Reading range for MFRC522 mini

what is the maximum reading range of MFRC522 mini?
How can I increase the reading range of MFRC522 mini?
When I use it in my project the reading range is 2c.m.

What does the datasheet tell?

In MFRC522 datasheet it says 5c.m. But with MFRC522 (not mini) I got a reading range of 4c.m

This is typical for a cheap all in one reader.

Pay attention to how and where it is mounted. Have it at least 1 meter from any other RFID reader, this distance applies through walls and doors as well. So for an in and out reader on a door don't mount them on the same side just to make the wiring easy.

Also make sure they are away from metal as far as possible. Do not mount them on a metal, or metal lined door or wall. Try and use nylon nuts and bolts and things like plywood mounting.

The most important thing however is the coil, which is an antenna. Normally this comes down to two things:-

  1. The size of the coil. The bigger it is the more range you will get.
  2. The coil must be tuned to be resonant with the transmit and receive frequencies. These two are not always the same thing, many RFID readers transmit at 13.56 MHz and receive at a quarter of this. To tune a coil you need frequency measuring equipment and an assortment of ceramic capacitors. You add or remove capacitors to get to the approximate resonance frequency. Capacitors may be connected in parallel to adjust the real value by small amounts. The trap here is if you get the coil spot on the resonant frequency it will perform poorly, you need it about 3% off frequency. This is symmetrical up and down from the resonant frequency.

Most mass produced readers are not individually tuned, but given the often 20% tolerance of the capacitor value, they need to be.

P.S. I used to design RFID readers for a job I had in an access control company.

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