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PN532 antenna placed close to the field of 125 kHz reader

Question asked by Vadym Mishchuk on Oct 26, 2017

Hello, engineers.

My current project is small device, which reads MIFARE and EM-Marine cards and  interacts with smartphones by the means of NFC. NXP PN532 is used for reading MIFARE cards, TI RF430CL330 dynamic tag is used for interaction with smartphones, and simple 125kHz reader circuit for reading Em-Marine cards. All the Antennas will be put together like on the following picture

Antenna placement

At the moment I have prototype with PN532 and RF430 installed: it can read MIFARE classic cards as well as interact with smartphones. Each 400 ms it performs following cycle:

1. enable PN532 RF

2. For 200 ms try to select tags in field. If there are any, read them.

3. disable PN532 RF

4. For 200 ms wait for RF430 captured by external smartphone field. If captured, wait for end of write.

5. Go to step 1.

So now everything works like a charm and no collision appear, which is good because when I tried to use MFRC522 instead PN532 too many errors appeared when reading dynamic tag with smartphones (can someone explain that BTW?).

Question 1: What will happen if I add 125 khz antenna? From PN532 user manual I see that this device has lots of settings (I use this library). If there are any caveats about this I can modify library to prevent collisions or damage of the PN532 chip.

Question 2: For development purposes I use this cheap modules. Entire module cost less than 5 bucks. How is that possible? I mean that is cheaper than PN532 chips from digikey in quantity. Are they counterfeit? However I've got a bunch of those modules and can you give me a hint on how to check whether they are original or not? Here is photo of one of them.

pn532 chinese module photo

Question 3: Dynamic tag was used instead PN532 emulation feature because there are a lot of smartphones, that does not support reading and writing MIFARE tags (which seems to be the only feature supported by the arduino PN532 library). Is it possible to emulate non-MIFARE tag (tag type 4, for example) with pn532 (I don't take felica into account)?

Will appreciate any help or advice.

Reagrds, Vadym Mishchuk.