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TRF7961: questions on distance

Juan Gonzales
Mastermind 37340 points
Part Number: TRF7961
Other Parts Discussed in Thread: RF37S114

  1. I want to let sensing distance during the range,such as (5mm,15mm),which parameter or circuit shall I adjust to meet the rang?
  2. How long sensing distance does TRF7961 support didn’t see it in datasheet;
  3. If I fail to read or write the data into tag,is there any solution to fix it, such as reset controller, etc,the software solution is better?

  • 0
    TI__Guru* 91206 points

    Juan - 

    reading distance is mainly determined by power out of the reader, size of reader and tag antennas, the coupling factor between the two and the Q of both sides.

    to give an estimate of the read area, would need to know the intended size of the reader antenna and the size of the intended transponder to be used (and the PN of the transponder to be used, if possible)

    for deducing range, a system can be characterized and then the RSSI values can be used to infer range, in that scenario.

    if writing fails in the tag, you do get notifications from the tag, based on the protocol being used and then standard practice would be to retry 

     

  • 0 in reply to Josh Wyatt
    TI__Mastermind 37340 points

    Josh,

    I suspected the answer was not that straightforward.  Perhaps a better question would be if the high end of distance we are trying to measure (15mm) is easily doable in your experience, if it is challenging but possible, or if it is unheard of and not likely.  This would give us a good feel for the design effort.

    Thank you in advance!

  • 0 in reply to Juan Gonzales
    TI__Guru* 91206 points
    15mm is no problem usually for HF RFID. if the tag is very small and/or the reader antenna was very small, it might be a challenge - would need to know the dimensions they have in mind to make an educated guess.
  • 0 in reply to Josh Wyatt
    TI__Guru* 91206 points

    for example, a couple videos
    www.youtube.com/watch (this is example of the kind of control of the magnetic field that can be achieved)

    here is one that shows small tags and displaying RSSI
    www.youtube.com/watch

  • 0
    TI__Guru*** 135355 points

    Hello Juan,

    1. That range will be easy to meet unless the tags used are very small. Are there plans to use the 4x4mm ISO15693 TI has? RF37S114 is GPN for that. If they are using anything decently sized they should have no issue with that range. The key will be to ensure good tuning and Q factor.

    2. This is, as Josh indicated, application specific and entirely dependent on the tag size and reader antenna size. It also depends if 3V or 5V is used with the device.

    3. There are a few cases for this:

    • One is what Josh mentioned, where you get feedback from the tag that a failure occurred - in this case, a retry is recommended
    • Another is that no reply is received at all from the tag - in this case, a retry can be tried, or the communication sequence can be reset and start with Inventory to ID tag(s) again
    • An error such a CRC error or an unexpected collision error occurs - in this case, the device should be soft reset by using the 0x83 0x80 command sequence for SOFT INIT and IDLE direct commands, and then all registers should be re-configured and communication should be restarted from the beginning of the sequence (I.E. send an Inventory command) - this will ensure the device is in a good state after receiving an error
    • In the event they are in a situation where multiple tags are expected to be used and they are anticipating collisions, then collisions errors should be handled by:
      • Using anticollision sequence for ISO15693 to identify all tags in the RF field before sending out read/write commands
      • Send out read/write commands with addressed flag, so only a targeted tag can reply
      • If a collision error is received when sending an addressed command, it should be treated as an error and the device should be reset as outlined above.
      • It is not possible to read multiple tags with a single command, but it is possible - though highly discouraged - to write multiple tags with a single command. Writing without address is dangerous as it will indiscriminately write all tags and can cause VERY poor user experience if tags that weren't meant to be written get overridden!!