ST25R3911: reading distance of 20cm. Reading time in 1ms

[VSELL.1]

Hi, I'd like to use a ST25R3911 in order to detect a tag at approximately 20cm.

Do you think it's possible ?

--> I'll use custom antenna, and probably a custom protocol in order to read a small quantity of data ( my objectif is to read the data in 1ms)

[Travis Palmer · Accepted solution]

Hello Vsell,

20cm should not be an issue. It of course depends on reader and tag antenna size. The perimeter / size should be sufficient big. There are some threads about antenna tuning and how to achieve higher read range, which also contains pictures of the self made antenna.

I would recommend you to look into the ST25R3916(B). It has a better receiver than the ST25R3911B, which can be very beneficial for such long range reading tasks.

The reading duration is something different. A normal passive tag requires a contentious field on before the first command is transmitted, in order to power up. This time is called guard time and defined in various standards. It is also different for different technologies. e.g. ISO14443-A ~5.1ms.

Doing a proprietary protocol achieving a time below or within 1ms may require a powered device on the other side. (e.g. Dynamic Tag or Reader with card emulation functionality e.g. ST25R3916(B)).

If it is feasible to use a Dynamic Tag for such a task, a colleague with more knowledge about the Dynamic tags may answer.

br Travis

[VSELL.1]

Thank you for you answer, I'll look more into the ST25R3916(B) for the long-range subject.

Unfortunately, I have a constraint in my project that does not allow me to use Active tag or any source of power.

I'm going to keep looking for a solution (RFID or not)

[VSELL.1]

Hi Travis, I keep working on my RFID project and I manage to increase my reading time to approximately 20ms. I don't know yet if I’ll use a dynamic tag such as ST25DV04 or design a custom tag in order to customize the protocol and increase the time needed to send data (probably only 32 bits, something like that)

I have 2 more questions regarding this :

• When i use the ST25R2911B discovery GUI, I saw that the time needed for "Identification" is really fast compared to the time needed to read a single block can you explain me why ?
• And second question about my matching. I match my reader antenna like this :

but the results are not really good. Is there a problem somewhere? I use a 2 turn 20x30cm antenna, is my inductor value too high?

Tank you

Vincent

[Travis Palmer]

Hello Vincent,

I assume you are using the inventory command to collect all UIIDs in the field. The disco GUI is driving the ST25R3911B. So there is the USB interface in between. this is causing additional delays. It might be possible to further optimize if the code is directly running on the MCU. If you could share a bit more details about the used commands we could do further proposals.

The inductance value should be still in a good range. Can you maybe share the smith chart coming from the VNA?

Thanks, BR Travis