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RFID readers synchronization

Akash Nakarmi
Prodigy 190 points


I have two S251B readers with 20 cm x 20 cm small gate antennas connected to each of them. In my application, the antennas are only 15 in apart from their centers. They seem to interfere each other.

I read synchronization schemes explained in http://www.ti.com/litv/pdf/scba019. I tried wireless synchronization and it did not help and carrier-phase synchronization together. it didn't help either. The antennas needed to be kept at least 1.5 m apart for them not to interfere each other. Then I went on to try No Sync along with carrier-phase synchronization, which seemed to work, but the reader (master) continuously reads tag kept close to it, while the other reader (slave) reads for some time, then loses for a while and again reads for another while. This cycle continues for the slave reader.

Could anyone help me with this issue? Why is the slave unit showing such behavior? How can I solve this problem?

Thank you. Your help will be highly appreciated.

-Akash

  • 0
    Prodigy 190 points

    Now I have configured my readers to Idle read mode. So that I can read them on demand. I'm trying Master/Slave synchronization without acknowledgement. I have one antenna connected to Master unit and another to Slave unit. The antennas are around 20 in apart from their centers. When I put tags at the center of both the antennas, I can read both the tags without any problem. When I remove one of the tags, then I can see that both the antennas are reading the same tag.

    Then I went on to try Carrie-Phase synchronization in conjunction with Master/Slave scheme. This doesn't seem to help at all in resolving the issue. When I keep the antennas at least 1.5 m apart, I don't see any problem. I moved the RF Power Adjustment in anti-clockwise direction, as far as it could go on both the readers. It didn't seem to help either. I reduced tag charge time from 50 ms to 25 ms and it doesn't seem to help either.

    My antennas are laying on a wooden surface surface. I am using the same voltage supply to power both my readers.

    Could you please help me troubleshoot?

  • 0 in reply to Akash Nakarmi
    Intellectual 305 points

    The Master/Slave setup is probably the only good solution if your antenna's are close to eachother. Check your Master/Slave synchronisation with an oscilloscope to see if they really trigger at the same time. (each 50ms? in burst mode)

    I think you have problems with oversampling... you should not put the wires of your antenna's close together!  The wire is antenna itself and can easily pass it's signal to a nearby wire. I assume this is your problem