EEVblog #539 – RFID Tag Card Repair

Dave does an impromptu teardown and repairs his 125KHz RFID lab access card.
And finds a use for his DSO Quad oscilloscope.

Forum HERE

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    • Worf

      Actually, I believe the reader is looking for slight changes to the impedance caused by the card shorting the coil.

      Basically the reader emits a monitored 125kHz signal, and when a card is brought near, the change in the impedance of the sending coil is noted for a card presence. Then when the IC is powered up and transmitting, it shorts the coil, which cauess a marked change in the sending coil’s impedance (the two coils work like a transformer, so shorting the secondary end causes the primary to see a short as well as the transformer is also an impedance transforming device).

      It’s backscatter because the impedance change can be detected by other cards (and is used as a collision detection mechanism – if multiple cards are brought to it, the collision is detected when the card doesn’t short the coil, but detects that the coil impedance has been altered, which means the card should wait until the next read cycle. After successfully transmitting, the card shuts down to allow other cards to be identified).

      • EEVblog

        Cool, thanks for the info.

    • AJBotha

      lol @ the DaveCAD I think its funny!

    • Jan

      Please Dave, say some words in your next blog regarding the fires around Sydney. Are you or your house affected by these fires laid by some stupid youngsters, as mentioned in our news in Germany?

      • EEVblog

        The fires are only in the blue mountains (and other places) outside of Sydney.
        The army started the Blue Mountains fire!

    • f4eru

      a look on those kind of chips :

    • vasi

      Hi Dave,

      No need to burn the fire, just put an aspirin on the table, put the wire on the aspirin, get some solder on the tip of you iron, then press the tip on the wire. The aspirin underneath start to melt (avoid the nasty smoke/smell) and the enamel is replaced with a nice and shiny solder. Now you can join the two wires.

      The same tip a gave to the folks from TheBackShed forums. Tell me how it works.