Why is a toroidal inductor being used in the RFID reader described in DIY FSK RFID Reader?

I feel that a toroidal inductor wouldn't be very effective in grasping the changes in electromagnetic field changes.

  • 1
    The word "toroidal" may be misapplied in the instructions. They don't show a picture, but their description doesn't seem to include any toroidal core which would contain internal / exclude external flux in the manner you are thinking of. Aug 3, 2014 at 14:04

1 Answer 1


Yes, Chris Stratton is right. A toroidal inductor keeps flux within the core, reduces the external flux to near zero and have near zero ability to grasp/convert external flux/magnetic field into electrical signal. Apparently, the word 'toroidal' was used in loose sense referring to a circularly shaped coil.

In an real-life commercial product, a 125 kHz coil typically has many turns on a very thin wire on an open-air core (no core).

An example profession factory made a 125 kHz RFID with a GitHub Arduino library and photos of an antenna coil:

Also, see Building RFID Card Reader using PIC Microcontroller.

Note, for higher frequency RFID, not shown in above examples, coils have fewer turns than for 125 kHz.

  • While this is supporting material, you have three answers here none of which answer the actual question which was asked. At the very least you should be combining them. Aug 4, 2014 at 1:15
  • So If they mean about circular Inductor for 'toroidal' ......why did they use 'former' word(empty scotch tape as former).... Aug 4, 2014 at 18:21
  • One link inside the article leads to this, forums.parallax.com/showthread.php/…. At middle page, the coil, same shape as the factory made example but bigger, is 'just visible' (red color wire) sitting under the white tag. Big size antenna, in this photo, can work longer, may be 6 to 12 inches, instead of the typical 1 to 2 inch when coil is human palm size
    – EEd
    Aug 4, 2014 at 19:10

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