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  1. #1
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    rfid reader from multiple coils switching

    Hi

    I have having a problem designing an rfid receiver that can read from 4 antenais that can be controlled from the micro at any given time. Let me explain, I need to have 4 coils that can be switched to 1 rfid reader or circuit. I have found some circuit from microhip but nothing on switching between coils.

    Please help
    Thanks.

    •   Alt9th June 2010, 05:09

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  2. #2
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    Re: rfid reader from multiple coils switching

    Hi

    OK maybe a little explaination of what I am trying to do.

    I have 4 coils going small to large and all in a center on top of each other.
    Now I take a PUK and out a rfid in in, I slide the puk on top a table to circles.
    Now I can scan each cicrle to see where the puk landed.
    Hope this helps..

    So bascailly need to do 1 reader to scan 4 coils, it is for a game to tally the scores automatically. I may have 5th coil for outehr of table to detect out of zone.

    Please any help wouyld be great, will be costly if have to do 4 or 5 readers.

    Thank you :D



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    Re: rfid reader from multiple coils switching

    Unless you don't have the option to redesign the coil interface for multiplexed operation, use small relays, e.g with reed contacts.

    You told about different coil sizes. Are you aware of the necessity to tune the reader circuit to the coil? How do you want to achieve this?



    •   Alt10th June 2010, 06:32

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    Re: rfid reader from multiple coils switching

    We used 4051 analog multiplexors to design 40 inputs RFID and all they work well. Single U2270B chip is connected through 5 analog multiplexors 4051 to 40 different coils. We used ferrite inductors 5x10 750uH which could be obtained in any electronic shop. The detect distance was around 30mm.

    I'm talking about working solution, so 4051 is the way to extend the number of channels.



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    Re: rfid reader from multiple coils switching

    Hi

    Thank you for your input, I am looking at the microchip design circuit so will I use the 4051 on both sides of the coil? Or should it be used somewhere else in the circuit?

    Thank you



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    Re: rfid reader from multiple coils switching

    so will I use the 4051 on both sides of the coil
    You didn't tell about the RFID type (125 kHz, 13.56 MHz, ...) or reader chip. Some circuits probably work with a low voltage multiplexer like 4051, others won't.



  7. #7
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    Re: rfid reader from multiple coils switching

    See attached the schematic. the mux are connected only to one end of the U2270. so fo 40 RFID readers you need 5 chips 4051. All they work on 5V

    you need to adjust the values to have 125 KHz oscillations.



    •   Alt10th June 2010, 13:32

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  8. #8
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    Re: rfid reader from multiple coils switching

    BTW, the voltage on the coil could reach 15-20V if the componets were properly adjusted. You should not be fooled from the fact that 4051 uses 5V Vcc, the voltage on the coil is definetely higher than 5V.

    Similar schematic with 40 readers can scan 40 different RFID tags within 2s if the reading process was optmized.



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