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Thread: Adding an external coil

  1. Adding an external coil

    I had, by occasion, the need to run an external coil from the reader. Though it's not in the Phidget RFID reader boards specification, testing has determined that it's possible to run an external coil directly from the boards inline coil.

    The coil used in the experiment, is 125khz 1.6 millihenry 4x4 inch square - approximately 30 gauge, 0.3150 mm dia laquered copper wire.

    The wires attached to it, are standard household speaker wire.




    On the front panel of the board, the first wire attaches to a hole where the inline coil terminates.





    A closer inspection.



    On the reverse of the board, the second wire attaches where the coil begins.



    A closer inspection, though, not much definition in the picture the 'black' circuit board proved incredibly difficult to photograph - you'll know the hole I'm talking about when you see it.



    I tested this set up using a 20ft speaker cable, and it's unlikely there's a range cap but I'll be sure to post if I discover one.

    The obvious applications for this arrangement, include operating the coil beyond the reader. So if you wanted to have a coil placed outside at your gate, then your Phidget board can stay indoors.

    It's also possible to arrange coils and switch between them, manually or otherwise.

    The coils are reasonably cheap, so depending on the application it may be advantageous to use several switched coils as opposed to several Phidget boards. In that respect, it would be possible to switch between a number of coils at intervals using a relay board to obtain sequential readings, and pair those readings via software with unique coil identifiers - this would be one alternative to switching between two or more boards.
    Last edited by Dave; 06-14-2007 at 08:42 AM. Reason: Moved pictures to ImageShack

  2. #2
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    Re: Adding an external coil

    That's pretty wicked! Thanks for the post and detailed images

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

  3. Re: Adding an external coil

    Hi,

    I just bought myself a PhidgetRFID reader and I want to add external coil to it (assuming this would make area for reading tags larger, correct?). Anyway, mine is version 206 (the one with a large hole). The PCB is slightly different, thus making the end where the coil starts placed somewhere else. The hole of where the coil ends is the same tho.

    So, my question is, how do I determine which hole is where the coil starts?

    Thank you.

    p/s: I'm no electronic guy and I have a very shallow idea about electronics.

  4. #4
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    Re: Adding an external coil

    I'm not sure how to do this, but if you're not an electronics guy, then I highly recommend against trying this mod, except of course if you have the funds and don't mind if you accidentally fry a $60 board.

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

  5. Re: Adding an external coil

    Quote Originally Posted by Cyphereza View Post
    Hi,

    I just bought myself a PhidgetRFID reader and I want to add external coil to it (assuming this would make area for reading tags larger, correct?). Anyway, mine is version 206 (the one with a large hole). The PCB is slightly different, thus making the end where the coil starts placed somewhere else. The hole of where the coil ends is the same tho.

    So, my question is, how do I determine which hole is where the coil starts?

    Thank you.

    p/s: I'm no electronic guy and I have a very shallow idea about electronics.
    I don't think you can squeeze more juice out of the Phidgets because it's inline coil is already optimally calibrated. So adding a larger coil won't do much because the amount of power doesn't increase by making the coil larger - if anything, you'll end up with a reflection area around the coil and possibly nothing in the middle, so what you gain in area, you'll quite possibly lose in range.

    The extension method is handy for using smaller coils and taking the reader out of whatever device your wanting to stuff a coil inside.

    If your thinking about using one of those DIY roll-you-own coils that look to be the size of a football, even when they're wired to a properly calibrated circuit they have a maximum range of about an inch.

    But, there may be alternative options, what is it that your hoping to accomplish?

  6. Re: Adding an external coil

    I'm hoping to get an area 6" x 4" covered with the antenna so that I'll have a bigger area to read the tags. Range isn't that important (1" or 2" reading would be fine by me).

  7. Re: Adding an external coil

    i'm sorry for the stupid question but with this hack both antennas will work? i would like to do this to use my reader on very thick door having the phidgets on the inside and the external antenna outside..

    thanks for the info

    mhc

  8. Re: Adding an external coil

    Quote Originally Posted by mhc21 View Post
    i'm sorry for the stupid question but with this hack both antennas will work? i would like to do this to use my reader on very thick door having the phidgets on the inside and the external antenna outside..

    thanks for the info

    mhc
    If you don't cut through the circuit, then yes the inline and external both work.

    "Cyphereza" it's possible, but depends on the tag and angle of reflection, and coil - I'd try but don't be disappointed if it doesn't work - all is not lost. If it doesn't work, you might want to consider stepping up to 13.56 as some can read over 8" out-of-the-box, and you won't need to build a custom coil.

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