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How physically close will a tag need to be for the phone to detect a NFC card? (10cm or can it greater)

Also can the phone present itself as a NFC tag to other phones? If this is possible is the range greater as the NFC transmitter is powered?

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up vote 4 down vote accepted

How physically close will a tag need to be for the phone to detect a NFC card? (10cm or can it greater)

NFC is intentionally very low ranged since it is meant to be difficult to accidentally connect to the wrong NFC readers. One of its possible applications is to aid in initiating longer-ranged connection (e.g. Bluetooth or Wifi) with zero configuration.

Also can the phone present itself as a NFC tag to other phones? If this is possible is the range greater as the NFC transmitter is powered?

There are plans for future Android releases to support NFC card emulation, but Nexus S won't be getting it since it lacks the necessary hardware. I can think of several ways to hack around this, with some limitations, since static NFC tag can be made as a sticker, but full NFC card emulation will not be available in Nexus S.

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Excuse me to dig up this topic, but I was under the assumption the NFC controller in the Nexus S is capable of all NFC communication - including card emulation - but its not (yet) supported on the software level..? Please don't tell me I should shatter that dream. –  JornC Mar 29 '11 at 14:23
    
@JornC: The link Lie posted seems pretty definitive to me. No NFC card emulation for the Nexus S. –  me_and Mar 29 '11 at 15:20
    
The Nexus S does have the hardware for card emulation, it has a PN544 chip, the specification for which is here: nxp.com/documents/leaflet/75016890.pdf which states "Card emulation ISO 14443 –A-B-B’, MIFARE, FeliCa RF" –  Peanut Apr 19 '12 at 10:49
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The Nexus S (and the Galaxy Nexus) actually contains a combination of the PN544 and a Secure Element (based on the SmartMX, a smart card IC). This allows the Nexus S to do card emulation as ISO 14443-A and MIFARE Classic. This is exactly what Google Wallet uses. –  NFC guy May 4 '12 at 7:47
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The specs on the NFC Controller chip in the Nexus S are the following: http://www.nxp.com/acrobat_download2/literature/9397/75016890.pdf

To answer your first question, as advertised in the above PDF, the NFC Controller chip inside the Nexus S has an operating distance of about 10 centimeters. However, in practice (specific to the NFC controller in the Nexus S that is), it's limited to about 4 centimeters. You practically have to hold the card to the back of the phone in order for it to be able to read the card. 10 centimeters is massively over-exaggerated, 4 centimeters is the farthest I could go with any card. Distance is greatly dependant on the quality of the RF transmitter, and receiver on the other end, so this distance may very well increase under different conditions. If you have specialized equipment, it's possible to pick up any NFC RF communication up to a distance of about 10 meters, but don't expect NFC implementations in phones to go any farther then 10 centimeters.

For your second question. Again, as advertised in the above PDF, card emulation (the ability to present oneself as a NFC tag) is supported for the following standards: ISO 14443 –A-B-B’, MIFARE, FeliCa RF. To my knowledge, these are all the standards one should (currently) care about.

However, card emulation is not supported by the Android SDK, and I'm not sure whether or not it will be supported in future versions, or even if Android Devs are working on such functionality. It would, however, be the logical next step for the Android SDK to support.

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The link Lie posted seems pretty definitive to me. No NFC card emulation for the Nexus S. –  me_and Mar 29 '11 at 15:20
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Thanks for cleaning this up. –  Matthew Read Mar 30 '11 at 15:03
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I know this already has an accepted answer and is quite old but the answer is wrong.

"How physically close will a tag need to be for the phone to detect a NFC card? (10cm or can it greater)"

The answer quotes < 0.2m but that's from the NFC standard, the actual distance depends on the radius of the NFC chip's antennae, in the case of the Nexus S is can detect a tag from about 4cm or less, as the other non-accepted answer says.

"Also can the phone present itself as a NFC tag to other phones? If this is possible is the range greater as the NFC transmitter is powered?"

Yes it can, kind of. It can 'push' an NDEF message containing information (plain text/URL/others) and if you put another Nexus S next to it then you can read it with NXPs NFC application, or other ones. I'm not aware of any applications currently on the market than can push an arbitrary NDEF message but if you have ICS then this has the Android 'Beam' feature which utilises NDEF messages. http://www.engadget.com/2011/12/01/android-4-0-ice-cream-sandwich-review/#beam

It can also do card emulation as is used in Google Wallet but this isn't supported in the public API. However have a look at this for a Gingerbread ROM with emulation features: http://forum.xda-developers.com/showthread.php?t=1281946

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