ST25R3911B-DISCO for RFID mid-range in a box with constraints

[MelioNB]

Hello,

I am a French engineering student working on a startup project as part of my MBA. We are developing an interactive musical box for children aged 3 to 7 years old.

The core feature of the product relies on RFID detection: small figurines shaped like musical instruments are placed on a circular rotating tray (15 cm diameter). Each figurine has an RFID tag under its base. When a figurine is placed on the tray, the reader must detect it and trigger the corresponding audio track.

Here are our technical constraints:
- The reader will be fixed under the tray, at a very short vertical distance (1 to 2 cm at most)
- The detection zone must cover the full surface of the tray, meaning a lateral radius of 7.5 cm
- The tags will be in slow rotational movement
- The reader must be connectable to a PC via USB for prototyping purposes, so we can retrieve detected tag UIDs in real time via a Python or JavaScript script
- Budget constraint: under 100€

After research, we identified the ST25R3911B-DISCO evaluation kit as a potential candidate, notably for its ISO 15693 long-range support and its USB connectivity.

Our question is: would the ST25R3911B-DISCO, paired with an appropriately sized antenna, be able to reliably detect ISO 15693 tags across a 15 cm diameter surface at a very short vertical distance? And if so, what antenna size and configuration would you recommend for this use case?

Thank you very much for your time and support.

[Travis Palmer]

 Hello MelioNB,

in terms of cost efficiency I would recommend to look into the X-NUCLEO-NFC05A1 board and a NUCLEO-L476RG. 

The advantage is that the NUCLEO-L476RG embeds already the programmer an more IOs then the DISCO board. But it is required to do your own software.

The ST25R3911B can perfectly do the job, but there are newer products (including more features) like the ST25R210 (X-NUCLEO-NFC13A1) which might be also interesting for you. 

I would recommend to disconnect the antenna of the X-NUCLEO-NFC__A1 and replace it by an wire-wound antenna. Such an approach has already been done in this post: 

https://community.st.com/t5/st25-nfc-rfid-tags-and-readers/design-questions-around-st25r3911b/m-p/370090

From antenna matching perspective the same approach (strong capacitive matching) as mentioned in AN6092 can be applied on both devices (R3911B and R210). Otherwise the antenna matching guide for ST25R3911B is AN4974.

Key aspect will be the tag antenna size. At a 15cm diameter antenna, there will be a weak spot in the center of the antenna. If a conventional NFC antenna (2-3 Turns at the 15cm diameter perimeter) is not sufficient also other tricks can be used. A wire-wound antenna offers the advantage of easily changing the geometry, rematching the board, and evaluating the result again.

Please let me know if you have additional questions.

BR Travis

[Grégoire Poulain]

Hello MelioNB,

Complementing Travis answer, another option under ST25R portfolio is the ST25R200 and ST25R100.
These devices are very cost-effective and seem to suit well your use case (ISO15693 Reader mode).

As for the demo boards, all ST25R boards interface with PC via USB.

• The older devices use a proprietary communication on top of USB HID Class.
• The newer demos (since ST25R200) use USB connection, but over a virtual COM port (ST-Link).
  Through it, a defined ST protocol is exchanged which could be used for your use case.

Kits available:

• STEVAL-25R200SA Kit allows easy prototyping with different antenna options/geometries.
  A PC GUI (STSW-ST25R019) which connects to the board over USB (ST-Link) can be used for prototyping
  
  
• X-NUCLEO-NFC09A1 / X-NUCLEO-NFC10A1 NUCLEO Shield also available.
  No PC GUI available by default on NUCLEO demo (targeted for embedded) but is possible to run the the STEVAL FW directly on the NUCLEO STM32G0 board to connect with the GUI (in this case on NUCLEO-G0B1RE).

Concerning integration into development environments, C and Pythion examples are provided.
After installing STEVAL GUI, look into MyDocuments\STMicroelectronics\ST25Rxxx_Eval_GUI

Hope it helps
GP

[MelioNB]

Hello Travis and Grégoire,

Really appreciate you both taking the time to answer.

After looking into the options you mentioned, I'm going with the STEVAL-25R200SA because it ticks all the boxes for us: right budget, ISO 15693, USB connection to PC, and the different antenna options will be great for testing.

Thanks again, I'll come back if I encounter any problems