Writing to 20 NFC Stickers: Can X-NUCLEO-NFC12A1 Do Antenna Multiplexing

[pnuno_2002]

Hi,

I need to write the same kind of NDEF data to ~20 different NFC stickers placed on a panel. The idea is to have ~20 small antennas, select one at a time, and write to the sticker sitting above that antenna.

Questions:

• Can I do this with X-NUCLEO-NFC12A1 + STM32 by multiplexing the RF path (switches/decoder → select 1-of-20 antennas)?

• Any recommended switch/multiplexer parts or reference designs for 13.56 MHz?

• What are the practical limits on antenna count and cable/trace length when switching like this?

• Do I need individual tuning (matching caps) per antenna position?

• Is there a better Nucleo shield for this use-case (e.g., higher RF drive) or is NFC12A1 enough?

Goal: operator chooses pad 1…20, we write an NDEF, verify, then move to the next pad.

Kindly advise—example schematics/app notes or code pointers would be great.

Rgds,
Rp

#stm32 #nfc #x-nucleo-nfc12a1 #antenna #multiplexing #ndef

[Travis Palmer · Accepted solution]

Hi pnuno_2002,

please have a look at AN6121.

There are also some interesting posts regarding this topic.

Please have a look at this post.

• Can I do this with X-NUCLEO-NFC12A1 + STM32 by multiplexing the RF path (switches/decoder → select 1-of-20 antennas)?

  • Yes, please take a look at AN6121 as a reference. 

• Any recommended switch/multiplexer parts or reference designs for 13.56 MHz?

  • There are very little multiplexer ICs available for NFC/RF  applications. (either too low voltage or too high dcr). This is why we came up with AN6121.

• What are the practical limits on antenna count and cable/trace length when switching like this?

  • At the end with every antenna and every cm of trace, additional parasitic capacitance is being added. It is hard to predict a maximum number of antennas. 

• Do I need individual tuning (matching caps) per antenna position?

  • Yes, due to the parasitic capacitances and different environmental effects it might be required to tune each antenna individually.

• Is there a better Nucleo shield for this use-case (e.g., higher RF drive) or is NFC12A1 enough?

  • At the end you will need to design one PCB implementing the NFC IC and multiplexer. The antennas can either be dedicated or part of this PCB. A dedicated antenna (twisted pair cable or coaxial cable) makes it hard to predict parasitic components. Please have a look at AN5592.

Please let us know, if you have additional quesitons.

br Travis

[pnuno_2002]

Hi Travis,

Thank you very much for your detailed reply and for the references.
They were really helpful.

I have one additional question regarding the use of the X-NUCLEO-NFC12A1.
Is there any library, example or API that allows writing data to the stickers/tags directly from the nucleo board?
I’ve been checking the available examples but so far I haven’t found anything related to writing to NFC tags, so I would appreciate any guidance on where to look.

Thanks again for your support.

Best regards,
pnuno_2002

[Ulysses HERNIOSUS]

Hi,

the X-CUBE-NFC12 should contain an ndef example. Using the user button you can traverse through ndef read, ndef write and ndef format. The formatting only works for ST25 tags.

Or you use a mobile with an app from the manufacturer of the tag. This gives the biggest flexibility.

BR, Ulysses