ST25R Obtain RSSI of multiple tags

[he2]

Hello everyone,

I am working on a project that requires identifying the RSSI of all surrounding tags.
If "tag 6361" is not placed, the remaining three tags can be recognized and their RSSI can be obtained. However, after placing "tag 6361", only "tag 6361" can be recognized, and the other three tags cannot communicate.
The RSSI of the four tags is: tag "66E9" has an RSSI of 101, tag "635A" has an RSSI of 28, tag "681D" has an RSSI of 73, and tag "675A" has an RSSI of 1736.

May I ask how to make these four labels recognized simultaneously?

[Ulysses HERNIOSUS]

Hello He2,

I see typically two possibilities why such effects are appearing:

1. Your center tag causes heavy de-tuning and the tags further away don't get enough field strength anymore.
   This could be verified by placing a sniff coil - aligned to the tag - to see if it actually answers.
2. The center strong tag response is much stronger than the one of the others and the others are responding but are not recognized as collision/additional tags. This point goes then into protocol details which are handling simultaneous responses differently. Which type of tags are you using and which function from reader side?

Best Regards, Ulysses

[he2]

Hello Ulysses,

We use TYPE-5 tags, and the reader's function is to obtain the UUID of all surrounding tags and the RSSI of that tag.

Best Regards, He

[he2]

Hello Ulysses,

May I ask how to modify the chip to eliminate the impact of placing the "6361" label?

Best Regards, He

[Ulysses HERNIOSUS · Accepted solution]

Hello He,

I recommend to debug using method 1) to see if the outer tags are answering.

For NFCV tags you may want to use rfalNfcvPollerSleepCollisionResolution() which should avoid stronger tags covering weaker tags.

BR, Ulysses