NFC reader detection field?

[Jeff King]

Hello:

I've got a application where I want to detect if the NRF52 is near a NFC reader. I don't need two way communications, but it would be good if the reader could modulate the 13.56 mhz signal (and I can do this custom in hardware if need be).  Using just a oscilloscope and a raw NFC 13.56mhz antenna I can detect energy out to about 10 inches with just a stock reader or Android phone. 

Can the NFC hardware/software be set to detect a NFC field? 

[endnode]

Yes indeed Jeff, nRF52 NFC front-end can detect the field and you can get event FIELDDETECTED event callback. You can also wake up the device by 13.56MHz field from SYSTEM_OFF mode (see SDK "./examples/nfc/wake_on_nfc/").

[Jeff King]

Thank you, that gave me enough direction to dig into it further. But I had some followup questions.

Under the hardware spec, the field detect needed 1 volt peak to peak signal to trigger. I didn't see where it was settable in firmware. I'm able to get good decodes on the scope in the 10mv  (0.01 VPP) level.   I realize the assumption of 1 VPP is with the back-channel (loading) modulation which I don't need.

To expand on what I am trying to do, I want a NRF52 tag to recognize when it is near a NFC reader, which will be configured as a beacon... thing of active RFID vs. passive. So my "reader" will be custom, and won't be a reader, just sending out a modulated 13.56mhz signal that the NRF52 needs to decode via the NFC pins in/antenna.

So the specific followup questions would be:

Can I get the decoder to trigger/work below 1Vpp?  (if not I imagine I can add a amp ahead of things)

Can I decode one way data? 

I realize this is out of spec for the part, but using NFC would allow me to use the NFC module as a choke point decoder for finer accuracy in location applications. 

[endnode]

Interesting idea. Be careful if you want to commercialize it, it will be 95% patented;) Anyway I can not comment on signal strength and sensitivity of FIELDDETECT on nRF52. As far as I know from my experience with 13.56MHz technologies it will in the end highly rely on HW design, antenna tuning etc. So do your prototype and tests, you will see the detection somewhere, hard to say if it will be closer to 10mm or to 100mm...

[Jeff King]

It's already in the public domain, known as choke-points. The difference here is the NRF52 has the hardware already on board, or at least it appears to.

So where we are at it seems is it can detect a field, but we don't know if there is a way to set it less then 1 Vpp

Also we don't know how low a level the NRF52 will decode the 13.56mhz signal.

Is there anyone on here from Nordic, who is familiar with the hardware of the chip?

[Kaja]

Hi Jeff, 

I'm sorry but I can not advice you to go out of spec, the specifications are there for a reason. 
As endnode said, it's difficult to achieve range with NFC, and you have to design, test, tune the NFC antenna. 

Best regards.
Kaja