ST25R3916 NFC RFID - Phone Detection

[berkayCinci]

Hello,

Is it possible to detect a phone using NFC/RFID readers?

I am working on a wireless charger unit and trying to detect credit cards. When I put a mobile phone with a credit card, I am not able to detect credit card because phone is getting started to charge. I want to learn whether it is possible to detect phone using ST25 NFC Readers. 

Is it possible to read Q value of NFC side? After we talked with the vendor of power transmitter, he suggested us to read Q value of NFC side. 

[Ulysses HERNIOSUS]

Hello berkayCinci,

not sure if I am following you all the way. Maybe a few questions first:

1. The credit card you are talking: Is it a physical one, attached to the phone? Or is it one loaded into the phone and emulated by the phone?
2. I assume you have a Qi Wireless charger with an NFC reader antenna around?!
3. Your goal is to read the card, while the phone is being charged?

Typically Qi chargers are concerned about not damaging physical NFC cards with the Qi charging field (or analog or digital Qi ping).

Best Regards, Ulysses

[Andrew Neil]

Your post seems contradictory: you start by saying you want to detect the phone, but the rest of the question seems to be about detecting (and reading?) a credit card?

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@berkayCinci wrote:

When I put a mobile phone with a credit card, I am not able to detect credit card because phone is getting started to charge.. 

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So you have detected the phone!

Or is the question really whether you can use both wireless charging and NFC comms at the same time ?

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@berkayCinci wrote:

I want to learn whether it is possible to detect phone using ST25 NFC Readers. 

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Have you tried that without wireless charging?

[berkayCinci]

Hello Ulysses,

1. The credit card you are talking: Is it a physical one, attached to the phone? Or is it one loaded into the phone and emulated by the phone? It is a physical credit card attacted to the phone.
2. I assume you have a Qi Wireless charger with an NFC reader antenna around?! Yes, It is Qi wireless charger with a NFC reader antenna.
3. Your goal is to read the card, while the phone is being charged? We are able to detect the card standalone. When we put a credit card behind the phone, we are not able to detect credit card all the time. Our aim is to detect the card in all scenarios. We are planning to initiate Power Transmitter in STOP mode(Idle State) when we power the device up. Is it possible to detect the phone by NFC RFID Reader. If we could detect any Rx Device, we will start charging by switching Power Transmitter to RUN Mode. Also, we need to distinguish RFID Card and Phone by NFC RFID Reader. 

[Ulysses HERNIOSUS]

Hello berkayCinci,

there are actually multiple aspects to what you are describing:

1. There is detuning of the system happening when both the phone and the card are in specific positions where likely the card does not even get enough energy. This is something to be solved in HW: tuning, antenna geometry, possibly AAT
2. The phone (depending on its settings) will also answer to NFC requests. Inside RFAL we have the rfal_cd layer which tries to identify if a card or a phone or both are present from the data exchanges and announced tag properties/behavior. In case the rfal_cd is not enough for you then you may discuss with your local ST supports on an extended mode in our software.

BR, Ulysses

[berkayCinci]

Hello Ulysess,

Thank you for the answer. Is there any possibility to measure Q-Factor by NFC Reader? Could we use Q-factor for the indication of that phone is detected?  

Best regards,

Berkay

[Ulysses HERNIOSUS]

Hello Berkay,

Q cannot be measured by the NFC reader. What ST25R3916 can measure is Amplitude and Phase of the carrier at RFI pins. 

The wake-up system is using this to detect changes caused by an approaching NFC card or phone.

Regards, Ulysses

[yusufekici]

Hi Ulysses,

Let me clarify two conditions:

1. We want to detect if any phone is placed on the NFC reader, even if the phone does not have NFC functionality. Currently, there is no way to determine this from the NFC reader.

2. The new rfal_cd you will provide should help us with two points:

   1. A quicker RFID tag detection process.
   2. The ability to distinguish between a phone with an emulated NFC tag and a normal RFID tag.

Can you confirm these two points?

[Ulysses HERNIOSUS]

Hi Berkay,

for your first question: We cannot propose a good way to detect a non-NFC phone on the antenna with NFC. I presume very hard to discriminate from other objects (key-rings, etc.).

rfal_cd: I confirm your two points. 

For a charger I would see as typical approach to always perform card/phone detection via NFC using rfal_cd before doing analog/digital Qi ping. If no device or only a phone with NFC being detected it would then move to Qi analog/digital ping. This way it would then discover in Qi step also phones which don't have NFC (enabled).

BR, Ulysses

[yusufekici]

Hi Ulysses,

1. Detecting an object would work for us. Once an object is detected, we can check for an NFC tag. If no tag is found, we can proceed to the charging phase. If the object is not a phone, we can switch back to an idle phase.

2. Our charger currently cannot detect a phone, which is one of our problems. Additionally, if we turn on the charger, it automatically goes into the charging state if any phone is found. This is why we need a phone detection mechanism, as the charger may enter the charging state before our NFC task detects any RFID card.

Here’s the process we are following:

• We start in idle mode.
• In a separate task, we poll for any RFID detection via NFC.
• If no RFID is found, we turn on the charger. In this case, the charger alternates between Q-Measurement and Digital Ping states while polling for RFID detection continues in another task.
• If we detect any RFID via NFC, we turn off the charger.

There is no problem if a standalone RFID card is placed on the charger, as we can stop immediately. However, if someone places a phone with an RFID card stuck to its back on the charger, the charger might enter the charging state before we detect the RFID.