  maybe that is the maximum reader range for your project.  It is a critical distance.  Sometimes it can work, but not stable.   This is normal. 

 If you lower the distance, it should be stable.

Regards

Danie